■.j'HiiwiinHnnnouummnwK 
 
 m»immm \ w ■ii i i»)i i !i i i | i!i|iiii > i;i i | i i « |W M» « «ww ^ ^ 
 
 ■iiiiiw|i;ilii!i>ki|iiiiiiii<wiu>iM»<|i>iiii;iniiMii.iniliiiiani}«m)'<l 
 
Class 
 
 S r>cij 
 
 Book... 
 
 Cop)^§htN^_ 
 
 CDPVRIGKT DEPOSm 
 
XTbe IRural Science Series 
 
 Edited by L. H. BAILEY 
 
 THE BREEDING OF ANIMALS 
 
W^t Eural Science Series 
 
 Edited by L. H. Bailey 
 
 The Soil. King. 
 
 The Spraying of Plants. Lodeman. 
 
 Milk AND ITS Products. Wing. Enlarged and Bevised. 
 
 The Fertility of the Land. Boberts. 
 
 The Principles of Fruit-growing. Bailey. 20th 
 
 Edition., Bevised. 
 Bush-fruits. Card. Bevised. 
 Fertilizers. Voorhees. Bevised. 
 The Principles of Agriculture. Bailey. Bevised. 
 Irrigation and Drainage. King. 
 The Farmstead. Boberts. 
 Rural Wealth and Welfare. Fairchild. 
 The Principles of Vegetable-gardening. Bailey. 
 Farm Poultry. Watson. Enlarged and Bevised. 
 The Feeding of Animals. Jordan. (Now Rural 
 
 Text-Book Series. ) 
 The Farmer's Business Handbook. Boberts. 
 The Diseases of Animals. Mayo. 
 The Horse. Boberts. 
 How TO Choose a Farm. Hunt. 
 Forage Crops. Voorhees. 
 
 Bacteria in Relation to Country Life. Lipman. 
 The Nursery-book. Bailey. 
 Plant-breeding. Bailey and Gilbert. Bevised. 
 The Forcing-book. Bailey. 
 
 The Pruning-book. Bailey. (Now Rural Manual Series.) 
 Fruit-growing in Arid Regions. Paddock and Whipple. 
 Rural Hygiene. Ogden. 
 Dry-farming. Widtsoe. 
 Law for the American Farmer. Green. 
 Farm Boys and Girls. McKeever. 
 The Training and Breaking of Horses. Harper. 
 Sheep-farming in North America. Craig. 
 Cooperation in Agriculture. Powell. 
 The Farm Woodlot. Cheyney and Wentling. 
 Household Insects. Herrick. 
 Citrus Fruits. Coit. 
 
 Principles of Rural Credits. Morman. 
 Beekeeping. Phillips. 
 
 Subtropical Vegetable-gardening. Bolfs. 
 The Potato. Gilbert. 
 
THE 
 
 BREEDmG OF ANIMALS 
 
 Ft BrMUMFORD, M.S. 
 
 DEAN OF THE COLLEGE OF AGRICULTURE AND 
 
 DIRECTOR OF THE EXPERIMENT STATION 
 
 OF THE UNIVERSITY OF MISSOURI 
 
 THE MACMILLAN COMPANY 
 1917 
 
 All rights I'eserved 
 
. II s 
 
 Copyright, 1917, 
 By the MACMILLAN COMPANY. 
 
 Set up and electrotyped. Published February, 1917. 
 
 MAR -I lyl7 
 
 J. S. Cashing Co. — Berwick & Smith Co. 
 Norwood, Mass., U.S.A. 
 
 S)C1..A457249 
 
PREFACE 
 
 The problems of the animal-breeder may all be 
 grouped under the three subjects, reproduction, inherit- 
 ance, development. The mere multiplication of the 
 species is now, and always has been, the major work of 
 the breeder of domestic animals. But the real breeder 
 is not only concerned with the production of mere 
 numbers of animals of a given species but is primarily 
 interested in securing animals possessing the largest 
 number of desirable qualities and the least number of 
 qualities undesirable to man. 
 
 How to maintain the good qualities that have already 
 appeared in an individual, and how to cause other and 
 better qualities to become dominant in future indi- 
 viduals of the same species, is the problem of inheritance 
 that chiefly concerns the breeder of the domestic ani- 
 mals. The highest attainments in the breeder's art 
 have come only to those who have had a good knowl- 
 edge of the principles and laws of heredity. The de- 
 velopment of animals from the fertilization of the egg 
 to maturity and their proper maintenance throughout 
 their productive lives is second in importance only to 
 inheritance. The environment of the animal, including 
 food, climate, and exercise of functions, determines the 
 degree of development in the individual animal. The 
 term Development, as used in this connection, has refer- 
 ence to the unfolding of capabilities that have come to 
 the animal through inheritance. 
 
vi PREFACE 
 
 The author has made no attempt to write a book on 
 genetics or evolution ; but the principles of genetics as 
 they apply to the practice of animal-breeding are dis- 
 cussed, in accordance with the conclusions of biologists. 
 The problems of the animal-breeder are in many im- 
 portant particulars widely different from those of the 
 plant-breeder ; and the emphasis has been placed on 
 those principles and practices that belong peculiarly to 
 the province of the animal-breeder, while not neglecting 
 the lessons and illustrations to be drawn from the other 
 field. 
 
 It has been the purpose to make a practical book 
 which shall be directly useful to the student and to the 
 breeder of animals, and the lessons and examples of 
 which can be applied in the laboratory and on the farm. 
 
 F. B. MUMFORD. 
 
 Columbia, Mo. 
 
 November, 1916. 
 
TABLE OF CONTENTS 
 
 CHAPTER I 
 
 PAGES 
 
 The Cell 1-15 
 
 The cell theory, 1 ; The germ-cells, 2 ; The cell, 3 ; Is 
 the cell the physiological unit ? 4 ; The structure of the 
 cell, 5 ; Protoplasm, 6 ; The nucleus, 7 ; Growth by cell 
 division, 8 ; How cells divide, 9 ; Prophase, 10 ; Meta- 
 phase, 11 ; Anaphase, 12 ; Telophase, 13; The germ-cells 
 in detail, 14 ; The ovum, 15 ; The spermatozoon, 16. 
 
 CHAPTER II 
 
 Reproduction ......... 16-51 
 
 Asexual reproduction, 17 ; Sexual reproduction, 18 ; 
 The reproductive process, 19 ; Oviparous animals, 20 ; 
 Primary and secondary sexual characters, 21 ; The re- 
 productive organs of the male, 22 ; The testicles, 23 ; 
 Castration, 24; The reproductive organs of the female, 
 25 ; The ovaries, 26 ; The Fallopian tubes, 27 ; The 
 uterus, 28 ; The mammary glands, 29 ; Structure of 
 mammary glands, 30 ; Pertilization of the ovum, 31 ; 
 The nature of fertilization, 32 ; The process of fertiliza- 
 tion, 33 ; The chromosomes, 34 ; Results of the union of 
 egg and sperm, 35 ; Changes in the ovum, 36 ; Changes 
 in the spermatozoon, 37 ; The significance of reduction, 
 38 ; The origin of the germ-cells, 39 ; Maturation and 
 reduction in the female (oogenesis), 40 ; Reduction in 
 the male (spermatogenesis), 41 ; The period of the 
 oestrum or heat, 42 ; Artificial insemination, 43 ; Meth- 
 ods of artificial insemination, 44 ; Conditions influenc- 
 ing the vitality of the sperm-cells, 45 ; Effect of too 
 
 vii 
 
viii TABLE OF CONTENTS 
 
 PAOE8 
 
 frequent breeding on the sperm-cells, 46 ; Vitality of 
 spermatozoa within the female generative organs, 47 ; 
 Effect of intoxication of the male parent on his off- 
 spring, 48 ; Effect of lead poisoning on the male germ- 
 cells as indicated by the offspring, 49. 
 
 CHAPTER III 
 
 The Breeding Season 52-66 
 
 Changed conditions, 50 ; Phases of the breeding sea- 
 son, 51 ; Prooestrum, 62 ; Oestrum, 53 ; Metoestrum, 54 ; 
 Dicestrum, 55 ; Puberty, 56 ; Conditions influencing 
 puberty, 57 ; The oestrum and lactation, 58 ; Heat dur- 
 ing pregnancy, 59 ; Superfoetation, 60 ; Examples of 
 superfoetation, 61 ; Recurrence and duration of the 
 oestrum, 62 ; Effect of ration on recurrence of oestrum, 63. 
 
 CHAPTER IV 
 Gestation and Lactation ....... 66-84 
 
 Gestation : Indications of pregnancy, 64 ; Physical 
 examination for pregnancy, 65 ; The period of gestation, 
 66 ; Causes of variation in length of gestation period, 67 ; 
 Incubation, 68 ; Parturition, 69 ; Normal parturition of 
 the domestic animals, 70 ; Mal-presentations, 71 ; Normal 
 presentations, 72 ; Treatment for mal-presentation, 73. 
 
 Lactation : The mammary glands, 74 ; The duration 
 of lactation, 75 ; The food supply, 76 ; Habit, 77 ; He- 
 redity, 78 ; Exercise, 79 ; Climate, 80 ; Unusual lacta- 
 tion, 81. 
 
 CHAPTER V 
 Fertility .......... 85-112 
 
 The number of young at a birth, 82 ; Period of gesta- 
 tion and fertility, 83 ; Fertility and the frequency of the 
 recurrence of the oestrum, 84 ; Fertility and gestation, 85 ; 
 Duration of the reproductive period, 86; Confinement 
 and fertility, 87 ; The fertility of domesticated animals, 
 88 ; Age and fertility, 89 ; Relation of age to fertility in 
 
TABLE OF CONTENTS IX 
 
 PAGES 
 
 swine, 90 ; Influence of age of sow on size of litter, 91 ; Re- 
 lation of age to fertility in sheep, 92 ; Influence of age 
 of ram on fertility of ewes, 93 ; The effect of the age of 
 poultry parents on the offspring, 94 ; Age and fecundity, 
 95 ; Nutrition and fertility, 96 ; Excessive food supply 
 and nutrition, 97 ; Other factors affecting fertility, 98 ; 
 Relation of number of mammae in swine to fertility, 99 ; 
 Twins, 100 ; Characters correlated with fertility, 101 ; In- 
 breeding and fertility, 102 ; Cross-breeding and fertility, 
 103 ; Unusual fertility, 104 ; Unusual fertility among 
 horses, 105 ; Unusual fertility among cattle, 106 ; Un- 
 usual fertility among sheep, 107 ; Unusual fertility 
 among swine, 108 ; Unusual fertility among poultry, 109. 
 
 CHAPTER VI 
 
 Sterility 113-130 
 
 The causes of sterility, 110 ; Causes of sterility in the 
 male. 111 ; Sterility in the female, 112 ; Closure of the 
 cervix, 113 ; Obstruction of Fallopian tubes resulting 
 from excessive fatness, 114 ; Other causes of barrenness, 
 115 ; Sterility from fatty degeneration, 116 ; Sterility 
 caused by abortion, 117 ; Contagious abortion and ste- 
 rility, 118 ; Treatment for contagious abortion, 119 ; 
 Diagnosis of contagious abortion, 120 ; The complement 
 fixation test, 121 ; Sterility of free-martins, 122. 
 
 CHAPTER VII 
 
 Heredity 131-156 
 
 Development, 123 ; Heredity defined, 124 ; Heredity 
 and variation not antagonistic, 125; The kinds of he- 
 redity, 126 ; Blending inheritance, 127 ; Alternative in- 
 heritance, 128 ; Particulate or mosaic inheritance, 129 ; 
 Mendelian inheritance, 130 ; The experiments of Men- 
 del, 131 ; The law of dominance, 132 ; The law of seg- 
 regation, 133; Unit characters, 134; Gametic purity, 
 135 ; Application of Mendel's law, 136 ; The complexity 
 of animal characters, 137 ; The inheritance of polled and 
 horned character in cattle, 138 ; Theory of pure lines, 
 
X TABLE OF CONTENTS 
 
 PAGES 
 
 139 ; Hallett's wheat breeding, 140 ; The presence and 
 absence hypothesis, 141 ; The theory of mutations, 142 ; 
 Two important classes of variation, 143 ; Kinds of muta- 
 tions, 144 ; Importance of the mutation theory, 145 ; 
 Mono-hybrids and di-hybrids, 146. 
 
 CHAPTER VIII 
 
 Inheritance of Acquired Characters .... 157-182 
 Belief in transmission of acquired characters, 147 ; 
 Practical breeders believe in transmission of acquired 
 characters, 148 ; Nature and nurture, 149 ; What are 
 acquired characters ? 150 ; Somatoplasm and germ- 
 plasm, 151 ; Examples of acquired characters, 152 ; Food 
 supply, 153 ; Influence of the amount of food on body 
 weight, 154 ; Food supply and body changes, 155 ; In- 
 fluence of limited food supply from birth, 156 ; Teleg- 
 ony, 157 ; The Lord Morton mare, 158 ; The Penycuik 
 experiments, 159 ; Telegony and mule hybrids, 160 ; 
 Example of horse foals, 161 ; Possibility of influence 
 from a previous impregnation, 162; Xenia in animals, 
 163 ; Xenia among poultry, 164. 
 
 Objections to the Theory that Acquired Characters are 
 Transmitted : No mechanism for the inheritance of ac- 
 quired characters, 165 ; The inheritance of disease, 166 ; 
 Acquired diseases, 167 ; Congenital disease, 168 ; Pre- 
 disposition to disease, 169; Immunity, 170. 
 
 CHAPTER IX 
 
 Heredity and Sex 183-194 
 
 The significance of conjugation and fertilization, 171 ; 
 Secondary sexual characters, 172 ; Secondary sexual 
 characters and vigor, 173 ; Effects of castration and 
 ovariotomy on the secondary sexual characters, 174 ; 
 Effect of transplanting sexual glands, 175 ; Effect of 
 internal secretion, 176 ; Sex-linked characters, 177 ; 
 Color-blindness, 178 ; Controlling the sex of offspring, 
 179 ; Age or vigor of parents, 180 ; Comparative vigor ov 
 
TABLE OF CONTENTS XI 
 
 PAGES 
 
 sexual superiority, 181 ; Nutrition and sex, 182 ; The 
 maturity of the ovum, 183 ; Seasonal variations in pro- 
 portion of sexes, 184 ; Sex cannot be controlled by ex- 
 ternal conditions, 185. 
 
 CHAPTER X 
 
 Variation 195-216 
 
 Importance of variability, 186 ; Morphological varia- 
 tions, 187 ; Physiological variations, 188 ; Meristic vari- 
 ation, 189 ; Functional variations, 190 ; Examples of 
 functional variation, 191 ; Variation in fertility of ani- 
 mals, 192 ; Variation in the milking function, 193 ; 
 Variations among different cows, 194 ; New characters 
 originate in the germ-plasm, 195 ; Mutilations, 196 ; The 
 Brown-Sequard experiments, 197 ; Causes of variation, 
 198 ; Cell division a cause of variation, 199 ; Influence 
 of use and disuse in causing modifications, 200 ; Im- 
 portance of causes of variation to the breeder of domes- 
 tic animals, 201 ; Germinal variations, 202. 
 
 CHAPTER XI 
 
 In-breeding 217-242 
 
 Definitions, 203 ; Advantages claimed for in-breeding, 
 204 ; Bad results from in-breeding, 205 ; Decreased fer- 
 tility and vigor from in-breeding, 206 ; Darwin's re- 
 searches, 207 ; In-breeding cattle, 208 ; The Chillingham 
 cattle, 209; Deer in parks, 210; In-breeding among pigs, • 
 211 ; In-breeding sheep, 212 ; In-breeding dogs, 213 ; 
 Cornevin's experiments, 214 ; Weismann's and Von 
 Guaita's experiments, 215 ; Researches of Ritzema Bos, 
 216 ; The Wistar Institute experiments, 217 ; In-breeding 
 Berkshires by Mr. Gentry, 218 ; In-breeding corn, 219 ; 
 How long is it safe to continue in-breeding ? 220 ; Selec- 
 tion important, 221 ; The truth about in-breeding, 222 ; 
 Fixing characters by in-breeding, 223 ; In-breeding and 
 prepotency, 224 ; Results of in-breeding vary with dif- 
 ferent species, 225. 
 
xii TABLE OF CONTENTS 
 
 CHAPTER XII 
 
 PAGES 
 
 Cross-breeding 243-254 
 
 Permanent and temporary results of cross-breeding, 
 226 ; Advantages from cross-breeding, 227 ; Grading, 
 228 ; Cross-breeding to increase fertility, 229 ; Cross- 
 breeding to increase size and restore constitution, 230 ; 
 Crossing and heredity, 231 ; First cross and improve- 
 ment, 232 ; Cross-breeding as a cause of variation, 233 ; 
 Crossing species, 234 ; Crossing bison and cattle, 235 ; 
 The mule hybrid, 236 ; The hinny hybrid, 237 ; Cross- 
 ing the horse and the zebra, 238 ; Crossing cattle and 
 zebu, 239 ; Sheep-goat hybrid, 240. 
 
 CHAPTER XIII 
 Development ......... 255-279 
 
 Growth, 241 ; The growth impulse, 242 ; Factors in- 
 fluencing growth, 243 ; Growth and food supply, 244 ; 
 Capacity to grow, 246 ; Growth and the cell, 246 ; When 
 the growth impulse is strongest, 247 ; Development of 
 the foetus, 248 ; Heredity and foetal development, 249 ; 
 Birth weight of lambs, 250 ; Effect of protein and ash in 
 ration on foetal development, 251 ; High calcium rations 
 for pregnant swine, 252 ; Size and vigor of foetus as in- 
 fluenced by corn and wheat rations, 253 ; The perma- 
 nent effect of retarded growth, 254 ; Early stunting and 
 the capacity to grow, 255 ; Climate, 256 ; The age factor 
 in animal-breeding, 257 ; Premature breeding decreases 
 size, 258 ; Decreased size due to early breeding not in- 
 herited, 259 ; Influence of early pregnancy on the 
 mother, 260 ; Gestation and lactation in relation to 
 growth, 261 ; The Missouri experiments, 262. 
 
 CHAPTER XIV 
 The Practice of Breeding . . . . . . 280-303 
 
 Improvement in size, 263; Improvement in function, 
 264 ; The milking function, 265 ; Improvement in wool 
 production, 266 ; Improvement in tendency to lay on fat. 
 
TABLE OF CONTENTS xiii 
 
 267 ; Improvement in speed, 268 ; Selection, 269 ; Natu- 
 ral selection, 270 ; Methodical selection, 271 ; Im- 
 portance of selection in animal-breeding, 272 ; Aids to 
 selection, 273 ; The real results of selection in the im- 
 provement of the domestic animals, 274; Selection 
 within pure lines, 275 ; Vilmorin's pure line wheat- 
 breeding, 276 ; Selection most useful when genetic fac- 
 tors are not pure, 277 ; Pure line theory not opposed to 
 improvement by selection, 278 ; Pedigree, 279 ; Regis- 
 tered breeding animals, 280 ; Registry associations, 281 ; 
 Community breeding, 282 ; Importance of numbers, 
 283 ; Selecting the best, 284 ; Selecting chance varia- 
 tions, 286 ; The Burbank method, 286 ; The mendelian 
 method, 287. 
 
ILLUSTKATIONS 
 
 FIG. 
 
 1. Cell division. Prophases. Aftei* Wilson 
 
 2. Cell division. Later phases. After Wilson 
 
 3. The ovarian egg 
 
 4. Human spermatozoa .... 
 
 6. Genital organs of boar. After EUenberger 
 
 6. Sections through ovary of rat 
 
 7. Genital organs of mare. After EUenberger 
 
 8. Genital organs of cow. After EUenberger 
 
 9. Genital organs of sow. After EUenberger 
 
 10. Genital organs of bitch. After EUenberger 
 
 11. Normal presentation in mare 
 
 12. Posterior presentation . 
 
 13. Abnormal anterior presentation . 
 
 14. Abnormal posterior presentation . 
 
 15. Abnormal transverse presentation 
 
 16. Diagram illustrating mendelian inheritance 
 
 17. Diagram illustrating mendelian inheritance 
 
 PAGE 
 
 9 
 11 
 13 
 14 
 21 
 25 
 26 
 29 
 30 
 32 
 76 
 77 
 78 
 78 
 79 
 140 
 145 
 
 PLATE 
 I. 
 II. 
 III. 
 
 IV. 
 
 V. 
 
 VI. 
 
 PLATES 
 
 Genital organs of mare. After EUenberger 
 Superfcetation in mare .... 
 Upper : A mare mule that secretes milk . 
 Lower : A Free-Martin heifer . 
 Unusual fertility in a cow. Triplet calves 
 Normal healthy uterus of sow . 
 Uterus of sterile sow 
 
 FACING PAGE 
 
 . 43 
 
 
 62^ 
 
 
 84^, 
 
 
 84^ 
 
 
 . 108 
 
 
 118 ' 
 
 
 119 *^ 
 
 XV 
 
XVI 
 
 ILLUSTRATIONS 
 
 PLATE FA{ 
 
 VII. Upper: Steer fed ration not restricted 
 
 Lower : Steer fed greatly restricted ration 
 VIII. Upper : Steer fed ration not restricted 
 Lower : Steer fed for normal growth . 
 IX. Upper : Steer fed generously, at age 120 days . 
 Lower : Same at age 27 months .... 
 X. Upper : Dam of seven mule foals followed by filly foal 
 
 Lower : Filly foal born after seven mule foals . 
 XL Upper : Eleventh foal following ten mule foals . 
 Lower : Dam of ten mule foals and their filly foal 
 XII. Upper : Ninth foal following eight mule foals . 
 
 Lower : Foaled after eight mule foals in succession 
 
 XIII. Upper : Twelfth foal following eleven mule foals 
 Lower : Mother of eleven mule foals and their horse 
 
 foal 
 
 XIV. Upper : Close in-breeding of fox terrier 
 Lower : Eighth generation of intense in-breeding 
 
 XV. In-bred Berkshire ...... 
 
 XVI. Cross-bred Hereford-Aberdeen Angus steer 
 XVII. Upper: Half-blood buffalo (bison) heifer . 
 
 Lower : Cross-bred buffalo-cattle bulls 
 XVIII. Upper : A five-year-old hinny .... 
 
 Lower : Sheep-goat hybrid ..... 
 
 XIX. Effect of food supply on development. Side view 
 
 XX. Same. Front view 
 
 XXI. Effect of starvation on capacity to grow 
 XXII. Recovery from starvation 
 
 XXIII. Upper : Cow fed corn products .... 
 Lower : Calf from cow fed corn products . 
 
 XXIV. Upper : Cow fed wheat products 
 Lower : Calf from cow fed wheat products 
 
 XXV. Permanent effect of retarded growth . 
 
 XXVI. Grace Briggs at age 18 years .... 
 
 XXVII. Duchess Skylark Ormsby 
 
 XXVIII. Sophie 19th of Hood Farm 
 
 XXIX. Daughters of the same sire ..... 
 
 XXX. Three generations showing impressive character of 
 original dam ...... 
 
 XXXI. Result of using a pure-bred sire .... 
 
 XXXII. Result of using a scrub sire .... 
 
ACKNOWLEDGMENTS 
 
 The author is indebted to R. Pearl for Plate IV, to 
 J. W. Connaway for Plates V and VI, to P. F. Trow- 
 bridge for Plates VII, VIII, IX, XXI, XXII, and XXV, 
 to E. A. Trowbridge for Plate XVI, to M. Boyd for 
 Plate XVII, to L. Monsees for Plate XVIII upper, to 
 W. J. Spillman for Plate XVIII lower, to Hart et al, 
 for Plates XXIII and XXIV, to C. H. Eckles for 
 Plates XXVI, XXIX, and XXX, and to H. Hackedorn 
 for Plates XXXI and XXXII. 
 
 Grateful acknowledgment is made to all these persons 
 for their valuable assistance. 
 
 XVll 
 
THE BREEDING OF ANIMALS 
 
 CHAPTER I 
 THE CELL 
 
 The greatest modern contribution to the science of 
 animal-breeding was the formulation of the so-called 
 cell theory. This fundamental biological generalization 
 ranks with the evolution theory in importance in many 
 respects ; it has given a definite physical basis for in- 
 heritance. 
 
 1. The cell theory. — All the higher forms of life are 
 made up of cell units, and from these all parts of the 
 body are constructed. Although various in form, all 
 living cells are alike in having within a mass of proto- 
 plasm which Huxley called the '' physical basis of life." 
 In the simple one-celled forms all functions are found in 
 the one cell, but in the more complex higher forms a 
 physiological division of labor results in the distribution 
 of functions among the cells. ''It is to the cell," says 
 Verworn,^ '' that the study of every bodily function 
 sooner or later drives us. In the muscle cell lies the 
 problem of the heart beat and that of muscular con- 
 traction ; in the gland cell reside the causes of secretion ; 
 in the epithelial cell, in the white blood cell, lies the 
 problem of absorption of food, and the secrets of the 
 
 1 Wilson, " The Cell," p. 6, 1911. 
 
 B 1 
 
2 THE BREEDING OF ANIMALS 
 
 mind are hidden in the ganglion cell." It is now clearly- 
 apparent that the great questions of reproduction, in- 
 heritance and development, involving as they do the 
 problems of embryology and evolution, are intricately 
 bound up with the structure and functions of the cell. 
 
 2. The germ-cells. — The heritage of the species is 
 contained within the germ-cell. The microscopic egg of 
 the female carries within its minute structure the germ 
 characters of all the maternal ancestors. The germ-cell 
 of the male, the spermatozoon, holds within its exceed- 
 ingly minute compass the sum total of all the heritable 
 characteristics of the paternal ancestors. All cells are 
 derived from other cells. Virchow's claim made in 1855 
 that every cell must have been formed by cell division 
 from some previously formed cell, has now been definitely 
 established. Not only does growth and development 
 take place by cell division in the fertilized egg-cell, but 
 the egg-cell itself is directly derived by cell division from 
 an egg-cell of the immediately preceding generation, and 
 so on indefinitely. 
 
 3. The cell. — The cell is a mass of protoplasm con- 
 taining a nucleus, and both nucleus and protoplasm arise 
 through division of the corresponding elements of a pre- 
 existing cell.^ 
 
 The word cell is derived from the Greek and means a 
 hollow chamber. The term came into common use be- 
 fore the form and structure of the cell were well under- 
 stood. The cell-wall which is characteristic of most 
 cells is not an essential part of its structure. It is also 
 
 1 Wilson, "The Cell in Development and Inheritance," p. 19, 
 1906. 
 
 Ley dig, " Lehrbuch der Histologie," p. 9, 1857. 
 Schultze, "Arch. Anat. u. Phys.," p. 11, 1861. 
 
THE CELL 3 
 
 true that living cells are never hollow chambers, but are 
 filled in whole or in part by a colorless, viscid, semi-fluid 
 substance, protoplasm. Many cells are simply masses 
 of protoplasm lacking entirely any kind of an enclosing 
 wall. Lying within the protoplasm is a minute body of 
 spherical form which is the cell nucleus. These two, 
 the protoplasm and the nucleus, are of universal occur- 
 rence and are the essential components of a living cell. 
 
 4. Is the cell the physiological unit ? — A study of the 
 form and function of the cell leads to the inevitable 
 conclusion that in a very real sense the cell is the mor- 
 phological unit of the organism. In its physiological 
 relations to the cells* of the body as a whole, however, 
 it is not to be regarded as an independent unit but rather 
 as a localized center of bodily activities. The individual 
 cell in a multicellular body is influenced, sometimes in 
 a marked degree, by the surrounding cells. The most 
 fundamental problem in growth and development of 
 animals is what and how much influence do the body- 
 cells of one group have over the cells of another group. 
 Is there a physiological connection between adjoining 
 cells? Can a group of cells forming a so-called system 
 like the reproductive system in the animal body be in- 
 fluenced by the soma or body-cells ? If influenced at all, 
 can such influence have any effect upon the germ plasm 
 in the nucleus of the germ-cell ? Is it probable that the 
 germ characters may be changed by these influences so 
 that the offspring of the parent bodies where these in- 
 fluences have been at work, will correspond in any way 
 to the changes occurring in the parent body? In other 
 words, are acquired habits transmitted ? It is to be re- 
 gretted that the microscopic study of the cell has thrown 
 little light upon this fundamental question. As indicated 
 
4 THE BREEDING OF ANIMALS 
 
 above, the cell in the animal body is in more or less close 
 physiological relation with the other cells of the body, 
 but these relationships and their bearings upon- the 
 fundamental facts of biology have not yet been clearly 
 determined. 
 
 5. The structure of the cell. — The cell contains a 
 cell-body and the nucleus. The cell-body is all that 
 portion of the protoplasm not contained in the nucleus. 
 The cell in its simplest form is a rounded mass of proto- 
 plasm. This type is found generally in one-celled forms 
 and is the characteristic form of the egg-cell of the higher 
 animals. The fact that the form of cells in the higher 
 plants and animals is not always* rounded spherical is 
 due to unequal pressure and the movement of the cells 
 comprising the body. 
 
 The nucleus is a definite, clearly-marked body existing 
 within the protoplasmic contents of the living cell, and 
 its relation to growth, reproduction and heredity have 
 given it a commanding position in the study of modern 
 biological problems. Other bodies are often found in 
 the cell, such as food granules, products of excretion, 
 fat globules and crystals. None of these plays an active 
 part in the metabolism of the cell and may be regarded 
 as accidental or at least subsidiary to the major role 
 played by the protoplasm itself. Another body generally 
 found in the cell is the centrosome which is concerned 
 with the mechanism of cell division. The cell-wall is 
 generally present in the higher forms of plant and animal 
 life and consists of a membrane which is usually lifeless. 
 
 6. Protoplasm. — The protoplasm is universally present 
 in every living cell. It is the most fundamentally impor- 
 tant life substance. Huxley aptly designated protoplasm 
 as " the pltysical basis of life." It is not to be regarded 
 
THE CELL ' 5 
 
 as being a definite chemical substance, as its composition 
 changes. It is a viscid, colorless, semifluid material 
 having a higher index of refraction than water, and hence 
 appears brighter. It was called slime by Schleiden. 
 The protoplasm of the cell has a definite structural 
 arrangement appearing as a meshwork, or reticulum, and 
 a ground substance, or cell-sap, filling the intervening 
 spaces. In addition to these two definite substances 
 there are present in the protoplasm minute granules 
 or microsomes which are distributed regularly or irregu- 
 larly along the lines of the meshwork. While other 
 materials are often found in the protoplasm, the above 
 materials are regarded as the essential elements of pri- 
 mary importance in the activities of the cell. 
 
 7. The nucleus. — The nucleus is the center of the 
 constructive activities of the cell. When the nucleus is 
 destroyed, those processes which result in the growth 
 and development of the organism can no longer take 
 place. Only destructive activities are possible in a cell 
 devoid of a nucleus, and these can go forward for only a 
 limited time. " The nucleus is generally regarded," says 
 Wilson, '' as a controlling center of cell activity, and hence 
 a primary factor in growth, development and the trans- 
 mission of specific qualities from cell to cell, and from 
 one generation to another." ^ Growth is the result 
 of cell division, and the impetus for cell division appears 
 to come from the nucleus. The essential fact in cell 
 division is that a portion of the nuclear material of the 
 parent cell shall pass into the new cell. The new cell 
 in its turn becomes a parent cell, and so the process of 
 growth continues. The nucleus is typically spherical 
 and moves freely within the cell. It exhibits two distinct 
 
 1 Wilson, "The Cell in Development and Inheritance," p. 30. 
 
6 THE BREEDING OF ANIMALS 
 
 phases which result from the varying degrees of activity 
 present in the nuclear substance. One phase may be 
 designated as the vegetative or quiescent stage and the 
 other the active stage which is characteristic of that 
 period in the development of the nucleus when the many 
 complicated and significant changes occur which result 
 in cell division and in reproduction. 
 
 The typical nucleus during the vegetative stage pos- 
 sesses certain distinct structural forms which are con- 
 cerned in the many important nuclear activities: (1) 
 The nuclear wall which encloses the nucleus and dif- 
 ferentiates the nucleus from the cell-body; (2) The 
 reticulum, which is the primary factor in nuclear activities, 
 and appearing as an irregular network. The reticulum 
 in turn comprises two structures, the linin and the chro- 
 matin. The latter is undoubtedly the most fundamentally 
 important organic substance concerned with the growth, 
 development and inheritance of plants and animals. 
 It is apparently the only or chief material which is trans- 
 mitted from the parent cell to the new or daughter cell 
 by division, and from it all nuclear substance may be re- 
 formed. The word chromatin is given to this material 
 because it becomes deeply stained upon the addition of 
 certain well-known reagents. The chromatin may appear 
 in the cell in scattered granules, varying in size and form, 
 or in a single deeply staining mass, but more often the 
 arrangement of the chromatin in the nucleus resembles 
 a network which is closely associated with the clearly 
 differentiated linin. (3) The nucleoli are generally but 
 not always present, and their nature and functions are 
 not well understood. By some authorities the nucleoli 
 are the by-products of the activities going on in the 
 nucleus. (4) The ground substance is a fluid filling 
 
THE CELL 7 
 
 the chromatin network and is not stained by ordinary 
 reagents. 
 
 8. Growth by cell division. — How does growth take 
 place in a living organism? What are the primary 
 factors concerned in the increase in size? What changes 
 in the organism result in the progressive development 
 of the many useful qualities found in the improved types 
 of the domestic animals? How does a microscopic egg- 
 cell develop into a mature and highly organized animal 
 possessing countless cells of many different forms and 
 exercising various and important functions? A still 
 more fundamental problem, if possible, is, how are the 
 qualities of an individual transmitted from parent to 
 offspring? What is the physical basis of heredity and 
 what are the elements concerned in a study of inheritance ? 
 
 Many of these questions are answered by a study of 
 the cell and specifically by a study of cell division. The 
 entire tissue structure of the animal body arises by re- 
 peated division from the germ-cell. The germ-cell itself 
 is the result of the division of a cell which formed 
 a part of the body of the parent. Thus it is that the 
 germ substance carrying the hereditary material is 
 separated from the parent body by cell division. The 
 fertilized egg by continued cell division passes on to every 
 cell in the body a portion of its own substance. The 
 process of cell division must therefore be regarded as a 
 great fundamental fact in the growth and development 
 of plants and animals as well as one of the most significant 
 and primary facts in the transmission of qualities from 
 parent to offspring. 
 
 Growth occurs as the result of continued cell division 
 rather than by any material increase in the size of exist- 
 ing cells. 
 
8 THE BREEDING OF ANIMALS 
 
 9. How cells divide. — All cells do not divide in the 
 same manner, but the most typical process is known as 
 indirect division or mitosis, and this will be here described. 
 We have seen that the nucleus contains within its minute 
 compass the active material which stimulates the cell 
 to various activities and determines its physiological 
 destiny. If further evidence was needed on this point, 
 it would be found in the remarkable and interesting trans- 
 formations which take place within the nucleus before 
 and during the process of cell division. 
 
 The cell first passes through a vegetative or quiescent 
 stage, and this is followed by a period of activity finally 
 resulting in the formation of two cells from the original 
 parent cell. Various clearly marked stages or phases 
 are distinguishable in this process which have been accu- 
 rately described by Wilson. The phases observed are 
 for convenience named : (1) prophase, (2) metaphase, 
 (3) anaphase, and (4) telophase. 
 
 10. Prophase (Fig. 1). — In the vegetative stage the 
 chromatin of the nucleus exists in the form of a network. 
 Generally during the prophase the chromatin loses its 
 net-like arrangement and assumes the form of a skein 
 like thread known as the spireme. During this stage 
 the spireme thread stains intensely and is fine and closely 
 convoluted. It gradually becomes thicker and the con- 
 volutions become more open, giving rise to the '' open 
 spireme." Gradually the spireme breaks up into a num- 
 ber of definite straight or curved rods known as chromo- 
 somes. It is usual for the wall of the nucleus to disappear 
 during this phase, and the chromosomes then lie naked 
 in the protoplasm of the cell. It is a significant fact that 
 every plant and animal possesses a characteristic number 
 of chromosomes and that this number is always even. 
 
Fig. 1. — Cell division. Diagram showing typical prophases in cell 
 division. A, Vegetative or resting stage showing nucleus. B, The 
 spireme thread. C, Preparation for division. D, Formation of chro- 
 mosomes. E, Gradual fading of nuclear membrane. F, Chromosomes 
 in equatorial plate ready for division. 
 
 9 
 
10 THE BREEDING OF ANIMALS 
 
 In the ox and in man the number is sixteen. The fact 
 that the number of chromosomes is even in all species is 
 due to the fact that during the processes of fertilization 
 one-half the chromosomes are derived from the female 
 and one-half from the male parent. 
 
 After the breaking up of the spireme thread into a 
 definite number of chromosomes, there is formed in the 
 cell the so-called amphiaster. The development and 
 activities of this interesting structure seem to be for the 
 purpose of arranging the chromosomes in position for 
 division. All the processes concerned in the prophases 
 are preparatory to the final division, and ultimate dis- 
 tribution of chromatin to the new cell. 
 
 11. Metaphase. — Each chromosome now splits into 
 two exactly equal halves and the two new groups move 
 to opposite sides of the cell. The chromosomes divide 
 lengthwise, and by so doing there results an accurate 
 division of the chromatin into two precisely equivalent 
 portions. Each portion eventually becomes the nucleus 
 of one of the two new daughter cells which result from 
 this division. The most fundamentally important fact 
 about this division of the chromatin is that it is a qualita- 
 tive as well as a quantitative division. There is much evi- 
 dence to show that the spireme thread (and, therefore, 
 the chromosomes) is composed of granules or units 
 throughout its length, and each of these units represent^ 
 a definite character or set of characters in the individual. 
 It follows that when a lengthwise division occurs, these 
 units are divided and a portion of each is passed on to the 
 daughter cells (Fig. 2). 
 
 The arrangement of the chromatin in the spireme, its 
 breaking up into chromosomes, and the splitting of the 
 latter into halves are all directed toward the accurate 
 
THE CELL 
 
 11 
 
 Fig. 2. — Diagram of later phases of cell division. G, Splitting of 
 the chromosomes. H, Daughter chromosomes diverging to form new 
 cells. 7, Chromosomes grouped in daughter nuclei, final changes before 
 complete division. /, The two new cells. 
 
 division of the smaller chromatin granule (chromo- 
 mere or id as designated by Weismann). In this process, 
 therefore, we have a reasonable physical basis for a better 
 understanding of the transmission of characters from 
 
12 THE BREEDING OF ANIMALS 
 
 parent cell to daughter cell and thus from parent to off- 
 spring. 
 
 12. Anaphase. — The essential step in the anaphase 
 is the separation of the two groups of chromosomes which 
 were derived from the splitting of the chromosomes of 
 the parent cell. These pass to opposite sides of the cell, 
 and in many forms these new groups begin at once to 
 assume the appearance of the original nuclear material. 
 
 13. Telophase. — Complete division of the cell is 
 finally accomplished by constriction of the parent cell- 
 walls and the formation of a new membrane w^hich encloses 
 the two daughter nuclei each in its own cell. The two 
 groups of chromosomes derived from the parent nucleus 
 are rearranged and become the nuclei of the new daughter 
 cells which in their turn may pass through all the stages 
 described above. 
 
 The essential steps, then, in cell division are : (1) The 
 formation of the spireme thread from the chromatin 
 and its division into chromosomes; (2) The splitting of 
 the chromosomes through the middle longitudinally; 
 (3) The movement of the divided portions of the chromo- 
 somes to the new or daughter cells. 
 
 14. The germ-cells in detail. — In all the higher forms 
 of animals, reproduction is accomplished by the forma- 
 tion of special reproductive cells called the germ-cells. 
 The germ-cells are the product of the reproductive group 
 of cells and are endowed with peculiar powers not gen- 
 erally possessed by the soma- or body-cells. Weismann 
 divided the cells of the body into two very clearly marked 
 and distinct groups, the soma- or body-cells and the germ- 
 cells. The soma-cells are primarily concerned with the 
 individual life of the animal, while the germ-cells are 
 destined solely for the purpose of reproduction. The 
 
THE CELL 
 
 13 
 
 germ-cells have no important relation to the functional 
 activities which are especially concerned with the indi- 
 vidual existence of the animal. They are clearly in- 
 tended for ultimate separation from the individual and 
 destined to provide for the continuance of the species. 
 In some lower forms of life, the body-cells and germ-cells 
 are not so clearly separated, but in the domestic animals 
 such differentiation is characteristic. The male germ-cell 
 is called the spermatozoon or sperm-cell, and the female 
 germ-cell the egg or ovum. 
 
 15. The ovum. — The germ-cell of the female is the 
 egg or ovum (Fig. 3). It is one of the largest cells in the 
 animal body. It is spheroidal in 
 shape and contains a nucleus or 
 germinal vesicle and within the 
 nucleus a nucleolus or germinal 
 spot and a large amount of pro- 
 toplasm (cytoplasm) surrounding 
 the nucleus. In the protoplasm 
 are often distributed numerous 
 masses of material or yolk, the 
 function of which seems to be 
 chiefly to nourish the fertilized 
 egg-cell. The nucleus of the 
 ovum during the quiescent stage lies near the center of 
 the cell, but gradually moves toward the cell-wall as the 
 egg becomes more mature. During the final stages in the 
 development of the egg, the nucleus loses a large part of 
 its chromatin. This process is called maturation and re- 
 sults ultimately in reducing the number of chromosomes to 
 one-half the number characteristic of the species. This 
 process is preparatory to the fertilization of the egg by 
 the spermatozoon. During fertilization, the chromo- 
 
 
 '^ 
 
 ^m 
 
 Fig. 3. — The 
 
 egg. A, nucleus ; 
 plasm. 
 
 ovarian 
 B, cyto- 
 
14 
 
 THE BREEDING OF ANIMALS 
 
 somes of the egg-cell unite with those of the sperm-cell 
 and a new nucleus is thus formed which becomes the 
 active center of the new daughter cell. 
 
 16. The spermatozoon. — The male germ-cell or sper- 
 matozoon is exceedingly minute and its investigation cor- 
 
 FiG. 4. — Human spermatozoa (greatly magnified), a, acrosome; 
 h, nucleus ; c, end knob ; d, middle piece ; e, tail ; /, end piece ; g, axial 
 filament. 
 
 respondingly difficult. Although early discovered, its 
 significance was not clearly determined until 1865 when 
 Schweigger-Seidel and St. George discovered that the 
 sperm was a cell and contained a nucleus, cytoplasm and 
 all the essential elements of a perfect cell. The function 
 of the sperm-cell is to fertilize the egg and thus provide 
 
THE CELL 15 
 
 for the reproduction of the species. The spermatozoon 
 in its gross anatomy has the semblance of a very minute 
 tadpole swimming freely about in liquids. It has a 
 distinct head piece and a long slender tail piece or cilium. 
 (See Fig. 4.) When closely examined, the sperm-cell 
 exhibits all the essential characteristics of a typical cell, 
 'with a nucleus, cytoplasm and a cell-wall. This cell is 
 so small that in some forms it is but i o oVo o ' of the size 
 of the egg-cell. The nucleus occupies almost the entire 
 space available in the head piece, being surrounded by 
 a very thin layer of cytoplasm between it and the cell- 
 wall. The tail of the sperm-cell is joined to the head 
 piece by the middle piece. It is of cytoplasmic origin 
 and possesses the power of motion. This ability to propel 
 itself forward in liquid media seems to be in a way an 
 insurance that the sperm-cell will ultimately approach 
 the egg-cell for the purpose of fertilization. 
 
 The power of motion is retained by the spermatozoon 
 for a considerable time under favorable conditions of 
 warmth and moisture. After the sperm enters the egg, 
 it loses the power of motion and the tail piece is absorbed. 
 
 The essential portions of the sperm which are concerned 
 in the process of fertilization are the nucleus and the 
 middle piece. Other structures which are accessory to 
 these are the apex by which the sperm attaches itself 
 to the ovum and the tail whose functions have already 
 been described. 
 
CHAPTER II 
 REPRODUCTION 
 
 The value of a breeding animal is measured by its 
 own individual character, its ability to transmit desir- 
 able characters to its offspring, and by its prolificacy. Of 
 two animals of equal individuality and inheritance, the 
 one capable of producing numerous and vigorous offspring 
 will be the more valuable. The subject of reproduction 
 in animal-breeding is therefore of great importance and 
 second only to inheritance in estimating animal values. 
 
 Two methods of reproduction are common among 
 plants and animals, asexual and sexual. These differ 
 greatly in form and method but accomplish the same 
 ultimate result, which is the continuance of the race. 
 
 17. Asexual reproduction. — The asexual method of 
 reproduction is common among the simplest forms of 
 plant and animal life. It is a process of cell division 
 or fission which varies in different forms, but in its most 
 elementary manifestations it is simple cell division. In 
 unicellular forms the cytoplasm of the cell and the nucleus 
 divide into two equal parts and each half becomes a 
 perfect new individual. Each new cell increases in bulk 
 by the absorption of food and in turn becomes a parent 
 cell and reproduces by division as before. A similar 
 form of reproduction is found in the developing embryo 
 of mammals and of the other body-cells. The tissues of 
 
 16 
 
REPRODUCTION 17 
 
 the body thus formed cannot, however, continue to divide 
 indefinitely, but sooner or later reach their full develop- 
 ment and do not thereafter increase in bulk by further 
 division. 
 
 18. Sexual reproduction. — Reproduction in the higher 
 forms of organic life is a complicated process and is ac- 
 complished by the activities of a special group of cells 
 which is called the reproductive or generative system. 
 These germ-cells are highly specialized, and their develop- 
 ment and functions divide the individuals of a species 
 into two sexes, male and female. The two sexes differ 
 widely in form and characters, but particularly in respect 
 to their physiological relations to reproduction. The 
 product of the male. germ-cells is the spermatozoon, an 
 exceedingly small cell but carrying in its minute substance 
 the inherited potentialities of its ancestors. The female 
 germ-cell or ovum similarly derived from the female is 
 much larger, but also carries the germ substance which 
 later, after fertilization by the spermatozoon and under 
 proper conditions, will become a new individual. 
 
 19. The reproductive process. — The essential fact 
 in the reproductive processes of all vertebrate animals 
 is the formation of an egg or ovum by the female and of a 
 fecundating fluid containing the spermatozoon or sperm- 
 cell by the male. The union of the two germ-cells is the 
 first step in the independent existence of the new indi- 
 vidual. The conjugation of the egg and spermatozoon 
 sets in motion a series of events which, whether viewed 
 from the standpoint of racial significance or of biological 
 interest, has no parallel in the whole realm of biology. 
 Upon the successful development of the fertilized egg- 
 cell depends the future of the species. The union of the 
 egg and spermatozoon takes place in some forms outside 
 
18 THE BREEDING OF ANIMALS 
 
 the body of the female. In fishes, the spawn con- 
 taining the eggs is deposited in the water by the female, 
 and the fertilizing fluid of the male containing the sper- 
 matozoa is also deposited in the water on or near the female 
 spawn. In all higher animals, including the domestic 
 animals, the fecundating fluid of the male reaches the 
 egg inside the body of the female, and the process of ferti- 
 lizing the egg is accomplished within the generative organs 
 of the female. 
 
 20. Oviparous animals. — In some species of animals, 
 including birds, fishes, most reptiles, and nearly all 
 invertebrates, the eggs are deposited outside the body 
 either before or after fertilization. In the bird family, 
 which includes all the domestic fowls, the egg is fertilized 
 inside the body of the mother, where it undergoes some 
 slight development before being eventually deposited or 
 laid outside the body of the female. Animals of this 
 class are called oviparous, to distinguish them from vivip- 
 arous forms which bring forth their young alive. The 
 future development of the egg deposited by oviparous 
 animals is dependent upon its being supplied with favor- 
 able conditions of heat and moisture. This period of 
 development outside the body is called the period of 
 incubation and is, in many ways, similar to the period 
 of gestation in viviparous animals. Animals in which 
 the fertilized egg develops inside the body are called vivip- 
 arous, and this development proceeds to a point where 
 the young animal is, in the main, able to carry on a sepa- 
 rate and independent existence. The period of growth 
 inside the body of the mother in mammalian animals is 
 called the period of gestation, and during this period 
 the developing embryo is gradually fitted for an inde- 
 pendent life outside the protecting body of the mother. 
 
REPRODUCTION 19 
 
 21. Primary and secondary sexual characters. — 
 
 The particular characteristics which differentiate the 
 male from the female sex may be divided into primary 
 and secondary characters. The primary characters are 
 those which are peculiar to the sex. In the male, the 
 form and functions of the generative organs clearly 
 differentiate him from the female. As Lee ^ has pointed 
 out, the function of the primary sexual characters of 
 the male is the production of spermatozoa and the im- 
 pregnation of the female Qgg. The activities of the 
 primary sexual organs of the female center about the 
 production of the egg and the development of the 
 embryo. 
 
 The secondary sexual characters are those which may 
 often be possessed in common by both sexes but experi- 
 ence a special and somewhat different development in 
 the two sexes. Examples of secondary sexual characters 
 are the horns of the ram in some breeds of sheep, the 
 spurs of the cock, the tusks of the boar, the various col- 
 ored plumage of many male birds, and the crest in stal- 
 lions and bulls. Under certain conditions, the secondary 
 sexual characters which are in general characteristic of 
 the male sex alone may be developed in the female. Thus, 
 hens sometimes develop spurs and ewes develop horns. 
 
 Castration of the male causes a check in the develop- 
 ment of the secondary sexual characters and causes the 
 male to approach more nearly to the form and appear- 
 ance of the female. 
 
 22. The reproductive organs of the male (Fig. 5). — The 
 organs of generation in the male are : (a) the testicles, cor- 
 responding to the ovaries in the female ; {h) vasa def erentia, 
 or the ducts leading from the testicles to the ejaculatory 
 
 1 "American Text Book of Physiology," 1903, p. 443. 
 
20 THE BREEDING OF ANIMALS 
 
 duct; (c) vesiculse seminales; {d) prostate glands; {e) 
 Cowper's gland ; (/) urethra*, through which the urinary 
 and genital secretions are conveyed ; {g) the penis, 
 through which the semen of the male is conveyed to the 
 female genital organs. The secretions of the vesiculse 
 seminales, the prostate, and the Cowper's gland all empty 
 into the urethra, where they mix with the seminal fluid 
 from the testicles. The testicles, vasa deferent ia and 
 urethra and penis are often called the essential organs of 
 generation, while the remaining three are referred to as 
 the accessory organs. 
 
 23. The testicles. — The essential sexual elements, 
 the spermatozoa, are formed in the testicles. The removal 
 of the testicles, therefore, destroys the ability of a male 
 animal to elaborate the male germ-cells and permanently 
 destroys his fecundity. The structure of the testis is 
 described in some detail by Marshall as follows : ^ '' This 
 organ is enclosed within a fibrous capsule, the tunica 
 albuginea, which is very rich in lymphatics. It is cov- 
 ered by a layer of serous epithelium reflected from the 
 tunica vaginalis. Posteriorly the capsule is prolonged 
 into the interior of the testis in the form of a mass of 
 fibrous tissue (the mediastinum testis). Certain other 
 fibrous processes or trabeculse also project inwards from 
 the capsule, and divide the glandular substance into 
 lobules. The efi^erent ducts of the testis (vasa efferentia) 
 open into a single convoluted tube situated at the pos- 
 terior margin of the organ and attached to the medias- 
 tinum. This is the epididymis. Its lower extremity 
 is prolonged into a thick-walled muscular tube (the vas 
 deferens) which is the passage of exit for the seminal 
 fluid or sperm-containing secretion. The glandular sub- 
 
 1 Marshall, "The Physiology of Reproduction." 
 
REPRODUCTION 
 
 21 
 
 Fig. 5. -Genital organs of boar, l^testlcle; 2 epididymis 3, 
 vas deferens; 4, spermatic artery; 5, vesicula semmalis; 6 prostate 
 7 Cowper's gland; 8, bulbo cavernosas muscle; 9, 9 and 9 , penis, 
 10, retractor penis muscle; 12, orifice of preputial pouch. 
 
22 THE BREEDING OF ANIMALS 
 
 stance of the testis is composed of the convohited seminif- 
 erous tubules, two or three of which join together to 
 form a straight tubule which passes into the body of 
 the mediastinum. The straight tubules within the 
 mediastinum unite in their turn, giving rise to a network 
 of vessels called the rete testis. From the rete the vasa 
 efferentia are given off. Between the tubules is a loose 
 connective tissue containing a number of yellow epithelioid 
 interstitial cells. The connective tissue also contains 
 numerous lymphatics and blood-vessels (branches of the 
 spermatic artery). The nerves of the testis are derived 
 from the sympathetic system, but a few filaments come 
 from the hypogastric plexus." 
 
 The male reproductive organs ^ other than the testicles 
 are chiefly concerned in providing for the transmission of 
 the fully mature sperm-cells from the testicles. The 
 seminal fluid is secreted by the seminiferous tubules and 
 after expulsion is mixed with other fluids from the male 
 accessory organs. 
 
 The function of the seminal fluid seems to be to pro- 
 vide a favorable medium for the spermatozoa. 
 
 24. Castration. — The removal of the testicles of the 
 male results in profoundly influencing not only the breed- 
 ing function of the animal but in marked bodily change. 
 While the testicles seem to have no important connec- 
 tion with or relation to the body-cells and their removal 
 interferes in no way with the normal, healthy function- 
 ing of the other bodily organs, it is nevertheless true that 
 castration materially influences the animal economy. 
 
 1 The student is referred to standard works on anatomy and 
 physiology for a detailed discussion of the organization and 
 functional relations of the various male reproductive organs. 
 See Sisson, "Veterinary Anatomy." 
 
 Chauveau, "Veterinary Anatomy." 
 
REPRODUCTION 23 
 
 If the young male is castrated, the external appearance 
 of the animal undergoes a gradual change. The whole 
 aspect becomes less masculine. The shoulders, neck 
 and crest develop relatively to a much less extent. The 
 hind quarters are relatively better developed in the 
 cas|rated animal. The temperament and disposition 
 undergo radical changes. The bull castrated before 
 puberty fails to develop the heavy head and horns, curly 
 hair and protruding eye characteristic of this animal. In 
 swine, castration prevents the development of the shoulder 
 plates and tusks. The horns of sheep are very greatly 
 dwarfed, though the same effect is not so marked in cattle. 
 The removal of the testicles also influences the physiolog- 
 ical constitution of the animal. It is well known that 
 oxen grow larger and heavier than the uncastrated bulls. 
 The same result is observed in capons which often grow 
 to a much greater weight than the normal male. The 
 castration of old boars results in the disappearance of 
 the strong odor characteristic of the flesh, and their food 
 value is thereby increased. 
 
 The removal of the ovaries (spaying) of the female 
 is followed by phenomena similar to those observed in 
 the castrated male. The spayed female loses her feminine 
 appearance and approaches the male in general char- 
 acter. Like the male, the disposition becomes quieter 
 and the general physiological condition of the animal 
 favors more rapid laying on of fat. 
 
 At the Massachusetts Experiment Station, Goodale ^ 
 castrated a brown Leghorn cockerel at twenty-four days 
 old. At the same time the fresh ovaries of two brood 
 sisters were cut in several pieces and placed under the 
 skin of the castrated cockerel. The bird developed in 
 
 1 Goodale, ** Science," Vol. 40 (1914), p. 549. 
 
24 THE BREEDING OF ANIMALS 
 
 every external character like a female, so much so that 
 expert poultry men were deceived. 
 
 We may conclude that the castration of animals is 
 successful in preventing undesirable animals from re- 
 producing, improving the fattening qualities of the meat 
 animals, increasing the size in some cases, improving 
 the quality of the flesh, and increasing the value of draft 
 animals.^ 
 
 25. The reproductive organs of the female (Plate II). — 
 The essential organs of reproduction in the female are 
 the two ovaries. The accessory organs are the Fallopian 
 tubes, the uterus, the vagina, the vulva and the mammary 
 glands. The function of the female organs of generation 
 is the production of the female germ-cells or ova and, 
 when fertilized, to provide nutrition and proper support 
 for the developing embryo. 
 
 26. The ovaries. — The female egg has its origin in 
 the ovary. This organ is composed of connective tissue, 
 blood-vessels, nerves and lymphatics enclosed in an outer 
 covering — the epithelium. A cross-section of the ovary 
 of any mature breeding animal will exhibit a large number 
 of follicles or sacs scattered through its vascular substance 
 (Fig. 6). The latter are small, varying from one-hundredth 
 to one-thirtieth of an inch in size.^ These small sacs are 
 called the Graafian follicles, and each contains an ovum 
 or egg. The eggs or ova in these follicles exhibit various 
 stages of development, some being almost or quite mature, 
 while others are very small and undeveloped. The 
 beginning of the formation of a Graafian follicle is indi- 
 cated by a slight depression in the surface of the ovary 
 which gradually extends into the substance of the ovarian 
 
 1 Pusch, "AUegemeine Tierzucht," 1911, p. 153. 
 
 2 Smith, "Physiology of the Domestic Animals," p. 909. 
 
REPRODUCTION 25 
 
 tissue in the form of a tubule. Eventually this sac 
 becomes constricted at the surface of the ovary until 
 finally the external opening is entirely closed and the 
 tubule becomes a closed follicle within the tissues of the 
 organ. Within the follicle 
 itself, there have been 
 formed, in the meantime, 
 single, large spherical cells 
 (primordial germ-cells) 
 from which one or some- 
 times two ova are devel- .0-~^-:k 
 oped. The part of the t^^^ 
 
 Graafian follicle not OCCU- ^ig. 6. — Sections through ovary 
 
 pied by the ovum is filled of rat, typical of ovarian structure in 
 • ,i n 'A u X mammals. 
 
 With a nuid substance. 
 
 The follicle increases in size and approaches the center of 
 the ovary until near maturity, when it rises to the surface 
 and finally is ruptured, thus liberating the enclosed egg. 
 The bursting of a Graafian follicle and the discharge 
 of the egg is called ovulation. This event is marked 
 by certain phenomena indicating increased sexual activity. 
 It is believed that menstruation or the period of heat in 
 domestic animals is coextensive with the ripening of 
 the egg. It is true, however, that, under some circum- 
 stances, ovulation may occur before or after the period 
 of heat. The ripening of the first Graafian follicle in 
 general marks the beginning of. puberty, but has been 
 known to occur even in infancy. In animals generally 
 ovulation does not occur during pregnancy, but there 
 are numerous exceptions to this rule, as will be described 
 later in the case of some animals which have come in heat 
 and have even conceived again, although pregnant at 
 the time (Fig. 7). 
 
26 
 
 THE BREEDING OF ANIMALS 
 
 Fig. 7. — Genital organs of mare. 1, ovary ; 2, Fallopian tube ; 2', 
 fimbriated end of Fallopian tube ; 3, uterus ; 5, horn of uterus ; 6 and 
 6',^ cervix ; 7, broad ligament of uterus ; 9, vagina ; 10, vulva ; 13 and 
 13', lips of vulva; 14, clitoris; 15, urinary bladder; a, utero-ovarian 
 artery with branches to ovary (a) and uterus (a") ; 6, uterine artery. 
 
REPRODUCTION 27 
 
 Some of the domestic animals do not come in heat 
 while suckling young, while others discharge eggs and 
 undergo the periodical phenomenon of heat as readily 
 during lactation as at any other time. 
 
 27. The Fallopian tubes. — The egg which has been 
 discharged as the result of the processes described above 
 finds its way to the uterus through the Fallopian tubes 
 in mammals or the oviduct in birds. These are small, 
 very crooked canals leading from the ovary to the uterus. 
 This accessory organ is not rigidly joined to the ovary 
 by tissues, but the end nearest the ovary is mostly free 
 to move to different sides of the ovary. The ovarian 
 end of the Fallopian tube is expanded into a fimbriated 
 extension which spreads out not unlike the fingers of the 
 hand. The comparison will be still more exact if we con- 
 ceive of the fingers of the hand as being connected by 
 web-like tissues. 
 
 In many mammals, the tube is lined with cilia which 
 move from the ovary toward the uterus. In normal 
 cases when the egg is discharged from the ovary, the 
 fimbriated expansion of the Fallopian tube clasps the 
 ovary at the point where the Graafian follicle bursts 
 through its walls. The ciliary movement within the tube, 
 assisted by muscular movements of the tube itself, carries 
 the egg from the ovary to the uterus. The time required 
 for the passage of the egg through the Fallopian tube has 
 not been definitely determined for all mammals, but is 
 known to vary from three to eight days. 
 
 The union of the spermatozoon and the egg usually 
 takes place in the Fallopian tube. To accomplish this 
 union, it is necessary for the sperm-cell to pass into the 
 uterus and up into the tube. This it is able to do by 
 reason of its possessing the power of independent motion. 
 
28 THE BREEDING OF ANIMALS 
 
 28. The uterus. — The uterus is a muscular sac con- 
 necting the Fallopian tubes and the vagina in which the 
 development of the fertilized egg is carried forward until 
 expelled from the body of the mother at the time of par- 
 turition (Figs. 8, 9, 10). 
 
 In many mammals the uterus divides into two tubes 
 called horns. Each horn is connected with the corre- 
 sponding ovary by means of the Fallopian tube. 
 
 The portion of the uterus nearest the vagina is some- 
 what constricted to form the cervix or neck of the uterus. 
 The vagina connects the uterus with the external genitals 
 called the vulva. 
 
 29. The mammary glands. — The possession of mam- 
 mary glands whose function is the elaboration of food 
 materials for the young offspring is characteristic of 
 all mammals. These glands are highly developed and 
 functional in the fertile female, but are also present in 
 rudimentary form in the male. In rare cases the rudi- 
 mentary glands present in the male have been known 
 to function. Hayward at the Delaware Experiment 
 Station reports the case of a registered Guernsey bull 
 owned by that institution whose mammary glands 
 were developed to the extent of producing a small 
 amount of milk. Milk has also been produced from 
 the rudimentary mammary glands of male goats and 
 sheep. In man the rudimentaries of males have pro- 
 duced milk at birth and at puberty and in exceptional 
 cases at other times. The number of nipples in a 
 species bears some relation to the normal number of 
 young produced in a litter, and also to the needs of 
 the young animal. The glands are generally arranged 
 in pairs either along the ventral side of the thorax or 
 abdomen. 
 
30 
 
 THE BREEDING OF ANIMALS 
 
 Fig, 9, — Genital organs of the sow. 1, lips of vulva ; 2, clitoris ; 
 3, vulva ; 4, external opening of urethra ; 5, vagina ; 5, cervix ; 6, body of 
 uterus ; 7, horn of uterus ; 7', horn of uterus opened to show interior ; 
 8, Fallopian tube ; 8', abdominal opening of Fallopian tube ; 9, ovaries ; 
 12, urinary bladder. 
 
REPRODUCTION 31 
 
 30. Structure of mammary glands.^ — The mammary 
 glands are made up of lobes which in turn are further 
 divided into lobules. The latter arise from secretory 
 alveoli. The lobule is chiefly connective tissue binding 
 together the milk ducts. The alveoli unite together 
 to form the lactiferous ducts which open externally. 
 These ducts are provided with reservoirs w^herein the 
 milk is accumulated during the period of active lac- 
 tation. During lactation the alveoli secrete milk. This 
 secretion goes forward at all times, but is particularly 
 active during suckling. The milk drawn first is of 
 poorer composition in respect to solids than that drawn 
 near the end of the milking. This may be due to the 
 fact that the larger globules pass through the ducts 
 with greater difficulty and are thus retained longer in 
 the gland. 
 
 The processes concerned in milk secretion are not 
 entirely understood, at least three views having been 
 held. One hypothesis is that the secretory cells them- 
 selves break down and thus set free their contents as is the 
 case with the sebaceous glands. Another view^ is that 
 the milk is simply excreted from the cell without causing 
 the breaking down of the cell, in a manner similar to 
 that which occurs in many secretory glands. 
 
 " The third theory ^ was first suggested by Langer, 
 and has since been adopted, with various slight modifi- 
 cations, by Heidenhain, Steinhaus, Brouha and others. 
 According to their view the cells of the gland lengthen 
 out, so that their ends come to project freely into 
 the lumina of the alveoli. The projecting portions 
 then undergo a process of disintegration before or after 
 
 1 Marshall, "The Physiology of Reproduction," p. 553. 
 
 2 lUd., p. 560. 
 
c 
 
 Fig. 10.— Genital 
 organs of bitch, a, 
 ovarian bursa ; b, 
 opened to show ova- 
 ry ; c, ovary ; d, d, 
 horns of uterus ; e, e', 
 body of uterus ; /, 
 neck of uterus; /', 
 cervix (os uteri) ; g, 
 vagina ; i, vulva ; k, 
 opening of urethra ; 
 I, urinary bladder ; 
 m, urethra ; n, n, lips 
 of vulva ; p, clitoris. 
 Vulva, vagina and 
 uterus cut open to 
 show interior. 
 
 2" 
 32 
 
REPRODUCTION 33 
 
 becoming detached, and the cell substance passes into 
 solution to form the albuminous and carbohydrate con- 
 stituents of the milk. The fat droplets which collect in 
 the disintegrating part of the cell give rise to the milk 
 fat. The basal portions of the cell remain in position 
 without being detached, and subsequently develop fresh 
 processes, which in their turn become disintegrated. It 
 is believed, however, that some cells simply discharge 
 their fat droplets and other contents into the lumina, 
 while otherwise remaining intact." 
 
 31. Fertilization of the ovum. — We have seen how 
 growth may continue for a long period by successive 
 cell division. Indeed, in many of the simpler forms, 
 Wilson has pointed out that " as far as we can see from 
 an a 'priori point of view, there is no reason why, barring 
 accident, cell division should not follow cell division in 
 endless succession in the stream of life." ^ 
 
 In some of the very simplest forms, no sexual union 
 has so far been discovered. But, under normal conditions, 
 reproduction without sexual union is rare and practically 
 unknown in the higher animals. The impetus to growth 
 and cell division is not permanent and must be constantly 
 renewed. The stimulus to renewed growth is accom- 
 plished by the definite mixture of living protoplasm from 
 two entirely distinct individuals. This process of fertili- 
 zation involves a union of the ovum of the female and 
 the spermatozoon of the male. This union is the begin- 
 ning of the life of each individual and results not only 
 in energizing the protoplasm of the germ-cell, causing it 
 to divide and grow, but the admixture of germ material 
 from two different individuals introduces into the new 
 organism two distinct lines of inheritance. 
 
 1 Wilson, "The Cell." 
 
34 THE BREEDING OF ANIMALS 
 
 32. The nature of fertilization. — The essential na- 
 ture of fertihzation still remains a matter of discussion. 
 It may be that the fertilization of the egg is primarily 
 a rejuvenescence of the protoplasmic material which, for 
 some at present unknown reason, has lost the power of 
 further growth through cell division. This view was 
 held by Butschli, Hertwig, Minot, Engelman and others. 
 Even in the simpler forms of life where anything like 
 sexual union is absent, the cycle of growth is continually 
 reinaugurated by the conjugation of independent cells. 
 In all higher forms the egg is stimulated to growth and 
 cell division by the introduction of the sperm. 
 
 Weismann has looked upon fertilization as a source 
 of variation and has maintained that this should be 
 regarded as the chief function of this process. Both 
 the theory of rejuvenescence and that which regards 
 this process as chiefly a source of variation are in accord- 
 ance with the observations of practical breeders. Cross- 
 breeding is known to induce greater vigor and increased 
 fecundity and at the same time to break up the fixed 
 characters of the breed or type. It is equally well estab- 
 lished that under certain conditions in-breeding tends to 
 identity of character and results in sterility and weakness 
 of constitution. But, after all, the real purpose and na- 
 ture of sexual union in reproduction is still an unsolved 
 problem. 
 
 33. The process of fertilization. — The ultimate pur- 
 pose of the sexual union of animals is to insure the fertili- 
 zation of the egg by the spermatozoon. When the egg 
 and sperm meet within the generative organs of the fe- 
 male, significant and important changes are set in motion, 
 which eventually result in an admixture or union of the 
 germ substance of the two parents. These changes are 
 
REPRODUCTION 35 
 
 primarily concerned with the nuclei of the egg and the 
 sperm. 
 
 In most species of animals, there is a definite attrac- 
 tion existing between the egg and the sperm-cell, which 
 causes the spermatozoon to attach itself to and finally 
 penetrate the egg. This attraction is probably of a 
 chemical nature. Pfeffer found that solutions of malic 
 acid were as successful in attracting the sperm-cells of 
 ferns as the substance which was thrown off by the female 
 sex cells. In other experiments, other chemical sub- 
 stances have exhibited a specific attraction for the sperm. 
 The seat of this chemical substance which pulls the 
 sperm to the egg seems to be located in the cytoplasm of 
 the egg and not in the nucleus. 
 
 The point at which the spermatozoon enters the egg 
 is often predetermined by the existence of a depression 
 or opening (micropyle) in the wall of the ovum. In 
 some cases, there exists a special protoplasmic attraction 
 cone at which point the sperm enters the egg. The 
 entrance of the sperm in most cases is followed rapidly 
 by the formation of a vitelline membrane which surrounds 
 the egg and prevents the entrance of other spermatozoa. 
 
 Normally in mammals one sperm only enters the egg. 
 When through accident two or more spermatozoa enter 
 the substance of the egg, the developmental changes are 
 abnormal and the daughter nucleus soon dies. 
 
 34. The chromosomes. — When the germ nuclei unite 
 to form the daughter nucleus of the new cell, it seems 
 probable now that the chromatin substance does not fuse 
 in true fashion but the chromosomes may lie side by side 
 within the nucleus of the new cell. It is not definitely 
 determined that these chromosomes remain thus separate 
 and apart throughout the life of the cell, but such may be 
 
36 THE BREEDING OF ANIMALS 
 
 the case. After the reduction of the chromosomes in 
 the maturation of the germ-cells and accompanying the 
 formation of the polar bodies, the number of chromosomes 
 is reduced to one-half the number existing in the body- 
 cells and these uniting with an equal number from the 
 sperm constitute the normal number characteristic of 
 the tissue cells. As Wilson says, " We have thus what 
 must be reckoned as more than a possibility that every 
 cell in the body of the child may receive from each parent 
 not only half of its chromatin substance, but one-half 
 of its chromosomes, as distinct and individual descendants 
 of those parents." 
 
 35. Results of union of egg and sperm. — Extraor- 
 dinary changes follow immediately the physical union 
 of the egg and spermatozoon. These changes are of 
 the most fundamental significance in connection with 
 discussions of development and inheritance. 
 
 36. Changes in the ovum. — The entrance of the 
 sperm seems to exert an influence which permeates the 
 entire constitution of the egg substance. Various and 
 important changes now take place, ending finally in an 
 exact union of the germ substance of the two sex cells, 
 thus forming the new or daughter cell. The daughter 
 cell is the beginning of a new individual and becomes the 
 offspring of the parents, from which the sperm and ovum 
 were derived. When the sperm enters the egg, the 
 vitelline membrane is thrown around the outside of the 
 ovum. The nucleus of the egg, which is now called the 
 germinal vesicle, moves to the wall, and changes occur 
 which result in the formation of the polar bodies. This 
 process prepares the germ nucleus of the egg for ferti- 
 lization. 
 
 The polar bodies are formed by successive divisions 
 
REPRODUCTION 37 
 
 of the egg nucleus. During their formation, the number 
 of chromosomes characteristic of the species is reduced 
 by half, so that when the egg nucleus is finally ready for 
 union with the sperm nucleus, it contains exactly one-half 
 the number of chromosomes usually present in the cell. 
 There are formed in all three polar bodies. The divisions 
 which occur in their formation separate the mass of 
 chromatin originally present in the germinal vesicle 
 into four equal parts. One-fourth part enters the egg 
 nucleus and the other three parts are distributed, one to 
 each of the polar bodies. The polar bodies are in no 
 direct way concerned in fertilization and soon disinte- 
 grate and disappear. 
 
 37. Changes in the spermatozoon. — After contact 
 with the egg, the tail of the sperm soon degenerates 
 either outside or, in some cases, inside the egg. 
 
 The nucleus of the sperm grows rapidly in size. The 
 nucleus is further stimulated to cell division by the 
 influence of the cytoplasm of the egg. 
 
 38. The significance of reduction. — All the phenom- 
 ena attending the processes of fertilization seem to 
 have been specifically arranged for the purpose of bringing 
 about a reduction of the number of chromosomes in the 
 germ-cells to one-half that found in the other cells of the 
 body. A result so universal in plants and animals must 
 possess some significance in the reproduction of living 
 forms. This change is characteristic of the germ-cells 
 only and always occurs prior to and in preparation for 
 the union of the spermatozoon and the egg. What is 
 the real significance of the reduction of the chromosomes ? 
 Is this reduction of the chromatin a quantitative one, or 
 is it in some way a qualitative division? It must be 
 admitted that we cannot yet give positive answers to 
 
38 THE BREEDING OF ANIMALS 
 
 these questions. That this process is one of fundamental 
 significance and is intimately connected with the problem 
 of how characters are transmitted, is certain. Mani- 
 festly its purpose is to provide for a constant number of 
 chromosomes in the body tissues. It is not, as some have 
 maintained, a mere mass reduction of the chromatin. 
 Weismann's ingenious theory of the germ-plasm attempts 
 to explain the process and to point out the hereditary 
 significance of reduction. In an earlier investigation, 
 Roux held that the hereditary qualities are represented 
 by the individual chromatin granules. During cell di- 
 vision, these arranged themselves side by side in the 
 spireme thread, and the splitting of the spireme thread 
 longitudinally actually resulted in halving each indi- 
 vidual chromatin granule. Quoting Wilson,^ — " Roux 
 assumes, as a fundamental postulate, that division of the 
 granules may be either quantitative or qualitative. In 
 the first mode, the group of qualities represented in the 
 mother granule is first doubled and then split into equiva- 
 lent daughter groups, the daughter cells, therefore, receiv- 
 ing the same qualities and remaining of the same nature. 
 In ' qualitative division,' on the other hand, the mother 
 group of qualities is split into dissimilar groups, which, 
 passing into the respective daughter nuclei, lead to a 
 corresponding differentiation in the daughter cells. By 
 qualitative divisions, occurring in a fixed and predeter- 
 mined order, the idioplasm is thus split up during ontogeny 
 into its constituent qualities which are, as it were, sifted 
 apart and distributed to the various nuclei of the embryo. 
 Every cell nucleus, therefore, receives a specific form of 
 chromatin which determines the nature of the cell at a 
 given period in its later history. Every cell is thus 
 
 1 Loc. cit. 
 
REPRODUCTION 39 
 
 endowed with a power of self-determination which Kes 
 in the specific structure of its nucleus, and its course of 
 development is only in a minor degree capable of modi- 
 fication through the relation of the cell to its fellows." 
 
 Weismann conceives that the chromatin (idioplasm) 
 of the germ-cell exists in the form of minute particles 
 which combine to form aggregates, and these again unite 
 to form compound groups and so on until finally we have 
 the chromosomes. He calls the smallest groups deter- 
 minants, the next larger groups ids (chromatin granules), 
 these in turn combining and forming idants or chro- 
 mosomes. Weismann in explanation of his theory says : 
 " Ontogeny depends on a gradual process of disintegra- 
 tion of the id of germ-plasm, which splits into smaller 
 and smaller groups of determinants in the development 
 of each individual. Finally . . . only one kind of 
 determinant remains in each cell, viz. that which has to 
 control that particular cell or group of cells. In this 
 cell it breaks up into its constituent biophores and gives 
 the cell its inherited specific character." 
 
 In developing this theory it is necessary to assume a 
 very stable condition of the germ-plasm. For example, 
 one must assume that some portion of the original germ- 
 plasm is passed on to the germ nucleus unchanged in 
 structure from generation to generation. 
 
 The theories of both Roux and Weismann are in part 
 only based upon demonstrated phenomena occurring in 
 the cell. Some of the most fundamental and far-reaching 
 postulates of these theories are highly speculative and 
 cannot be demonstrated by any known method of re- 
 search. It must be admitted, however, that Weismann's 
 theory of the germ-plasm with some modifications comes 
 nearer to an adequate explanation of the changes which 
 
40 THE BREEDING OF ANIMALS 
 
 can actually be observed in the cell during the fertiliza- 
 tion and maturation of the germ-cells than any other so 
 far advanced. 
 
 39. The origin of the germ-cells. — The origin of the 
 germ-cells and the phenomena attending the process of 
 the reduction of the chromosomes are of great fundamental 
 significance. The functions of the chromatin in modern 
 theories of heredity, the particular meaning of the pro- 
 cesses which result in reducing the number of chromosomes 
 to one-half that found in the body-cells, are problems 
 of the greatest interest in modern biology. 
 
 The maturation of the germ-cells is brought about 
 by similar processes in the egg and sperm. The impor- 
 tant result which is the reduction of the number of chro- 
 mosomes is accomplished in each. This is brought about 
 finally in the last two maturation divisions resulting in four 
 cells, each of which contains but one-half the number of 
 chromosomes characteristic of the same cells. In the 
 female three of the four cells are the polar bodies which 
 are abortive and disappear. The remaining cell is the 
 ovum and becomes the carrier of the hereditary substance 
 of the female. In the male the reduction divisions occur 
 as in the female, but all four cells are functional and may 
 take part in the process of fertilization. 
 
 40. Maturation and reduction in the female (oogenesis) . 
 — The female germ-cells are derived from the primordial 
 germ-cells of the mother. Successive divisions of the 
 primordial germ-cells result in the development of a 
 number of cells known as oogonia. 
 
 From these the ovarian eggs are directly derived. 
 Their growth is characterized by an increase in the size 
 of the nucleus which in the ovarian egg (oocyte) becomes 
 the germinal vesicle. Food materials develop in the 
 
REPRODUCTION 41 
 
 cytoplasm, which is now called the yolk. During all the 
 changes described above, the number of chromosomes 
 in the ova remains the same as in the body-cells. When 
 the Qgg undergoes the final preparation for fertilization, 
 as we have seen, the number of chromosomes is reduced 
 by one-half. 
 
 41. Reduction in the male (spermatogenesis). — The 
 changes which bring about the reduction of the chromatin 
 in the male germ-cell are almost exactly similar to those 
 which have been described in the development of the 
 ovarian egg. The spermatozoa originate in the primor- 
 dial germ-cells. In their earlier development by cell 
 division, numerous spermatogonia are formed which for 
 a time continue to divide with the typical number of 
 chromosomes found in the soma-cells. In time the 
 spermatogonia cease to divide further and become larger. 
 At this stage they are physiologically equivalent in func- 
 tion to the oocyte of the female and are known as sperma- 
 tocytes. There now occur two divisions resulting in four 
 cells, each having but one-half the typical number of 
 chromosomes. Unlike the reducing process in the female 
 which results in only one perfect ovum and, three abortive 
 cells, all four sperm-cells are functionally perfect. 
 
 42. The period of the oestrum or heat. — In all the 
 domestic mammals, the ripening of the first egg is asso- 
 ciated with the first appearance of heat. It is the first 
 evidence of puberty and is accompanied by the rapid 
 development of all the secondary sexual characters dis- 
 tinctive of sex. It is by no means certain that the stimu- 
 lus which causes the heat or oestrum in animals originates 
 in the ovary. It is possible that the stimulus to egg forma- 
 tion is to be found in the influences set in motion by the 
 oestrum itself. The production of ova ^nd the heat 
 
42 THE BREEDING OF ANIMALS 
 
 period are so closely associated that the stimulus, what- 
 ever it may be that causes the one, will probably under 
 normal conditions directly or indirectly cause the other. 
 
 Heape has maintained that since it is known that, 
 in various animals, either menstruation or oestrus may 
 take place without ovulation, and that ovulation may 
 occur without the coincidence of menstruation (Leopold 
 and Mironoff, 1894) or of oestrus (fat), the possibility of 
 isolating these functions is demonstrated. Thus it is 
 no longer impossible to suppose that, while they are 
 both due to similar stimulating influences, one of them 
 may be developed in excess of the other.^ 
 
 It is probable that heat may sometimes occur with- 
 out the production of an egg, and it is possible that the 
 production of an egg may not always be accompanied by 
 heat, but when such a condition exists, it is to be regarded 
 as the exception and not the rule. It is very clear that 
 the oestrum and ovulation are influenced by nutrition. 
 An insufficient supply of food, deficient in the essential 
 elements required for the normal development of animals, 
 retards the first appearance of heat in young animals and 
 causes irregular periods in mature animals. Breeders 
 of live-stock have long known that the oestrum can 
 be materially influenced by the method of feeding. 
 Skillful stockmen feed the females in such a manner 
 as to cause them to be " gaining " at mating time. This 
 is accomplished by richer feeding or turning to fresh 
 grass. 
 
 43. Artificial insemination. — The transfer of the 
 semen of the male to the uterus of the female by the aid 
 of instruments or capsules is known as artificial insemina- 
 tion or, more commonly among practical breeders, as 
 
 ^ Heape, loc. cit., p. 34. 
 
O •- f-i •- 
 
 ... cJ « j5 *s 
 
 > > 73 -S 
 2 t-H o -- • 
 
 .co- 
 
 in 
 
 
 .2 S 
 
 o o S 2 
 
 2 2 °^ 
 
 03:5 >> •- 
 
 CO 
 
 t; g > S 
 
 S -H "^ ^ 
 
 > 03 lO* ** "^ 
 
 ^ i "1= 
 
 (V, '^ O) M > 
 
 3 ?! A 
 
 c3 ^ 
 
 a ^ 
 
 o3 oi 
 
 a 
 
 o C 
 
 j3 » 03 '^ 
 -I o 
 
 03 
 
 o o 
 
 O 
 
 tc -^ 3 
 
 s ? ^ - 
 
 r! ''-' .g <0 
 
 S'V, '^ 
 
 „ Sbco t^T3 
 d 03 „t3 
 
 
 h3 
 
 
REPRODUCTION 43 
 
 artificial impregnation. The artificial insemination of 
 the domestic animals, particularly cows and mares, has 
 been practiced in various parts of the world for many 
 years. As early as the time of Spallanzani ^ (1784) arti- 
 ficial insemination was successfully accomplished in 
 dogs. It seems probable also that the Arabs have been 
 familiar with the possibilities of this practice for centuries.^ 
 The insemination of mares, cows and bitches as a remedy 
 for sterility has been demonstrated by Huish.^ The Rus- 
 sian investigator Iwanoff ^ was successful in inducing 
 pregnancy in rabbits and guinea pigs by artificial jneans. 
 Artificial insemination is employed for the purpose of 
 overcoming certain forms of sterility in mammals, specifi- 
 cally, constriction of the muscles surrounding the neck 
 of the uterus. It is also successful in cases of acid secre- 
 tions of the vagina which are unfavorable to the proper 
 functioning of the sperm-cells after they have been de- 
 posited in the generative organs of the female. Artificial 
 insemination is also a practical method of extending the 
 usefulness of a valuable male, as by this means one male 
 may be used successfully for breeding a much larger 
 number of females. 
 
 44. Methods of artificial insemination. — The most 
 common methods in use are insemination with a specially 
 made syringe or the introduction of the semen in capsules. 
 By one method the semen is collected from the vagina 
 of the mare after the service of the stallion by introducing 
 the syringe into the vagina until the mouth of the syringe 
 
 1 Spallanzani, "Dissertations," vol. II, 1784. 
 
 2 Gautier, "Le Fecondation Artificielle," Paris, 1889. 
 
 3 Huish, "The Cause and Remedy of Sterility in Mares, 
 Cows and Bitches," London, 4th edition, 1899. 
 
 ^ Iwanoff, "De la Fecondation Artificielle chez les Mammi- 
 feres," Arch, des Sciences Biologiques, vol. XII, 1907. 
 
44 THE BREEDING OF ANIMALS 
 
 is immediately over the cup-shaped depression just in 
 front of the cervix. The semen is then drawn into the 
 syringe and the instrument introduced into the vagina 
 of the mare to be artificially bred and pushed carefully 
 through the neck of the womb to insure the depositing 
 of the semen inside the uterus. Care should be taken 
 not to introduce the point of the syringe into the opening 
 to the bladder which is only five or six inches from the 
 external opening of the vagina. The transfer of the 
 semen to the waiting mare should be made without un- 
 necessary delay and all instruments should be kept at 
 body temperature during the operation. All instruments 
 should be thoroughly sterilized in hot water before using. 
 
 Many interesting questions of biological and practical 
 interest are raised by the practice of artificial insemina- 
 tion. How long after the semen is collected will it con- 
 tinue to be potent? What external conditions such as 
 cold, heat, light and air affect the vitality of the germ? 
 How long does the semen retain its vitality within the 
 reproductive organs of the female? Partial answers 
 to these questions have been given through the investi- 
 gations of Lewis.^ 
 
 45. Conditions influencing the vitality of the sperm- 
 cells. — The vitality of semen collected and preserved 
 at different temperatures under laboratory conditions 
 showed great variations. High temperatures were gen- 
 erally unfavorable. At the end of one hour the percentage 
 of semen which was alive and active was : at 33° C, 40 
 per cent ; at 30° C, 45 per cent ; at 26° C, 85 per cent, and 
 at 18° C, 90 per cent. At the end of two-and-one-half 
 hours all the sperm-cells maintained at the temperatures 
 of 33° C. and 39° C. were dead, while 65 per cent of the 
 
 1 Lewis, Oklahoma Experiment Station, Bulletins 93 and 96. 
 
REPRODUCTION 45 
 
 cells were alive at the temperature of 18° C, and 45 per cent 
 of the cells kept at a constant temperature of 26° were 
 still active. The sperm-cells from boars of several breeds 
 showed similar behavior and in every case the higher 
 temperatures were unfavorable. Semen kept at a tem- 
 perature of 31 to 32° C. and exposed to the diffused light 
 of the laboratory resulted in the death of practically all 
 the sperm-cells at the end of seven hours. A portion of 
 the same semen protected from the light by wrapping 
 in black paper showed 40 per cent of the germ-cells alive 
 at the end of the same time. The spermatozoa exposed 
 to direct sunlight for ninety minutes were all killed, while 
 the portion protected from direct rays of the sun showed 
 80 to 90 per cent alive at the end of the same time. 
 
 46. Effect of too frequent breeding on the sperm-cells. 
 — Lewis ^ found that the number of sperm-cells in the 
 semen collected from the first service of a vigorous stal- 
 lion was 428,000 to a cubic millimeter. The stallion 
 was permitted one service daily for nine days. The 
 number of sperm-cells diminished rapidly until there 
 were only 74,300 sperm-cells to a cubic millimeter at 
 the ninth service. The continuous and frequent service 
 of the stallion also resulted in weakening the vitality of 
 the sperm-cells. The semen from the first service kept 
 at constant temperature of 13 to 21° C. showed twenty- 
 five per cent of the sperm-cells alive after six-and-one-half 
 hours. The sperm-cells in semen collected from the 
 ninth service showed only five per cent of the cells alive 
 after six hours. Simple exposure to the air seemed to 
 have no deleterious effect on the vitality of the sperma- 
 tozoa. 
 
 The standard of judging of the vitality of the sperm- 
 
 1 Loc. cit., p. 35. 
 
46 THE BREEDING OF ANIMALS 
 
 cells in this investigation was microscopic evidence of 
 normal motion and as pointed out by Lewis this method 
 does not necessarily measure the' ability of the sperm 
 successfully to fertilize the ovum. The addition of water 
 to semen seems to lower the vitality of the sperm-cells. 
 The presence of urine also has a retarding influence on 
 the activity of the spermatozoa. Sperm-cells kept in 
 contact with rubber lose their vitality more quickly than 
 when preserved in a glass retainer. 
 
 47. Vitality of spermatozoa within the female genera- 
 tive organs. — How long do the sperm-cells retain their 
 vitality after being deposited in the generative organs 
 of the female ? The answer to this question is of practical 
 importance, as it has an important bearing upon the 
 particular time or stage during the heat at which the 
 union of the male and female will be most likely to result 
 in offspring. 
 
 The period during which perfectly healthy sperm-cells 
 retain their vitality and power of motion under labora- 
 tory conditions is comparatively short. And while 
 the conditions for a longer period of vitality are pre- 
 sumably much more favorable inside the generative 
 system of the female, yet investigations on mares and 
 sows ^ seem to point to the fact that the life of the sperm- 
 cells in the uterus of the female is comparatively brief. 
 This is contrary to the opinion of many practical breed- 
 ers. It is generally believed that the spermatozoa retain 
 their vitality in the reproductive organs of the female 
 for a number of days. It is stated by some veterinary 
 authorities ^ that the spermatozoa will live in the vagina 
 or womb of the mare from six to twelve days under the 
 
 1 Lewis, Oklahoma Experiment Station, Bulletin 96. 
 
 2 Breeder's Gazette, vol. 43, 1903, p. 683. 
 
REPRODUCTION 47 
 
 most favorable conditions. A normal alkaline solution 
 in the uterus is the most favorable medium for the long 
 continued vitality of the sperm-cells. It is very often 
 the case that the secretions in the reproductive organs 
 of the mare are acid and such a chemical condition is very 
 unfavorable to the continuance of the life of the sperm. 
 It is true that the sperm-cells will live but a few hours 
 in such an acid medium as is sometimes found in the 
 uterus. A study of the literature on the longevity of 
 the sperm-cells in the female reproductive organs is 
 somewhat confusing. It is probable that very consider- 
 able differences exist in the vitality of the spermatozoa 
 from different individuals, but even this is scarcely suffi- 
 cient to explain the wide discrepancies reported by vari- 
 ous investigators. Various authors ^ have reported the 
 presence of live and motile spermatozoa in the uterus of 
 dogs eight days after coition. Marshall and Jolly ^ found 
 live sperm-cells in the vasa deferentia of the rabbit ten 
 days after the removal of the testes, but all were dead at 
 thirteen days. The sperm-cells of bats are reported by 
 Benecke and others to be deposited in the female organs 
 in the autumn, there to remain dormant until the follow- 
 ing spring. Ovulation is induced by the warm weather 
 of early spring and the spermatozoa which have lain 
 dormant throughout the hibernating period become active 
 and insemination occurs. In the domestic hen, accord- 
 ing to Lillie,^ '^ The period of life of the spermatozoa 
 within the oviduct is considerable as proved by the fact 
 that hens may continue to lay fertile eggs for a period of 
 
 1 Hertwig, "Handbuch der Entwicklungslehre." 
 
 2 Marshall and Jolly, " The (Estrus Cycle in the Dog." Phil. 
 Transactions. B., vol. 198, 1905. 
 
 3 Lillie, "The Development of the Chick," 1908, p. 35. 
 
48 THE BREEDING OF ANIMALS 
 
 at least three weeks after isolation from the cock. After 
 the end of the third week the vitality of the spermatozoa is 
 apparently reduced, as eggs laid during the fourth and fifth 
 weeks may exhibit at the most abnormal cleavage, which 
 soon ceases. Eggs laid forty days after isolation are cer- 
 tainly unfertilized and do not develop."^ That the sperma- 
 tozoa may continue to fertilize eggs in the hen for at least 
 twenty days after coition is noted also by Spallanzani. 
 
 The researches of Lewis ^ including records of twenty- 
 five sows showed that in three cases only were the sperm- 
 cells alive and active after twenty hours existence in the 
 female organs of generation. In two cases live sperma- 
 tozoa were collected from the uterus at the end of forty 
 hours. In most cases the sperm-cells taken from the 
 female organs were all dead at the end of sixteen hours 
 after the sow had been bred to a healthy normal boar. 
 The rupture of the Graafian follicles was found to occur 
 almost universally during the last part of the heat. *' In 
 no case were the follicles found ruptured during the first 
 twenty-four hours of heat and in most of the cases a 
 period of thirty hours elapsed after the first signs of heat 
 before many of the egg-cells escaped from the ovary." 
 In no case were the Graafian follicles found ruptured in 
 sows which were examined early in the heat. In one sow 
 ovulation did not occur until forty-five hours and in 
 another case seventy hours after the beginning of heat. 
 From the fact that in swine the duration of the vitality 
 of the sperm-cells in the generative organs is so short and 
 that ovulation occurs during the last part of the heat, it 
 is apparent that sows should be bred during the last 
 part of the heat. To be more explicit, the sow should 
 
 1 Spallanzani, "Dissertations," vol. II, 1784. 
 
 2 Loc. cit., p. 7 et seq. 
 
REPRODUCTION 49 
 
 be bred not less than thirty hours after the beginning 
 of heat. In practice, the animal-breeder may safely 
 assume that the normal active existence of the sperm- 
 cells in the uterus of mammalian animals is short and 
 that therefore to insure successful conception, the actual 
 service of the male should occur very near to the time 
 when the heat is at its height. 
 
 48. Effect of intoxication of the male parent on his 
 offspring. — The fertilized egg may be so influenced by 
 various environmental factors that the embryos arising 
 from such eggs are affected in a definite way. Similar 
 effects from factors calculated to influence the sperm- 
 cells are much more obscure. It is very difficult from 
 the very nature of the factors involved to influence the 
 sperm-cell in such a definite way that the influence will 
 directly modify the offspring. Observations on this 
 point have been numerous but few experiments under 
 proper control have been made. In all experiments 
 conducted for the purpose of influencing the male germ- 
 cells, it is necessary to work through the animal body. 
 Under these circumstances it is not always easy to deter- 
 mine with certainty whether the modifications resulting 
 from various treatments are the direct result of the treat- 
 ment on the sperm-cell or the secondary effects from the 
 changes in the parental body itself. Among humans 
 it is generally recognized that indulgence in alcoholic 
 drinks by the male results in various defects in the off- 
 spring. In one observation Lippich studied ninety-seven 
 children conceived during intoxication. Of this number 
 all were defective except fourteen.^ Among seven births 
 
 ^Stockard, "Effect of Intoxicating the Male Parent," Amer- 
 ican Naturalist, vol. 47, p. 641 ; also Journal of Heredity, vol. 
 5, Feb. 1914. 
 
 E 
 
50 THE BREEDING OF ANIMALS 
 
 from conceptions during drunkenness, Sullivan reports 
 six as having died of convulsions and the seventh was still- 
 born. Chronic alcoholism has been found to change the 
 structure of the testicular glands. The children of lead 
 workers are known to be sometimes defective. 
 
 Stockard ^ has made some very interesting experiments 
 which clearly show that the sperm may be so affected 
 that the resulting offspring will be defective. As a result 
 of mating normal female guinea pigs with males which 
 were in a state of intoxication from inhaling alcohol fumes, 
 many of the offspring were defective. *' Out of G9 full 
 term young, of which 54 were born alive, only 33 have 
 survived and many of these are small and excitable 
 animals, and although not treated themselves have since 
 given rise to defective offspring in several cases where 
 they have been mated with another." 
 
 If these results are confirmed, we must conclude that 
 it is possible to modify the offspring by special treatment 
 of the paternal parent. Some evidence is submitted 
 by this investigation to show that the bad effects are not 
 limited to the immediate offspring but are transmitted 
 to subsequent generations. 
 
 49. Effect of lead poisoning on the male germ-cells 
 as indicated by the offspring. — That the children of 
 fathers who work in lead-manufacturing industries are 
 often defective has been observed for a long time. Cole ^ 
 and Bachhuber have reported results of feeding lead 
 acetate to rabbits and fowls. The treatments were 
 given to male parents alone and these were mated with 
 normal females. Injury to the offspring from such treat- 
 
 ^ Loc. cit. 
 
 2 Cole and Bachhuber, "Proceedings of the Society for 
 Experimental Biology and Medicine," 1914, XII, pp. 24-29. 
 
REPRODUCTION 51 
 
 ments was frequent. The offspring of male rabbits 
 treated with lead acetate were smaller and had distinctly 
 lower vitality than the offspring of normal parents under 
 similar conditions. The results from lead-poisoning of 
 male fowls indicated that their offspring is of distinctly 
 lower vitality than of offspring from normally healthy 
 fowls. 
 
 The importance of these investigations to the practi- 
 cal breeder lies not in the fact that alcohol and other 
 poisons may modify the male germ-cell and subsequently 
 the offspring, but that the sperm-cell is capable of such 
 reactions to environmental conditions that the progeny 
 are profoundly changed or their development entirely 
 prevented. If the offspring may be so modified through 
 the sperm-cell by alcohol and lead acetate, then it is in all 
 probability susceptible to other influences. It is a well- 
 known fact that many conditions in ordinary breeding 
 practice do modify the birth rate and the characters of 
 the offspring. Certain feeds are known to have a more 
 or less definite relation to the breeding powers. Investi- 
 gations under proper control planned to test the influence 
 of special feeds on the sperm-cell are lacking. At vari- 
 ous times breeders have reported that alfalfa, clover, sugar 
 and other materials when fed to breeding females have 
 resulted in difficult conception or in weak offspring. 
 Whether these feeding stuffs have an injurious effect on 
 the male germ-cell is not known and cannot easily be 
 determined in ordinary farm practice. 
 
CHAPTER III 
 THE BREEDING SEASON 
 
 The arrival of puberty or the breeding age in the 
 domestic animals does not mean that the breeding func- 
 tion is exercised . continuously thereafter. In the case 
 of all animals, domestic and wild, there exists a certain 
 periodicity in the process of reproduction. The iphys- 
 iological activities which result in the propagation of 
 young recur with a certain rhythm, and under normal 
 conditions there is a definite period between the 
 birth of young and the reappearance of reproductive 
 activities. 
 
 This rhythm may be disturbed by certain external 
 conditions, although in the higher animals it recurs with 
 considerable regularity. The reproductive functions are 
 one of the first to be affected by a marked change in the 
 environment. Breeders have long recognized this fact. 
 It has been observed that a stallion or bull imported 
 from Europe to America often fails to breed well the 
 first year. The same condition has been found to exist 
 in the case of mares and cows. 
 
 50. Changed conditions. — Darwin has described how 
 changes in the ordinary habits of animals may profoundly 
 influence their reproductive functions. Animals in cap- 
 tivity rarely breed. Elephants, tigers, lions and many 
 other species when confined fail to breed at all or breed 
 
 52 
 
THE BREEDING SEASON 53 
 
 with great irregularity. Failure to breed under these 
 conditions is not the result of a diseased condition of the 
 generative organs ; as Marshall has said, " It would seem 
 probable that failure to breed among animals in a strange 
 environment is due not, as has been suggested, to any 
 toxic influence on the organs of generation, but to the 
 same causes as those which restrict breeding in a state 
 of nature to certain particular seasons, in that the sexual 
 instinct can only be called into play in response to definite 
 stimuli, the existence of which depends to a large extent 
 upon appropriate seasonal and climatic changes." ^ 
 
 Among the domestic animals, the generative functions 
 are more active in the spring season. This is true of 
 the horse, the cow and the pig. Sheep breed more readily 
 in the autumn. 
 
 How much the increased sexual activity of the domestic 
 animals may be due to climate and how much to the 
 change in the food supply, it is not easy to determine. 
 Food itself as distinct from climate has a direct influence 
 on the breeding powers of animals. The green succulent 
 grass upon which the animals feed in the spring may be 
 the efficient cause of increased sexual activity at that 
 season. The ewes that exhibit an increased tendency to 
 reproduction in the autumn may be stimulated in a similar 
 manner by the general abundance of fresh feed which is 
 characteristic of that season. It has long been the cus- 
 tom among skillful shepherds to provide fresh, succulent 
 feed in abundance to ewes at the time of turning in the 
 rams. This practice is called " flushing." The shepherds 
 claim that this practice causes the ewes to come in heat 
 more promptly and with greater regularity. It is also 
 claimed that a larger number of lambs will be produced 
 
 ^ Marshall, "The Physiology of Reproduction," p. 5. 
 
54 THE BREEDING OF ANIMALS 
 
 at lambing time as a result of this practice. It is undoubt- 
 edly true that the practice stimulates sexual activity 
 and does cause the ewes to come in heat with greater 
 regularity. It is probable that this result is due both 
 to the character of the feed and its abundance. 
 
 The breeding season may be influenced by heredity. 
 Certain breeds of sheep will breed readily at all seasons. 
 The Dorset Horned breed comes in heat and breeds at 
 all seasons, while most of the mutton and merino sheep 
 breed readily only in the fall. Other conditions which 
 are known to influence the breeding season in domestic 
 animals are the kind of food, condition of the animal, 
 age and breed. 
 
 Evvard ^ has shown that sows gaining in weight when 
 bred produced larger litters than sows that were fed only 
 a maintenance ration. 
 
 51. Phases of the breeding season. — The breeding 
 season is divided into more or less distinct phases and 
 these have been described and named by Heape ^ and 
 Marshall as the prooestrum, oestrum, metoestrum and 
 dioestrum. 
 
 52. Prooestrum. — The first part of the sexual season 
 is occupied by the prooestrum. This period is character- 
 ized by marked changes in the generative organs, the 
 uterus becoming congested, while in the later stages 
 there is often a flow of blood from the external opening 
 of the vagina. The prooestrum is the period often re- 
 ferred to by breeders as the time when an animal is '' com- 
 ing in heat " or coming in season.^ 
 
 1 Evvard, in "Report of American Breeders' Association," 
 191. 
 
 ^ Heape, Quarterly Journal of Microscopical Science, vol. 44, 
 p. 1. 
 
 ^ Marshall, "The Physiology of Reproduction," p. 36. 
 
THE BREEDING SEASON 55 
 
 53. (Estrum. — The oestrum may be referred to as 
 the heat proper and represents the time when the female 
 will receive the male. It is during this period that the 
 peculiar symptoms well known to practical breeders are 
 exhibited. This phase is characterized by unusual 
 activity on the part of the animal. Great restlessness, 
 constant movement and often great mental excitement 
 are observed in animals which are in heat. The genital 
 organs become congested. The mammary glands in 
 animals not suckling young increase in size. The external 
 genitals, particularly the vulva, become swollen and red 
 and mucous and bloody excretions flow from the genera- 
 tive organs. In many animals, there are frequent at- 
 tempts at urination. The female sometimes utters loud 
 cries or grunts, as in the sow. Cows, ewes and sows 
 lose appetite, and get " off feed," often losing in weight. 
 In all meat-producing animals, when the females are 
 fattened for the markets, this is an economic loss to the 
 feeder. In some sections, the larger feeders have spayed 
 the heifers intended for fattening and thus prevented 
 this loss. If the animal is bred and conception occurs, 
 these periods of excitement are prevented, but pregnant 
 fat animals are less valuable on the market and are always 
 discriminated against by the buyer. 
 
 54. Metoestrum. — The oestrum is followed by a 
 gradual subsidence of the symptoms which characterize 
 this period, provided coition does not take place and 
 pregnancy result. In the latter case, oestrum is followed 
 by gestation. If the female is not bred to the male during 
 oestrum, the sexual excitement of the period gradually 
 passes away and the animal returns to a normal condition. 
 
 55. Dioestrum. — The dioestrum represents the time 
 of rest for the generative system between the periods of 
 
56 THE BREEDING OF ANIMALS 
 
 sexual activity. This varies greatly in different animals. 
 Again quoting Marshall, " In some animals, such as the 
 dog, the metoestrous period is followed by a prolonged 
 period of rest or anoestrum. In others, such as the rat 
 or the rabbit, the metcestrum may be succeeded by only 
 a short interval of quiescence. This short interval, 
 which sometimes lasts for only a few days, is called the 
 dioestrum. This in turn is followed by another prooes- 
 trous period, and so the cycle is repeated until the sexual 
 season is over. Such a cycle (consisting of a succession 
 of the four periods, prooestrum, oestrum, metcestrum, and 
 dioestrum) is known as the dicestrous cycle. The num- 
 ber of dicestrous cycles in one sexual season depends 
 upon the occurrence or nonoccurrence of successful 
 coition during oestrus. Thus, if conception takes place 
 during the first oestrous period of the season, there can 
 be no repetition of the cycle, at any rate until after parturi- 
 tion. The cycle may then be repeated. If conception 
 does not occur at any oestrus during the sexual season, 
 the final metoestrous period is succeeded by a prolonged 
 anoestrous or non-breeding period. This is eventually fol- 
 lowed by another prooestrum, marking the commencement 
 of a new sexual season. The complete cycle of events 
 is called the oestrous cycle." ^ 
 
 56. Puberty. — The reproductive functions are not ac- 
 tive in the young mammal during its very early existence. 
 The nutritive system during the same period is char- 
 acterized by unusual functional activity and a high degree 
 of efficiency. The food consumed during the early exist- 
 ence of the mammal produces larger gains in live weight 
 than the same food at any later period of its life. 
 
 The growth processes continue to function with great 
 
 1 Marshall, "The Physiology of Reproduction," p. 37. 
 
THE BREEDING SEASON 57 
 
 activity for a certain period and the reproductive organs 
 gradually develop until at a certain age, or stage of devel- 
 opment, the essential organs are matured and begin 
 to develop perfect germ-cells. The stage of develop- 
 ment when the ovaries of the female produce perfect 
 eggs is called the period of puberty and represents the 
 beginning of the breeding season. The arrival of puberty 
 in the female is accompanied by the ripening of the first 
 ovum or egg and the appearance of the oestrum or heat. 
 The beginning of puberty in the female is marked by 
 certain characteristic changes. The mammary glands 
 increase in size, the general activities of the body are 
 accelerated and the animal performs certain actions that 
 are peculiar to the period of the oestrum or heat. The 
 coming of puberty in the male is likewise associated with 
 certain bodily changes which are well recognized by the 
 practical breeder. In the stallion, the neck, and partic- 
 ularly the crest develops, and the forequarters generally 
 are relatively better developed than the hindquarters. 
 The most significant changes however, are physiological. 
 The entire system assumes a state of greater activity. 
 Not only the generative system is concerned in this change 
 but all organs and functions of the body become more 
 active. In the bull, the external and visible changes 
 are an enlarging and thickening of the horns, and thicken- 
 ing and enlarging of the neck and crest. The increased 
 activity of males is indicated by greater restlessness, 
 irritability and the development of a pugnacious tendency. 
 Bulls and stallions often become vicious and unmanage- 
 able and engage in deadly struggles for supremacy. 
 These contests are also common among the males of wild 
 animals. Such battles have been observed as common 
 among stags and wild stallions. 
 
58 THE BREEDING OF ANIMALS 
 
 57. Conditions influencing puberty. — The age at 
 which puberty begins in the various breeds of the domestic 
 animals is dependent upon the kind of animal, the 
 breed, the food and general care of the young before 
 puberty. Puberty in the mare comes between the ages 
 of twelve and eighteen months. Under normal condi- 
 tions, the stallion reaches the same stage at twelve or 
 fifteen months. The cow and bull of the modern breeds 
 of cattle under favorable conditions will reach this period 
 at four to six months of age, but under ordinary condi- 
 tions, not until they have attained the age of eight to 
 twelve months. The ewe and ram of the mutton breeds 
 will often arrive at the period of puberty at the age of 
 five or six months, but generally will require longer. 
 The sow and boar will reach puberty sometimes as early 
 as three months of age, but generally at five to six months. 
 The domestic hen has been known to lay eggs at the 
 age of four-and-one-half months. 
 
 The beginning of puberty is greatly influenced by the 
 nutrition of the young animal. This influence begins 
 with the foetus in utero. If the pregnant mother receives 
 a generous supply of nutritious food during the period 
 of gestation, the young will be better developed at birth. 
 The reproductive system along with the other organs will 
 have developed somewhat nearer to the stage of sexual 
 completeness. If such generous nutrition is continued 
 after birth, the young animal will reach the period of pu- 
 berty at an earlier period than when fed on a poorer ration. 
 At the Missouri Experiment Station, Eckles ^ has shown 
 in an investigation comparing generous feeding with a 
 lighter ration that the well-fed heifer on the average comes 
 in heat 92 days earlier than those fed less generously. 
 
 1 Eckles, "Dairy Cattle and Milk Production," p. 209. 
 
THE BREEDING SEASON 59 
 
 68. The oestrum and lactation. — In many of the 
 domestic mammals, the period of heat is influenced by 
 lactation. Nursing the young may prevent entirely or 
 retard the appearance of heat after parturition. Ewes 
 seldom come in heat while suckling young. In the case 
 of cows, the oestrum is retarded. There is much varia- 
 tion in the length of the time elapsing between the birth 
 of the young and the first appearance of heat in the cow. 
 It is probably about sixty days, although it may recur 
 earlier or later than this period. The sow will generally 
 come in heat three days after giving birth to a litter of 
 pigs, but the oestrus period does not again occur until 
 after the pigs are weaned. A prominent breeder of Duroc 
 Jersey hogs, S. Y. Thornton, says, " In many cases, a 
 sow that is in good condition will come in heat the third 
 day after farrowing. I have bred them at that time but 
 seldom knew one to get with pig if she was suckling, but 
 one that has lost her pigs will invariably get with pig 
 from the first period which is usually the third day after 
 farrowing. A sow will often come in heat when her 
 pigs are four to six weeks old if she has been well fed." 
 The distinguished breeder of Berkshires, A. J. Lovejoy, 
 says, " Sows often show signs of heat on the third day 
 after farrowing, and again at eight weeks after farrowing, 
 while suckling. We find that after weaning a litter, 
 a sow will usually ' come in ' in three to five days." 
 
 The heat period in the mare is very irregular. The 
 " foal heat " occurs in seven to nine days after foaling. 
 The oestrum recurs in most mares throughout the nursing 
 period. But some mares do not come in heat during the 
 time they are suckling foals. It is a well-known fact 
 that there is a strong tendency in some mares to breed 
 only once in two years. In some of the smaller mammals, 
 
60 THE BREEDING OF ANIMALS 
 
 pregnancy is common while the mothers are still suckling. 
 This is true of the domestic rabbit, guinea pig and rat.^ 
 ' 59. Heat during pregnancy. — Animals do not nor- 
 mally come in heat during pregnancy. The fertilization 
 of the egg of the female by the sperm-cell of the male 
 sets in motion a series of physiological phenomena which 
 react upon the ovaries in such a way as to cause a cessa- 
 tion of the heat periods. The ripening of eggs also does 
 not normally occur during pregnancy. There are excep- 
 tions to this rule among certain mammals which seem to 
 be otherwise entirely normal. 
 
 60. Super foetation. — It sometimes happens that a 
 pregnant mammal will not only come in heat and exhibit 
 the various phases of the oestrum, but will ripen an egg 
 and if bred to the male will conceive. Such an occurrence 
 is given the name of superfoetation. This condition is 
 somewhat rare, but has been observed more frequently 
 among mares than other domestic animals. The reason 
 for this is probably due to the fact that the records of 
 breeding are more carefully kept for mares than for cows, 
 sows or ewes. It is difficult even among mares to deter- 
 mine, when twins are born, whether these are the result 
 of one mating or whether they may actually be of different 
 ages. Such authentic cases as are known have been 
 those observed in the mule-breeding districts of the United 
 States. If the mare is first bred to a stallion and three 
 or six weeks later to a jack, and twins are born, one a 
 mule and the other a horse, there can be no doubt that 
 these colts are of different ages. Such a result could 
 only happen in mares which come in heat and ripen an 
 egg during pregnancy. 
 
 ^ Heape, Quarterly Journal of Microscopic Science, vol. 44, 
 p. 43. 
 
THE BREEDING SEASON 
 
 61 
 
 61. Examples of superf oetation. — The literature of 
 animal-breeding is singularly lacking in records of au- 
 thentic cases of superf oetation. The writer has through 
 many years collected evidence of such cases in the mule- 
 breeding districts of Missouri, and a few of these are 
 recorded here : 
 
 '' W. E. Carmichael of Shelby ville, Missouri, bred a 
 mare to a stallion and thirty days later to a jack. At 
 
 Fig. 11. — Normal and usual anterior presentation in mare. 
 
 the end of the normal period of gestation the mare gave 
 birth to twins, one a mule and the other a horse colt. 
 They were both dead at birth." ^ 
 
 A nine-year-old mare belonging to Eugene Rhodes of 
 Fairfax, Missouri, was bred to a stallion in May. In' 
 August she showed unmistakable signs of heat and was 
 mated with a jack. In the month of January following 
 she gave birth to a perfectly formed mule colt and a 
 
 1 Mumford, "Amer. Cyclopedia of Agriculture,' 
 p. 31. 
 
 vol. Ill, 
 
62 THE BREEDING OF ANIMALS 
 
 horse colt, the latter being considerably shriveled in 
 appearance. 
 
 A case is reported by F. K. McGinnis of a Texas bred 
 mare belonging to Mr. Carmack. This mare was bred 
 several times to a stallion during a period of six weeks. 
 She continued to come in heat and the owner, conclud- 
 ing that she was sterile with the stallion, bred her to 
 a jack. She was mated with the jack a number of 
 times during a period of two weeks. Her owner, finally 
 despairing of ever getting the animal in foal, turned her 
 out. At the end of eleven months from the time the 
 mare was first bred to the stallion she dropped twin 
 colts, one a horse and the other a mule. Both were 
 dead at birth. 
 
 An interesting example of superfoetation is recorded 
 by J. F. White of Whitesville, Missouri, who bred a four- 
 year-old mare to a saddle stallion on April 25, 1909. 
 She came in heat again and was bred to a jack May 29, 
 1909. She was again in heat June 12, 1909, and was bred 
 at this period to the saddle stallion first mentioned. On 
 May 11, 1910, the mare gave birth to perfectly formed 
 twin colts. One of these was a mule and the other a 
 horse colt. The mule died from illness at the age of three 
 weeks. The mule colt was a male. The horse colt was 
 a mare and developed into a perfect colt. These were 
 the mare's first colts. 
 
 A draft mare belonging to J. C. Spies of Newark, 
 • Missouri, was bred to a jack. Later she was turned in a 
 lot with her own two-year-old stud colt. The following 
 spring she foaled a mule and a horse colt. The mule 
 died at five days old. The horse colt lived and made a 
 good horse. 
 
 Cases of superfoetation where the same animal is the 
 
THE BREEDING SEASON 63 
 
 sire of both twins are probably much more common than 
 is generally believed. In such cases it is difficult to deter- 
 mine whether the twins foaled at the same time are the 
 result of the fertilization of two eggs ripened at one and 
 the same heat period, or whether the eggs have been ripened 
 at different periods some distance apart. 
 
 A case of this kind has been reported by J. A. Finley 
 of Troy, Missouri. In this case the mare was bred to a 
 jack, and twenty-one days later she was found in heat 
 again and was again bred to the same jack. At the end 
 of a few months she aborted, losing twin mule colts. 
 One of these was much better developed than the other. 
 It seemed clear that the two colts were from different 
 periods of heat, — in this instance, twenty-one days 
 apart.^ 
 
 The following examples are probably to be regarded 
 as cases of superfoetation : — A sow belonging to O. 
 Young of Hopkins, Missouri, gave birth to three pigs. 
 The mother nursed them for four or five days, when she 
 weaned them. Three weeks later the sow gave birth to 
 eight pigs, six of which lived and became thrifty young 
 hogs. 
 
 A young ewe owned by A. Cassity of Linneus, Missouri, 
 gave birth to twin lambs on February 13th. About 
 six weeks later on March 30th, she gave birth to a third 
 lamb. See Plate I. 
 
 62. Recurrence and duration of the oestrum. — The 
 occurrence and duration of heat are influenced by age, 
 species, food supply, season, heredity and other conditions. 
 The heat period persists in the domestic animals for one 
 to fifteen days.^ The duration of the heat period is 
 
 1 From letter to Geo. F. Nardin, dated June 24, 1912. 
 
 2 Hill, "Bovine Medicine and Surgery." 
 
64 THE BREEDING OF ANIMALS 
 
 shortest in the cow and sheep, being in these species 
 usually from twelve to twenty-four hours.^ Mares come 
 in heat seven or nine days after foaling. Bred at this 
 time the mare is more certain to conceive. Dimon,^ 
 an experienced horseman, says that there is no regular 
 period for the return of heat in mares. If mares are well 
 fed they may come in heat at any season, but are more 
 generally in heat in the spring and fall.^ If the mare 
 fails to become pregnant when bred on the ninth day 
 after foaling, she will usually be in heat twenty-one days 
 thereafter. Heat persists for five days and recurs every 
 twenty-one days.^ Heat recurs in the cow three or four 
 weeks after parturition and recurs every twenty-one days. 
 The heat period recurs in sheep from seventeen to twenty- 
 five days. 
 
 In the sow the heat period will be observed three 
 days after delivery and usually not again until the 
 pigs are weaned. Heat again recurs three or four days 
 after weaning the pigs and every twenty-one days there- 
 after. 
 
 63. Effect of ration on recurrence of oestrum. — The 
 recurrence of the oestrum after delivery of the young is 
 often influenced by the character of the ration. At the 
 Wisconsin ^ Experiment Station, Hart, McCollum, Steen- 
 bock and Humphrey found that pregnant cows fed on an 
 exclusive corn ration came in heat in four to six weeks 
 after the first calf. When the cows were fed a ration 
 
 1 Weber, " Untersuchung iiber die Brunst des Rindes," Arch, 
 f. Wissensch. u. Prakt. Tierheilk., 37 Bd., 1911. 
 
 2 Dimon, "American Horses and Horse Breeding." 
 
 3 Reynolds, "The Breeding and Management of Draught 
 Horses." 
 
 ^Curtis, "Cattle, Horses, Sheep and Swine." 
 ^ Wisconsin Exp. Station, Bui. No. 17. 
 
THE BREEDING SEASON 65 
 
 made up exclusively of wheat and its products, the first 
 appearance of heat was from ten to eighteen weeks after 
 calving. Fresh pasture also will often cause animals to 
 come in heat earlier after delivery, and the oestrum will 
 recur with greater regularity. 
 
CHAPTER IV 
 
 GESTATION AND LACTATION 
 
 From the time the egg is fertihzed until the young 
 animal is able to live an independent life covers a period 
 which is of the greatest importance to the growth and 
 development of the individual and the mother. During 
 this time all the physiological activities which are con- 
 cerned with growth are at maximum efficiency; at no 
 other period in the life of the animal is growth so rapid. 
 Not only is the rate of growth very rapid, but the food is 
 utilized much more economically. The stage of develop- 
 ment which takes place in the uterus of the mother is 
 the period of gestation. The period of lactation is the 
 time during which the mammalian animal elaborates 
 milk. 
 
 GESTATION 
 
 64. Indications of pregnancy. — If the animal comes 
 normally in heat and is bred to the male during the heat 
 period, conception occurs in the natural course of events 
 and pregnancy begins as a result of successful conception. 
 Significant physiological changes occur which are recog- 
 nized by the breeder as evidences of pregnancy. Preg- 
 nant animals do not normally come in heat. The chief 
 evidence, therefore, that an animal is ''in foal," "in calf," 
 " in pig," or " in lamb " is the cessation of the periodic 
 appearance of the symptoms accompanying the period of 
 the oestrum. If after breeding the mare does not come in 
 
 66 
 
GESTATION AND LACTATION 67 
 
 heat for thirty daj^s, she is probably safe in foal. The heat 
 period in the mare persists for several days, and therefore a 
 reappearance of evidences of heat shortly after breeding 
 should not be regarded as significant. It is pointed out 
 elsewhere that mares may sometimes come in heat and 
 conceive again (see superfoetation), even though already 
 pregnant. It is also true that some mares will persistently 
 refuse the horse, even though not pregnant. In the cow 
 a period of sexual quiescence for three weeks following her 
 breeding with the bull is good evidence that she is safely 
 " settled " and in due time will give birth to offspring. 
 
 The beginning of pregnancy in an animal is often 
 accompanied by a marked change of temperament. A 
 nervous, excitable mare may become more gentle and 
 docile. It is also true that some mares which when 
 not pregnant are quiet and gentle with other horses 
 become cross during pregnancy and evince a desire to 
 fight other horses. This tendency increases as preg- 
 nancy advances. Following conception the pregnant 
 animal shows a tendency to lay on fat much more rapidly. 
 Feeders sometimes take advantage of this tendency to 
 finish heifers and sows rapidly for the market, but such 
 a practice is to be condemned, as the meat from pregnant 
 animals is less desirable for human food. As pregnancy 
 advances, the abdomen becomes larger at the sides and 
 below and the flank falls in. The loins become depressed, 
 owing to the sinking of the spine due to the increased 
 weight of the abdomen. This depression of the loins 
 gives the croup bones the appearance of rising. The 
 udder of the pregnant animal is not materially changed 
 during the initial stages of gestation, but during the later 
 stages this organ gradually expands and the teats become 
 larger. A short time before parturition the udder be- 
 
68 ' THE BREEDING OF ANIMALS 
 
 comes greatly swollen and a waxy substance exudes from 
 the ends of the teats. In the cow the developing foetus 
 may be observed externally after the fifth month of preg- 
 nancy. If the cow is permitted to take a drink of very 
 cold water, the movements of the young calf may be felt 
 by pressing the hand against the flank just in front of 
 the stifle. In the mare the same movements of the un- 
 born foal may be observed from the seventh to the eighth 
 month in a similar manner by pressing the hand firmly 
 against the flank in front of the left stifle. 
 
 65. Physical examination for pregnancy. — The exist- 
 ence of pregnancy may be determined with considerable 
 accuracy by examination through the rectum. The 
 method of making this examination is described in such 
 an admirable manner by Law ^ that it is quoted entire : 
 '' Examination of the uterus with the oiled hand intro- 
 duced into the rectum is still more satisfactory, and if 
 cautiously conducted no more dangerous. The rectum 
 must be first emptied and then the hand carried forward 
 until it reaches the front edge of the pelvic bones below, 
 and pressed downward to ascertain the size and outline 
 of the womb. In the unimpregnated state the vagina 
 and womb can be felt as a single rounded tube, dividing 
 in front to two smaller tubes (the horns of the womb). 
 In the pregnant mare not only the body of the womb is 
 enlarged, but still more so one of the horns (right or left), 
 and on compression the latter is found to contain a hard, 
 nodular body, floating in a liquid, which in the latter 
 half of gestation may be stimulated by gentle pressure 
 to manifest spontaneous movements. By this method the 
 presence of the foetus may be determined as early as the 
 
 1 Law, "Diseases of the Horse," U. S. Department of Agri- 
 culture, p. 155. 
 
GESTATION AND LACTATION 69 
 
 third month. If the complete natural outHne of the virgin 
 womb cannot be made out, careful examination should 
 always be made on the right and left side for the enlarged 
 horn and its living contents. Should there still be diffi- 
 culty, the mare should be placed on an inclined plane, 
 with her hind parts lowest, and two assistants, standing on 
 opposite sides of the body, should raise the lower part of 
 the abdomen by a sheet passed beneath it. Finally the ear 
 or stethoscope applied on the wall of the abdomen in front 
 of the stifle may detect the beating of the foetal heart (one 
 hundred and twenty-five per minute) and a blowing sound 
 (the uterine sough), much less rapid and corresponding to 
 the number of the pulse of the dam. It is heard most 
 satisfactorily after the sixth or eighth month and in the 
 absence of active rumbling of the bowels of the dam." 
 
 66. The period of gestation. — The period of develop- 
 ment from the fertilization of the egg by the sperm-cell 
 until the birth of the fully developed offspring capable 
 of independent existence outside the body of the mother 
 is known as the period of gestation. Among oviparous 
 animals it is the period of incubation. This period varies 
 greatly as between different species, but under normal 
 conditions is fairly uniform in animals belonging to the 
 same species. The normal period of gestation has in 
 general a more or less definite relation to the size of the 
 animal. The length of gestation in animals as reported 
 by various authors ^ is as follows : 
 
 iNathusius, "Zool. Garten Jahrg.," 3, 1862. 
 
 Heape, "The Sexual Season," Quarterly Journal of Micro- 
 scopical Science, vol. 44, 1900. 
 
 Ewart, "The Development of the Horse," Quarterly Journal 
 of Microscopical Science. 
 
 Wortley Axe, "The Mare and the Foal," Journal of the Royal 
 Agricultural Society, 3d series, vol. IX, 1898. 
 
70 THE BREEDING OF ANIMALS 
 
 Elephant 20 to 23 months 
 
 Giraffe 14 months 
 
 Dromedary 12 months 
 
 Buffalo 10 to 12 months 
 
 Camel 13 months 
 
 Jennet 12 months 
 
 Seal 11 to 12 months 
 
 Mare 11 to 12 months 
 
 Zebra and Celtic Pony .... 334 to 338 days 
 
 Prjewalsky's Horse 356 to 359 days 
 
 Cow 9 months 
 
 Bear 6 months 
 
 Reindeer 8 months 
 
 Monkeys 7 months 
 
 . Sheep and Goat 21 to 22 weeks 
 
 Sow 4 months 
 
 Lion 3^ months 
 
 Dog 59 to 63 days 
 
 Fox and Wolf 63 to 63 days 
 
 Guinea Pig 61 days 
 
 Cat 63 days 
 
 Polecat 40 days 
 
 Rabbit 30 days 
 
 Squirrel and Rat 28 days 
 
 Mice 21 days 
 
 Small breeds require a shorter time than larger breeds, 
 but this influence may be overcome in breeds which have 
 long been selected for early maturity. According to 
 Youatt/ all domestic animals are subject to considerable 
 variation in the length of gestation both above and below 
 the normal period. Tessier ^ has observed a large num- 
 ber of pregnant females among the domestic animals 
 and has reported marked variations in the time required 
 for complete development of the foetus and final expul- 
 sion from the uterus. This authority has reported on 
 582 mares in which the period of gestation ranged from 
 
 1 Youatt, "Cattle," p. 521. 
 
 2 Tessier, "Recherches sur la Duree de la Gestation," Mem. 
 de I'Acad. des Science, Paris, 1817. 
 
GESTATION AND LACTATION 
 
 71 
 
 287 to 419 days. Among 1131 cows the length of the 
 period varied from 240 to 321 days. The minimum gesta- 
 tion period among 912 sheep was 146 days and the maxi- 
 mum 161 days. It is of interest to note, however, that 
 among 676 ewes the period varied from 150 to 154 days 
 only. 
 
 The Earl of Spencer ^ found the period to vary from 
 220 to 313 days in cows. The following table includes 
 the observations of a number of investigators and is useful 
 as indicating the somewhat wide variations which may 
 occur in the gestation period of the domestic animals : 
 
 Period of Gestation in Domestic Animals ^ 
 
 Mares 
 
 Mares 
 
 Cows 
 
 Cows 
 
 Cows 
 
 Cows 
 
 Cows 
 
 Ewes 
 
 Ewes 
 
 Sows 
 
 Sows 
 
 numbek of 
 Cases 
 
 582 
 
 25 
 
 575 
 
 764 
 
 50 
 
 98 
 
 182 
 
 912 
 
 420 
 
 25 
 
 10 
 
 Maximum 
 Days 
 
 419 
 367 
 299 
 285 
 291 
 299 
 296 
 161 
 156 
 123 
 116 
 
 Minimum 
 Days 
 
 287 
 324 
 240 
 220 
 268 
 276 
 280 
 146 
 143 
 109 
 101 
 
 Authority 
 
 Tessier 
 
 Gayot 
 
 Tessier 
 
 Spencer 
 
 Allen 
 
 Bement 
 
 Wing 
 
 Tessier 
 
 Magne 
 
 Tessier 
 
 Fox 
 
 1 Journal of the Royal Agricultural Society, vol. I, pp. 166, 167. 
 
 2 See Tessier, Journal of the Royal Agricultural Society, vol. I, 
 pp. 166, 167. 
 
 Franc k-Albrecht-Goring, " Die Trachtigkeitsdauer," Thier- 
 artzliche Geburtshiilfe, vol. 4, 1901. 
 
 Wing, Cornell Experiment Station, Bui. 162. 
 Smith, "Physiology of the Domestic Animals." 
 Allen, "American Cattle," p. 259. 
 Miles, "Stock Breeding," 1907, p. 400 et seq. 
 
72 THE BREEDING OF ANIMALS 
 
 The period of gestation in the domestic jennet is 
 370 days. Careful records kept by Kalo Monsees ^ 
 on the large jack- and jennett-breeding farm of Monsees 
 and Sons at Smithton, Missouri, indicates that the maxi- 
 mum gestation period for a living colt was 13 months 
 and 16 days. The minimum period was 11 months and 
 15 days. The average period was 370 days. These 
 figures may be taken as reliable since they cover a large 
 number of animals of varying ages and sizes for several 
 years and represent the progeny of different jacks. 
 
 67. Causes of variation in length of gestation period. — 
 The causes of variations in the time required for the 
 development of the young in the uterus are not always 
 clearly apparent. It is probable that prolonged gesta- 
 tion may sometimes be due to the mother suckling young 
 during pregnancy, resulting in providing an insufficient 
 supply of food to the developing foetus.^ Tessier con- 
 cludes that the length of the period of gestation does 
 not depend upon age, constitution of the female, diet, 
 breed or season. Nathusius ^ and others have found 
 that comparing races and breeds belonging to the same 
 species, those which have been selected for their early 
 maturing qualities have a shorter gestation period. 
 Darwin '* has given some evidence of this in connection 
 with the grading up of Merino sheep bred to the earlier 
 maturing Southdown. The length of gestation is given 
 as follows : 
 
 ^ Kalo Monsees, "Breeding Records of Monsees and Sons Jack 
 and Jennett Breeding Farm." 
 
 2 Pinard, "Gestation," Richets Dictionnaire de Physiologie, 
 vol. 7, Paris, 1905. 
 
 ' Loc. cit. 
 
 ^ Dar^vin, "Animals and Plants under Domestication," vol. 
 1, p. 123. 
 
GESTATION AND LACTATION 73 
 
 Merinos 
 
 Southdowns 
 
 Half blood Merino and Southdown 
 Three quarter blood Southdown . 
 Seven eighths blood Southdown . 
 
 150.3 days 
 
 144.2 days 
 
 146.3 days 
 145.5 days 
 144.2 days 
 
 Some doubt has been expressed as to the authenticity 
 of the maximum period of gestation in mares. The edi- 
 tor of the Breeder's Gazette commenting on this fact says, 
 "Mares are usually credited with pregnancy lasting eleven 
 months. When they run twelve months we prefer to 
 believe that the date has not been properly kept. We 
 believe that forty-eight weeks, seven days to the week, or 
 326 days is about the average duration of pregnancy in 
 a mare.'' ^ Referring to this statement M. W. Johnson ^ 
 of Illinois writes that he has been in the breeding business 
 for fourteen years and has complete records on the breed- 
 ing of 5000 mares. He reports one mare as having carried 
 her foal for twelve months and sixteen days and another 
 for twelve months and eighteen days. Both foals were 
 deformed. Another mare gave birth to a perfectly 
 healthy foal at the end of one year and eighteen days while 
 another carried her foal exactly thirteen months and 
 dropped a healthy foal. A Percheron mare belonging to 
 H. F. Sperry ^ dropped a mule colt twelve months and 
 two days after breeding. William Lokings of South 
 Dakota owned a pony mare which was twice bred and 
 gave birth to a foal twelve months and twenty-five days 
 after the last service. There is a popular belief that 
 male offspring are carried longer than female. Bement ^ 
 found that the average length of gestation for male calves 
 
 1 Breeder's Gazette, May 15, 1907. 
 
 2 lUd., June 19, 1907. 
 
 3 Ibid., June 26, 1907. 
 
 4 The Cultivator, 1845, p. 207. 
 
74 THE BREEDING OF ANIMALS 
 
 was 288 days and for females 283 days, but in 1839 the 
 female calves were carried longer than the males. Earl 
 Spencer ^ also believed there was some relation between 
 sex and the length of gestation. M. Magne ^ found the 
 period of gestation longer for ewe lambs than for ram 
 lambs. C. U. Connellee ^ of Texas finds no relation be- 
 tween the sex of foals and the time required for gestation. 
 The evidence available is insufficient to justify the belief 
 that male offspring are carried longer than females. 
 
 68. Incubation. — The period of incubation in fowls 
 represents in oviparous animals the phenomenon of gesta- 
 tion in mammals. The length of the period of incubation 
 among domestic birds is given by Miles ^ as follows : 
 
 '' Turkey, twenty-six to thirty days ; guinea hen, 
 twenty-five to twenty-six days; pea-hen, twenty-eight 
 to thirty days; ducks, twenty-five to thirty-two days; 
 geese, twenty-seven to thirty-three days ; hens, nineteen 
 to twenty-four days, or an average of twenty-one ; pigeons, 
 sixteen to twenty days; canary-birds, thirteen to four- 
 teen days. Mr. Wright remarks that ' cold weather, or 
 a prevailing east wind, will lengthen the time a day or 
 more, while warm weather and an attentive sitter will 
 hasten it ; stale eggs also hatch later than fresh.' " 
 
 The smaller breeds, like bantams, hatch in nineteen 
 or twenty days, while the heavier breeds may require 
 as long as twenty-two days for complete incubation. 
 When eggs are artificially incubated, it has been found 
 that a higher temperature combined with favorable 
 moisture conditions will shorten the period. 
 
 1 Spencer, Journal of the Royal Agricultural Society, vol. 1, 
 p. 168. 2 Loc. cit. 
 
 3 Breeder's Gazette, June 26, 1907. 
 
 4 Miles, "Stock Breeding," p. 401. 
 
GESTATION AND LACTATION 75 
 
 69. Parturition. — In mammalian animals at the end 
 of the period of gestation and in the normal course of 
 events, the fully developed foetus is expelled from the 
 uterus. This phenomenon is known as parturition. The 
 beginnings of parturition are accompanied by a series 
 of rhythmic contractions (labor pains) of the uterus which 
 eventually result in the birth of the offspring. These 
 contractions are at first partially controlled by the will, 
 but later are entirely involuntary. That the muscular 
 movements of the uterus are not controlled entirely by 
 the central nervous system is shown by the researches 
 of Kehrer,^ Helme and others. These investigators found 
 that a healthy uterus may rhythmically contract when 
 separated from the body if it is maintained at body tem- 
 perature without important variations. The powerful 
 muscular contractions of the uterus of mammals are 
 characterized by the mechanical stretching of the bag of 
 membranes by severe contraction of the longitudinal 
 muscle fibers and the relaxation of the circular fibers of 
 the cervix. The contraction of the uterus and the relaxa- 
 tion of the cervix causes the bag of membranes to act as 
 a fluid wedge still further extending the neck of the 
 womb. These phenomena are followed by the head and 
 fore legs of the young animal, the rhythmic contractions 
 become more frequent and more powerfully exerted, and 
 these are supplemented by the abdominal muscles in 
 the final stages of parturition. The immediate inciting 
 causes of parturition are not well known. Various 
 explanations have been attempted. Spiegelberg ^ has 
 suggested that the foetus secretes a substance which 
 
 1 Marshall, " The Physiology of Reproduction," p. 527. 
 
 2 Spiegelberg, "Die Dauer der Geburt," Lehrbuch der Geburts- 
 hiilfe, vol. II, 1891. 
 
76 THE BREEDING OF ANIMALS 
 
 finally entering the maternal blood reaches the nerve 
 centers and through them acts on the uterine nerves 
 in the spinal cord. Beard ^ and others have held 
 that there is an intimate relation between the oestrus 
 cycle and parturition. It is known that abortion is 
 more apt to occur at the time of the periodical return of 
 heat. But may it not be true that the period of gesta- 
 tion is itself governed by a certain rhythmic law or peri- 
 odicity similar to that which brings about the heat period ? 
 Other possible explanations are that the placenta begins 
 to decay or atrophy at the end of a given period and thus 
 loses its hold on the uterine walls, and the waste products 
 thus developed may furnish the real stimulus which 
 results in parturition.^ The death of the foetus prema- 
 turely will generally bring on expulsive movements of 
 the uterus and speedily relieve the uterus of its dead 
 burden. 
 
 It is probable that the causes of parturition are very 
 complex and that a combination of the above, together 
 with other causes, may bring about eventually the suc- 
 cessful birth of the young mammal after the normal 
 period of existence in the uterus.^ 
 
 70. Normal parturition of the domestic animals. — 
 Under ordinary conditions and in due course of time, the 
 young of the domestic animals are born without diffi- 
 culty. When difficult parturition occurs, it may be due 
 to mal-presentation of the foetus, malformation of the 
 foetus, malformation of the mother, or disease of the mother 
 preventing the normal expulsion of the foetus. 
 
 1 Beard, "The Span of Gestation and the Cause of Birth," 
 Jena, 1887. 
 
 -WilUams, "Obstetrics," London, 1904. 
 ^ See also Marshall, loc. cit. 
 
GESTATION AND LACTATION 
 
 77 
 
 71. Mal-presentations. — In order that the offspring 
 may be successfully expelled from the generative organs 
 of the mother, it is necessary that it should approach 
 the neck of the uterus in a certain form or '' presentation." 
 In all the mammalian domestic animals the normal pres- 
 entation is one in which the fore legs are extended for- 
 ward with the nose also extended forward and lying 
 between the knees. (See Fig. 11.) In case of twins, 
 
 Fig. 12. — Parturition in mare. Posterior presentation. 
 
 the second is generally presented with the hind feet first. 
 (See Fig. 12.) Any other presentation than the two here 
 described is abnormal, and the birth of young under such 
 conditions is difficult or impossible. 
 
 As most cases of difficult parturition are due to abnormal 
 presentations, it is important that the more common 
 mal-presentations should be mentioned. The more com- 
 mon and difficult mal-presentations are : — head normal, 
 but fore legs bent back at the knee (Fig. 13) ; head normal, 
 but fore legs bent back from the shoulders and entirely 
 
78 
 
 THE BREEDING OF ANIMALS 
 
 Fig. 13. — Abnormal anterior presen- 
 tation. 
 
 under the body ; fore feet normal, but head bent to one 
 side or downward ; fore legs normal, but the head bent 
 backward and upward; all four feet presented; thigh 
 and croup presented first, with hind legs bent under 
 
 body (Fig. 14) ; the back 
 first presented, with fore 
 and hind legs extending 
 backward toward the 
 uterus (Fig. 15). 
 
 72. Normal presen- 
 tations. — In the early 
 stages of parturition, 
 it is desirable to deter- 
 mine whether the foetus 
 is normally in position 
 to be expelled with least 
 difficulty. As already described, the normal presenta- 
 tion is head and fore legs forward, or in some cases 
 (twins) the hind legs forward. In making the examina- 
 tion for the purpose of determining whether the foetus is 
 in proper position, the hand and arm should be thoroughly 
 cleansed and oiled 
 with vaseline, and 
 inserted into the 
 vagina and an ex- 
 amination made. 
 The manipulation 
 should be conducted 
 with extreme gentle- 
 ness and under such conditions as shall not excite the 
 pregnant animal. Advantage should be taken of the 
 lulls in the labor pains to make the examinations. While 
 the muscular contractions are on in full force, little can 
 
 Fig. 14. — Abnormal posterior presentation. 
 
GESTATION AND LACTATION 79 
 
 be accomplished. If the foetus" is found to be normally 
 presented, it is always wise to let nature take her course, 
 and in most cases birth ensues without assistance from 
 the attendant. 
 
 73. Treatment for mal-presentation. — If the exam- 
 ination reveals the fact that the foetus is not normally 
 presented, an effort should be made to readjust the 
 
 Fig. 15. — Abnormal transverse presentation. 
 
 unborn animal so that it will be normally presented. 
 In the case of valuable breeding animals, it is generally 
 best to secure at once the services of a skilled veterinarian. 
 In attempting to make the readjustment of the foetus, 
 the same care and gentleness should be exercised as in 
 the initial examination. In order that the mal-presenta- 
 tion may be successfully adjusted and the fore legs and 
 head properly brought forward into the cervix and vagina, 
 it will be necessary to push the foetus back into the uterus 
 where there will be sufficient room for the manipulation. 
 
80 THE BREEDING OF ANIMALS 
 
 If the labor pains have already proceeded for some time, 
 it may at first be found somewhat difficult to return the 
 foetus to the uterus. In all cases it will be useless to 
 attempt to push back the unborn animal during the severe 
 labor pains. But as the resting period and consequent 
 relaxation follow each severe contraction, the foetus may 
 be gradually pushed back. It is sometimes helpful par- 
 tially to suspend the hind quarters of the pregnant mother 
 by roping the feet and hoisting the hind quarters so that 
 they will be somewhat higher than the forequarters, and 
 in this position it is generally easier to accomplish the 
 return and readjustment. In most cases in which the 
 foetus and mother are in normal health and condition, 
 the foetus may be expelled without great difficulty after 
 readjustment, that is, provided the mother has not 
 become too severely exhausted by long-continued labor. 
 In such case it is necessary to render aid by supplement- 
 ing the mother in her efforts to expel the foetus.^ 
 
 LACTATION 
 
 The young of most mammalian animals are born into 
 the world in an immature and often quite helpless condi- 
 tion. In most species the newborn animal is unfit to 
 live and thrive independently. In particular the nutri- 
 tive functions of the very young mammal are not 
 developed to a point where the individual can immedi- 
 ately exist on the food consumed by the mature parent. 
 To provide nourishment for the very young animal, all 
 mammals are provided with mammary glands which 
 secrete milk. 
 
 ^See Law, " Diseases of Cattle," 1908, and " Diseases of tlie 
 Horse," 1907, U. S. Department of Agriculture. 
 
GESTATION AND LACTATION 81 
 
 74. The mammary glands. — All mammals are supplied 
 with milk-secreting glands. These glands are present 
 in both sexes, but are rudimentary in the male. In the 
 female the glands are large and are stimulated into active 
 functioning by the exercise of the reproductive organs. 
 In the immature female before the arrival of puberty, 
 these glands are small and inconspicuous. With the 
 first appearance of puberty accompanied by the oestrum, 
 the glands increase in size. 
 
 The number of glands present varies with the species. 
 In some animals which normally give birth to one offspring 
 at a time, as in man, there are two glands (mammae). 
 In the cow, however, normally producing one at a birth, 
 the normal number of mammae is four. In cats, dogs, 
 rabbits and swine, species producing from four to twenty 
 young at one time, there are normally present several 
 pairs of mammae. Wentworth found the number of 
 mammae in swine to vary from nine to fourteen.^ There 
 is, therefore, a rather definite relation between the num- 
 ber of mammae and the normal number of young pro- 
 duced at each birth. This relation does not seem to be 
 important as an index of fertility in any particular species. 
 
 75. The duration of lactation. — Among wild forms the 
 continuance of lactation varies widely in different species. 
 In general the period of lactation ends when the young 
 animal has developed to a point where it can live in- 
 dependently and secure its nourishment in the same way as 
 the^mature individual. In the case of the domestic cow, 
 the milking function has been developed and stimulated 
 under domestication to a point where the lactation period 
 may persist from one calving period to the next without 
 
 1 Wentworth, "Inheritance of Mammae in Dm-oc- Jersey 
 Swine," American Naturalist, vol. 47, 1913. 
 
 Q 
 
82 THE BREEDING OF ANIMALS 
 
 intermission. The more important conditions which in- 
 fluence the duration of lactation and the amount of milk 
 produced among the domestic animals are food supply, 
 habit, heredity, exercise, climate and nervous excitement. 
 
 76. The food supply. — Every mature domestic animal 
 requires a certain minimum amount of food to maintain 
 the ordinary bodily functions. This is called the food 
 of maintenance. The function of milk-giving must be 
 regarded as an additional requirement. The animal, 
 therefore, that is producing milk must consume and 
 assimilate larger quantities of food than one that is dry 
 or not producing milk. It follows that the greater the 
 amount of milk produced, the larger the demands of the 
 lactating animal for food. In an ordinary cow in full 
 milk, the food of maintenance may represent sixty per 
 cent of all the food eaten. In this case forty per cent 
 of the ration is available for milk production. In a 
 heavy-producing cow, the food of maintenance may 
 represent only forty per cent of the whole. In the latter 
 case, as much as sixty per cent of the ration may be utilized 
 for milk production. The greater economy of production 
 in the case of the heavy-producing cows is at once appar- 
 ent. If an insufficient ration is fed to any cow in full 
 milk, the first effect will be to cut down the milk flow. 
 
 77. Habit. — The duration of the lactation period is 
 materially influenced by the habit of the cow as deter- 
 mined by man. The lactation period of a cow, which is 
 normally ten months, may be shortened by careless milk- 
 ing or insufficient feeding. The milking function may be 
 so stimulated by careful and thorough milking and intelli- 
 gent feeding that the daily quantity of milk may be 
 increased and the period of lactation lengthened. 
 
 78. Heredity. — The capacity to give milk in abundance 
 
GESTATION AND LACTATION 83 
 
 is hereditary. The present highly productive dairy breeds 
 owe their greater abihty to produce large quantities of milk 
 to their inheritance of this quality from their ancestors. 
 In the same breed certain families are known to possess the 
 quality of large capacity for milk production to a higher de- 
 gree than the average of the breed. It is also true that the 
 duration of the period of lactation is influenced by heredity. 
 
 79. Exercise. — An excessive amount of muscular 
 exertion of any kind must be regarded as unfavorable 
 to the maximum production of milk. Cows that are 
 required to travel long distances over sparse pastures 
 in order to secure sufficient food for their needs cannot 
 produce their maximum quantity of milk. In many 
 European countries, cows are generally employed as 
 draft animals in the ordinary farm operations of plowing, 
 harrowing, reaping and other work. Investigations in 
 Germany have shown that so long as cows are employed 
 at moderate work the milk flow is not decreased. When- 
 ever cows were compelled to work at heavy labor and 
 for long hours, invariably the flow of milk was decreased. 
 
 80. Climate. — Exposure to extreme dry cold or to cold 
 driving storms will have the effect of decreasing the normal 
 milk yield of a herd of cows. In general, a lack of ade- 
 quate shelter in a cold and humid climate may seriously in- 
 terfere with the highest development of the milking func- 
 tions. A herd of cows will produce more milk in winter 
 if provided with water which has been slightly warmed. 
 
 81. Unusual lactation. — In general, lactation is closely 
 associated with reproduction. Pregnancy followed by 
 parturition normally precedes the secretion of milk in 
 the mammary glands. Males and sterile females possess 
 rudimentary mammae but seldom secrete milk, although 
 a number of cases are on record where males have been 
 
84 
 
 THE BREEDING OF ANIMALS 
 
 known to secrete milk. The hybrid mare mule in rare 
 cases has been known to secrete milk through the excita- 
 tion of the mammary glands. In the cases observed, 
 the mammary glands have generally been stimulated 
 to secrete through the persistent suckling of some young 
 mule colt which may have been running in the same 
 pasture or lot. It is rare that the mammary glands of a 
 mare mule will develop to the point of secreting milk 
 in the absence of some such stimulation. 
 
 The author has discovered one mare mule which has 
 secreted milk without any such stimulus. This mare 
 mule belonging to L. O. Swarner of Boonville, Missouri, 
 when first observed had been giving milk for some weeks. 
 The owner in a letter to the author says : "I have a mule 
 that has been giving milk the same as a brood mare does 
 when suckling a colt. She has been giving milk for about 
 five weeks. The mule is still giving milk, as much as a 
 quart at a time. (See Plate III, upper.) The milk is pure 
 white and streams from her udder." This mare mule 
 came in heat regularly and was bred several times but 
 failed to become pregnant. The milk was analyzed by 
 the Missouri Experiment Station. The analysis is shown 
 in the table in comparison with cow's and human milk : 
 
 Composition op Milk from Mare Mule Compared with 
 Cow's AND Human Milk 
 
 
 Mare Mule 
 "Beck " 
 
 Cow's Milk 
 
 Human Milk 
 
 Water 
 
 90.441 % 
 
 87.17% 
 
 87.41 % 
 
 Total Solids 
 
 9.559 
 
 12.83 
 
 12.59 
 
 Ash 
 
 0.400 
 
 0.71 
 
 .31 
 
 Fat 
 
 1.450 
 
 3.64 
 
 3.78 
 
 Protein 
 
 2.463 
 
 3.55 
 
 2.29 
 
 Sugar 
 
 5.792 
 
 4.88 
 
 6.21 
 
Plate III. — Upper. A mare mule that gives milk. Lower. A 
 Free-Martin heifer that proved fertile. 
 
CHAPTER V 
 FERTILITY 
 
 The larger number of the breeders of domestic animals 
 are engaged merely in the multipHcation of animals. 
 They are not primarily striving for the improvement of 
 the species. To all these, the ability of an animal to 
 produce young in abundance is of fundamental impor- 
 tance. To the relatively small class of breeders who are 
 successful in really improving the desirable characteristics 
 of existing breeds, the quality of fertility is likewise of 
 primary importance. When the breeder has succeeded 
 in developing a highly improved strain, it becomes im- 
 portant to secure as many offspring possessing the new 
 and desirable qualities as possible. 
 
 Fertility may be defined as the ability of an animal 
 to produce young in abundance. This quality depends 
 upon the number of young born at one time, the fre- 
 quency of the recurrence of the oestrum, the duration of 
 the period of gestation, and the length of the period of 
 life during which reproduction occurs. All of the above 
 conditions are affected by many circumstances, some 
 external, others internal and inherent in the individual 
 and the species. Many of the circumstances influencing 
 fertility can be directly or indirectly controlled by man, 
 others are beyond his control. 
 
 82. The number of young at a birth. — There is very 
 great variation among animals in respect to the number 
 
 85 
 
86 THE BREEDING OF ANIMALS 
 
 of young born at one birth. This difference is very 
 marked, as between different species, for example, as 
 between the sow and the ewe. A similar difference is 
 likewise to be observed between individuals and families 
 belonging to the same species. In a general way, the 
 number of young carried in the uterus at one time seems 
 to depend upon the size of the animal. Thus the ele- 
 phant, rhinoceros, hippopotamus, giraffe, bison, domes- 
 tic mare and cow, produce one young at a birth. The 
 goat and sheep, while normally producing one offspring 
 at a time, may frequently produce twins and triplets or 
 even a larger number at one birth. 
 
 The hare and rabbit are much smaller than the sheep 
 and are very much more prolific. The wild rabbit pro- 
 duces from four to eight in a litter. The domestic rabbit 
 is more prolific than the wild, often giving birth to eight 
 or ten at one time. 
 
 The lion and tiger in a wild state give birth to two to 
 three cubs, while the domestic cat will sometimes produce 
 as many as nine. The size of the litter in the fox is from 
 four to eight. The number of young in the litter of the 
 domestic dog varies from five to twelve. 
 
 The domestic sow is an exception to the general rule 
 that smaller species are more prolific. The sow is the 
 most prolific of the more important domestic animals, 
 though not the smallest. The wild sow's litter numbers 
 four or five. The domestic sow produces from seven to 
 twelve, and much larger litters are common. 
 
 The smaller rodents, like the rat and mouse, are char- 
 acterized by large litters. The rat regularly gives birth 
 to twelve or fifteen young at a time and has been known 
 to produce twenty at one birth. The mouse is equally 
 prolific. 
 
FERTILITY 87 
 
 It does not seem to be generally true among domestic 
 animals that the smaller breeds are more fertile than the 
 larger breeds of the same species. Among sheep, the 
 American Merino and Southdown are relatively small 
 breeds, but are less prolific than the larger Shropshire, 
 Cotswold or Lincoln. The smaller breeds of swine, 
 like the Essex, Cheshire and Small Yorkshire, are in 
 general less prolific than the larger Berkshire, Duroc- 
 Jersey and Large Yorkshire. In this instance, it is 
 probable that selection by man has intervened to counter- 
 act the general law that the smaller animals are more 
 fecund. 
 
 83. Period of gestation and fertility. — The length of 
 the period of gestation seems to be some index of the 
 number of young produced at a birth. In all animals 
 requiring a longer period of gestation than six months, 
 one is the normal number of young at a birth. ^ Among 
 the animals in which the period is less than six months 
 are the hog, sheep, goat, rabbit, dog, cat, rat and mouse. 
 In all of these, except the sheep and goat, the normal 
 number is greater than one. The sheep and goat under 
 domestication have so increased in fertility, in the cases 
 of some breeds at least, that fecundity is much greater 
 than in the horse or cow, where single births are the rule. 
 Milch goats usually drop twins, and triplets are not rare.^ 
 
 The Border Leicester breed in England has produced 
 150 to 160 per cent of lambs under ordinary conditions. 
 When the same breed has been specially fed before breed- 
 ing, the number of lambs has been increased to 200 per 
 cent. 
 
 1 Marshall, "The Physiology of Reproduction." 
 
 2 Clos, vol. Ill, p. 410, "Cyclopedia of American Agri- 
 culture." 
 
88 THE BREEDING OF ANIMALS 
 
 84. Fertility and the frequency of the recurrence of the 
 oestrum. — The fertility of animals is also dependent 
 upon the frequency of the recurrence of the oestrum. 
 As already described, the recurrence of heat depends 
 upon a number of conditions, chief of which are 
 pregnancy and lactation. Certain of the domestic 
 animals do not normally come in heat while suckling 
 young, but to this there are many exceptions. Animals 
 having a short period of gestation rarely or never come 
 in heat while suckling young. 
 
 85. Fertility and gestation. — Animals having a long 
 period of gestation are less fertile than animals requiring 
 a shorter time for the development of the young in the 
 uterus. 
 
 The exceptional fertility of the domestic sow is due 
 not only to the large number of young born at a time, 
 but to the further fact that the period of gestation is 
 only four months. A sow may thus easily produce 
 two litters a year. The mare produces but one off- 
 spring at a time, and the period of gestation is from 
 eleven to twelve months. A sow, therefore, may give 
 birth to twenty young in the same period of time re- 
 quired by the mare for the development and birth of 
 one offspring. 
 
 86. Duration of the reproductive period. — The fertility 
 of an individual or a breed is largely determined by the 
 duration of the reproductive period. The length of 
 this period is a matter of special importance in the larger 
 animals which produce but one young at a birth. The 
 breeding age is the time from the arrival of puberty 
 until the cessation of the breeding function on account 
 of old age. The beginning of the reproductive period 
 has already been discussed under puberty. The 
 
FERTILITY 89 
 
 average age at which the domestic animals cease to 
 breed is difficult to determine because of the scarcity of 
 records on this point. The persistence of the breeding 
 powers of the domestic animal is influenced by the condi- 
 tions under which they are reared. With favorable 
 conditions, the mare has produced young regularly until 
 twenty-five years old. Ewes have continued to produce 
 offspring until nineteen years of age. 
 
 87. Confinement and fertility. — The close confine- 
 ment of animals seriously interferes with their fertility. 
 Wild animals like the elephant, tiger, lion, squirrel and 
 monkey in captivity are often sterile. Darwin states 
 that the same animals breed more readily in traveling 
 shows than in zoological gardens. Among the domestic 
 animals, confinement and lack of exercise are frequent 
 causes of a low degree of fertility. It is generally a mis- 
 take to confine ewes or sows in a small lot during the 
 winter months, under conditions which make it impossible 
 for them to secure adequate exercise. The same may be 
 said of males, including stallions, bulls, boars and rams. 
 The comparative infertility of a stallion may often be 
 traced directly to the fact that he is kept stabled in a small 
 dark stall with no regular exercise. Mares both before 
 and after breeding should be given regular exercise. It 
 is better that they should work at some slow regular task 
 every day. 
 
 In an investigation on the relation of exercise to the 
 development of the internal organs by Kulbs and Ber- 
 berrich,^ it was found that in the case of dogs and swine 
 the size of the muscles and the weight of the heart and 
 liver were increased by exercise. It was also observed 
 that the color of the bone marrow was deepened. 
 
 1 " Jahrbuch Wiss. und Prakt. Tierzucht," 6 (1911), p. 232. 
 
90 THE BREEDING OF ANIMALS 
 
 Darwin ^ reports that " It has been found in France 
 that with fowls allowed considerable freedom, only twenty 
 per cent of the eggs failed ; when allowed less freedom, 
 forty per cent failed ; and in close confinement, sixty out 
 of the hundred were not hatched." 
 
 88. The fertility of domesticated animals. — From 
 what has already been said regarding confinement and 
 its deleterious effect on fertility, it might be concluded 
 that domestication is unfavorable to high fertility in 
 animals. This is far from the truth. Domestication 
 furnishes or ought to furnish the most favorable conditions 
 for high fertility in animals. A regular and abundant 
 supply of nutritious food, shelter from a rigorous climate, 
 and the opportunity for selection by man all contribute 
 to the development of a relatively high degree of fer- 
 tility in animals. All races of domestic animals are more 
 fertile than their wild prototypes. Darwin has pointed 
 out that the tame rabbit gives birth to four to eleven in 
 a litter and breeds six or seven times a year, while the 
 wild rabbit only produces five or six young at one time 
 and breeds four times yearly. The domestic fowl may 
 produce as many as 200 or more eggs in one year, while 
 the female of the wild progenitor of the domestic hen lays 
 only six to ten eggs in a year. The same remarkable 
 difference exists between the domestic and wild duck. 
 The Indian Runner duck under domestication will pro- 
 duce 250 eggs a year, and the wild duck only five to ten 
 eggs in one year. At the Government Experiment 
 Station of New South Wales in Australia, six Indian 
 Runner ducks laid 1601 eggs in one year, an average of 
 267 eggs each. 
 
 1 Darwin, "Animals and Plants under Domestication," 
 vol. IT. 
 
FERTILITY 91 
 
 89. Age and fertility. — The fertility of animals is 
 influenced by age. Young animals that have not yet 
 reached maturity are generally less fecund than mature 
 individuals. There is also some evidence to show that 
 old mature animals are more prolific than younger mature 
 animals. It is highly probable that skillful feeding and 
 management may result in a significant increase as age 
 advances. 
 
 90. Relation of age to fertility in swine. — At the 
 Missouri Experiment Station, the author has had under 
 investigation the relation of the age of animals to their 
 breeding powers. The animals used in this experiment 
 have been swine, and the general plan has been to divide 
 the sows into three groups according to age. Group I 
 is composed of very young sows from four to five months 
 of age; group II of half mature sows about eighteen 
 months of age ; and group III of mature sows from twenty- 
 four to thirty months old. The young immature sows 
 of group I have been bred at the first appearance of 
 puberty, which in well-fed sows is from four to five months 
 old. The female offspring of the immature sows are 
 again bred at the first appearance of heat, and this will 
 be continued indefinitely. A number of interesting 
 phenomena have been observed, but only those results 
 which throw light on the relation of age to the fertility 
 of the mother are recorded here. 
 
 91. Influence of age of sow on size of litter. — In 
 the Missouri experiment described above, there have 
 been to date (1913) twentj^-six litters from immature 
 sows. The average number of pigs to the litter has been 
 four and eight-tenths. From the half mature sows, 
 eight litters have resulted in an average of six and three- 
 tenths to a litter. The average number of pigs in six 
 
92 THE BREEDING OF ANIMALS 
 
 litters from the fully mature sows has been six and five- 
 tenths. 
 
 The sows used in this experiment were all of the same 
 breeding, and received the same care, and the food, shelter 
 and all other conditions have been similar. The differ- 
 ences observed then must be due to the factor of age. 
 It will be observed that there is a marked difference 
 between the size of the litters of the immature sows and 
 the older ones. The litters of the older sows are materi- 
 ally larger than from the immature sows. 
 
 The highest fertility in swine is not reached until the 
 mother is at or near maturity. It may not always be 
 profitable for the swine-breeder to delay breeding sows 
 until full maturity, T^ut it is apparent that when the breed- 
 ing herd is composed of older sows, a smaller number 
 need be maintained for the production of the pigs needed 
 in a given system of farm management. 
 
 Interesting statistics have been compiled by George 
 M. Rommel ^ from the records of the American Poland- 
 China Record Association, which have an important 
 bearing on this point. These statistics include the breed- 
 ing records of 6145 sows recorded in 1902. There were 
 examined the breeding records of 2010 one-year old sow^. 
 The litters of 1520 one-year-old sows, or seventy-five per 
 cent, ranged from five to eight pigs. 
 
 The average litter of 2047 two-year-old sows numbered 
 seven and five-tenths. The number in each litter of 
 1483 sows, or seventy-two per cent, ranged from six to 
 nine pigs. 
 
 The average number of pigs in the litters of 1157 
 three-year-old sows was seven and nine-tenths. The 
 average litter recorded for 606 four-year-old sows was 
 
 1 American Breeders' Association, Report 19. 
 
FERTILITY 
 
 93 
 
 eight and three-tenths. The records for 325 five-year- 
 old sows give the average size of Htter as eight and seven- 
 tenths. The total number of sows examined, ranging 
 in age from one to five years, was 6145 and the average 
 size of litter for the whole number was seven and four- 
 tenths. 
 
 The number of animals included in these investiga- 
 tions and the unquestioned accuracy of the records make 
 these figures valuable. It is clear that the sows increase 
 in fertility from one to five years. From the standpoint 
 of the practical breeder, it would seem that sows from 
 two to four years of age will be most profitable from the 
 standpoint of prolificacy. 
 
 92. Relation of age to fertility in sheep. — The greater 
 fertility of the older females has been noted in ewes by 
 the Wisconsin Experiment Station in Bulletin No. 95. 
 Observations made at that station on the percentage of 
 increase from ewes of different ages show that two-year- 
 old ewes gave an annual increase of 158 per cent, three- 
 
 The Effect of the Age of Ewes on Per Cent of In- 
 crease AND Sex op Lambs 
 
 WISCONSIN experiment STATION, BULLETIN 95 
 
 Age of Ewe 
 
 Two 
 Years 
 
 Three 
 
 Years 
 
 Four 
 Years 
 
 Five 
 
 Years 
 
 Six 
 Years 
 
 Seven 
 Years 
 
 Bearing 
 
 No. 
 
 Per 
 cent 
 
 No. 
 
 30 
 
 58 
 
 6 
 
 75 
 
 72 
 
 Per 
 cent 
 
 No. 
 
 Per 
 cent 
 
 No. 
 
 Per 
 cent 
 
 No. 
 
 Per 
 
 cent 
 
 No. 
 
 Per 
 cent 
 
 Single Lambs . 
 Pairs Twins . 
 Sets Triplets . 
 Rams. . . . 
 Ewes .... 
 
 62 
 
 72 
 
 4 
 
 96 
 
 100 
 
 44.6 
 52.5 
 2.9 
 49.0 
 51.0 
 
 31.9 
 61.7 
 6.4 
 51.0 
 44.0 
 -S 
 
 21 
 42 
 6 
 71 
 53 
 
 30.4 
 60.8 
 
 8.8 
 57.2 
 42.8 
 
 14 
 32 
 3 
 45 
 42 
 
 28.5 
 65.3 
 6.2 
 51.7 
 48.3 
 
 9 
 15 
 
 3 
 24 
 21 
 
 33.3 
 55.5 
 11.2 
 53.3 
 
 46.7 
 
 6 
 3 
 1 
 10 
 5 
 
 60.0 
 30.0 
 10.0 
 66.7 
 33.3 
 
 Per cent 
 increase . . 
 
 158.0 
 
 174.0 
 
 178.0 
 
 177.0 
 
 178.0 
 
 150.0 
 
94 THE BREEDING OF ANIMALS 
 
 year-old ewes an increase of 174 per cent, and four- to 
 six-year-old ewes an increase of 178 per cent. After 
 the age of six years, there w^as a distinct falling off in the 
 percentage of increase. 
 
 The foregoing table (page 93) is reprinted entire from 
 the Wisconsin bulletin and is interesting as showing the 
 distribution of twin and triplet births among the different 
 ages and the sex of lambs. 
 
 93. Influence of age of ram on fertility of ewes. — 
 The number of young at a birth is generally believed 
 to be determined by the number of ova which are ripened 
 by the female during any one period of heat. The vigor 
 or age of the male used is not generally regarded as hav- 
 ing any influence in determining the number born at 
 one time. The Wisconsin Station ^ found that during 
 a period of six years, the flock of ewes served by a year- 
 ling ram produced 150 per cent of lambs. The same 
 flock during a similar period of six years was served for 
 three of these years by two- and three-year-old rams. 
 The average percentage of lambs born from the older 
 rams was 180 per cent. The author in discussing these 
 results remarks : " These data are quite at a variance 
 with the opinion commonly held by sheepmen, generally 
 to the effect that a well grown, vigorous yearling ram 
 is at his best as a sire. It is also contrary to the belief 
 held by many that the vigor of the sire has no apparent 
 influence on the percentage of increase." 
 
 94. The effect of the age of poultry parents on the 
 offspring. — The general conclusion that fully mature 
 animals are more fertile seems to be substantiated by 
 the poultry-breeding experiment conducted by Atwood.^ 
 
 1 Wisconsin Experiment Station, Bulletin 95. 
 
 2 Atwood, West Virginia Experiment Station, Bulletin No. 124. 
 
FERTILITY 
 
 95 
 
 
 
 
 
 
 to 
 
 
 5" 
 
 
 lO CO 1 CO 
 
 rn 
 
 CO 
 
 
 CO 
 l> 
 
 CO l> 1 t:}5 
 
 to 
 
 00 T*H 
 
 
 ^'^ 
 
 CO 
 
 1-; CO 1 
 
 CO 
 
 CO 
 CO CO 
 
 
 <! 
 
 lO 
 
 c<i d 1 CO 
 
 CO 
 
 l> to 
 
 
 
 l> 
 
 T-l 1— 1 lO 
 
 t^ 
 
 
 
 ^i-" 
 
 
 00 1 CO 
 
 TJ^ 
 
 to t> 
 
 
 <1 
 
 o 
 
 rH lO 1 t>I 
 
 CO 
 
 I> (M 
 
 
 
 CO 
 
 >— 1 r-l LO 
 
 l> 
 
 1— ( 
 
 
 
 
 l> 
 
 
 
 
 
 
 q 1 
 
 "^ 
 
 o 
 
 
 a( 
 
 I> 
 
 CO 00 1 Oi 
 
 00 
 
 00 CO 
 
 M 
 
 
 lO 
 
 i-i CO 
 
 CO 
 
 
 
 
 "* 
 
 
 
 to 
 
 (3 
 
 
 ^ 1 
 
 CO 
 
 1—1 
 
 « 
 
 d^*^ 
 
 lO 
 
 (N l> 1 CO 
 
 CO 
 
 b- 1-1 
 
 H 
 
 
 iO 
 
 1— i Tf 
 
 00 
 
 1> 
 
 
 
 T— 1 
 
 
 TtH 
 
 
 «<^ »H 
 
 
 <M 1 
 
 00 
 
 CO 
 
 
 Ph 
 
 1—1 
 
 (M" 00 1 1-1 
 
 1— t 
 
 t> to 
 
 
 
 l> 
 
 rH 1—1 lO 
 
 t^ 
 
 
 
 
 
 CO 
 
 
 o 
 
 
 C3 
 
 
 r-< 
 
 r-i 
 
 to 
 
 
 Pm 
 
 00 
 
 CO a l^ -rH 
 
 l> 
 
 00 CO 
 
 <N 
 
 
 00 
 
 T— 1 CO 
 
 o 
 
 
 
 
 (M 
 
 
 to 
 
 H 
 
 « N 
 
 
 (M 
 
 to 
 
 l> 
 
 H 
 
 Ph 
 
 (M 
 
 (M lO tH (N 
 
 o 
 
 l> I> 
 
 H 
 
 
 05 
 
 T— 1 1— 1 CO 
 
 t- 
 
 
 
 
 1—1 
 
 
 "* 
 
 
 fl 
 
 
 t^ 
 
 l> 
 
 CO 
 
 
 Ph 
 
 Tj< 
 
 1-5 oi 1 CO 
 
 CO 
 
 l> (N 
 
 
 
 tH 
 
 1—1 1—1 O 
 
 CO 
 
 1—1 
 
 
 
 1—1 
 
 
 
 
 
 
 
 Oi 
 
 
 t^ 
 
 
 
 
 (N 
 
 1—1 
 
 Tt^ 
 
 
 Ph 
 
 ^ 
 
 Tt^ to Oi O 
 
 1—1 
 
 00 CO 
 
 i-H 
 
 
 l> 
 
 1— t CO 
 
 00 
 
 
 
 
 00 
 
 
 th 
 
 fH 
 
 « « 
 
 
 1—1 
 
 Oi 
 
 to 
 
 H 
 
 Ph 
 
 Oi 
 
 (M OS O O 
 
 to 
 
 1> 00 
 
 H 
 
 
 t> 
 
 1— I 1—1 CO 
 
 t^ 
 
 
 
 
 to 
 
 00 
 
 CO 
 CO 
 
 
 pL, 
 
 lO 
 
 1-1 00 (M to 
 
 1—1 
 
 l> T-l 
 
 
 
 lO 
 
 1— t r^i 
 
 00 
 
 (N 
 
 
 
 !=i ■ 5;^ 
 
 ■ ' "^ ' J^ 
 
 • M 
 
 JH 1 . . 
 
 
 
 -M , ft 
 
 
 
 is ■ ' 
 
 
 
 M bo 
 bi} be 
 
 \£-|^«-2 
 
 
 
 
 &J0 • <D 
 
 . ^ ^ ^ O 
 
 ® rJd XJ O • II 
 
 
 
 er of e 
 bator 
 t of 
 
 lbs. 
 out i 
 ched c 
 er of c 
 nt hat 
 
 c3 «4-H 
 ;- O 
 o 
 
 100 1 
 en fr 
 r . 
 ieaths 
 
 
 
 rQ 3^ 
 
 ,^ ^^ -i^ r) O 
 
 ■^ rd 
 
 03 c3 c3 ^ 
 
 
 
 a ^.^ 
 
 ^:§ 
 
 
 
 
 
 o o 
 
 ft HJ ^ *^ 
 
 
 
 ^ 
 
 d 
 ;h 
 o 
 
 a 
 
 o 
 
 o 
 
 »o 
 
 1—3 
 
 o 
 
 > 
 
 o 
 
 • l-H 
 
 eg 
 
 • pH 
 
 o 
 o 
 
 <D 
 <D 
 t-l 
 
 pq 
 d 
 
 c3 
 o 
 
 • 1— ( 
 
 <D 
 
 a 
 
 
 So o 
 WW 
 
 (N CO 
 
 73 
 CD d d d 
 
 fn 03 <I> 0) 
 
96 THE BREEDING OF ANIMALS 
 
 In this investigation, Single Comb White Leghorns were 
 employed and a comparison of hens, pullets, two-year 
 and three-year-old hens was made. The important results 
 may be seen at a glance from the table (page 95). 
 
 The records of this test show that the eggs laid by old 
 hens are heavier than those laid by pullets, that the num- 
 ber of chicks hatched was ten per cent greater, that the 
 initial weight at hatching time, and for several weeks 
 thereafter, was greater from the older hens, and finally 
 that the percentage of chicks dying from pullet's eggs 
 was three times greater than from the mature hens. 
 
 In marked contrast to the above results are those 
 published by the Maine Experiment Station in Bulletin 
 168. The author (Pearl) of this publication states, 
 " The present statistics do not show any marked superi- 
 ority of hens over pullets in respect to breeding perform- 
 ance, so far as either fertility or hatching quality of eggs 
 are concerned." 
 
 95. Age and fecundity. — Duncan ^ distinguishes be- 
 tween the ability to bear children, which he calls fecundity, 
 from actual productiveness or the number of births, which 
 is designated as fertility. From Duncan's investigations 
 it is possible to formulate a general law which represents 
 a true statement of the relation of age to fecundity. This 
 general law has been stated by Marshall ^ as follows : 
 " The fecundity of the average individual woman may be 
 described, therefore, as forming a wave, which, starting 
 from sterility, rises somewhat rapidl}' to its highest point 
 and then gradually falls again to sterility." The results 
 discussed earlier in this chapter clearly indicate that in 
 
 1 Duncan, "Fecundity, Fertility, Sterility and Allied Topics," 
 Edinburgh, 1866. 
 
 2 Marshall, "The Physiology of Reproduction," p. 590. 
 
FERTILITY 
 
 97 
 
 the case of swine this law is undoubtedly a true statement 
 of what actually happens. This law not only applies 
 to mammals but is also found in poultry. Geyelin ^ has 
 attempted to formulate an average of fertility in poultry 
 in relation to age in the following table : 
 
 First Year after hatching . 
 Second Year after hatching 
 Third Year after hatching . 
 Fourth Year after hatching 
 Fifth Year after hatching . 
 Sixth Year after hatching . 
 Seventh Year after hatching 
 Eighth Year after hatching 
 Ninth Year after hatching . 
 
 15 to 
 
 100 to 
 
 120 to 
 
 100 to 
 
 60 to 
 
 50 to 
 
 35 to 
 
 15 to 
 
 1 to 
 
 20 eggs 
 
 120 eggs 
 
 135 eggs 
 
 115 eggs 
 
 80 eggs 
 
 60 eggs 
 
 40 eggs 
 
 20 eggs 
 
 10 eggs 
 
 These estimates must be regarded as far below the 
 performance of well-selected flocks maintained under 
 good conditions of food and shelter. The age at which 
 pullets begin laying varies greatly, depending upon their 
 development. At the Ohio Experiment Station, a White 
 Leghorn pullet began laying at four months and fifteen 
 days old. At the Missouri Experiment Station Kempster ^ 
 reports a White Leghorn pullet beginning to lay at four 
 months and nineteen days of age. The number of eggs 
 laid by old hens may also greatly exceed the figures given 
 by Geyelin. At the Maine Experiment Station a hen 
 laid 111 eggs during her ninth year.^ 
 
 A remarkable case of fecundity in sheep is noted by 
 Pearl.^ A ewe owned by Barrett for nineteen years 
 gave birth to thirty-six lambs which were distributed 
 during the breeding life of the ewe as follows (page 98) : 
 
 ^ Geyelin, quoted by Marshall, loc. cit., p. 590. 
 
 2 Unpublished records, Missouri Experiment Station. 
 
 ^ Maine Experiment Station, Bulletin 266. 
 
 * Pearl, Science, vol. 37, p. 227. 
 
 H 
 
98 THE BREEDING OF ANIMALS 
 
 LAMBS 
 
 April, 1806 1 
 
 1807 1 
 
 1808 2 
 
 Aprils, 1809 3 
 
 March 29, 1810 3 
 
 Making 6 lambs in 11 months and 26 days 
 
 1811 3 
 
 1812 3 
 
 1813 3 
 
 1814 3 
 
 1815 2 
 
 1816 2 
 
 1817 2 
 
 1818 2 
 
 1819 2 
 
 1820 2 
 
 1821 1 
 
 1822 1 
 
 1823 
 
 1824 _0 
 
 Total 36 
 
 Pearl has further called attention to the fact that 
 '^ the median point in the breeding career of this ewe was 
 8.17 years. That is, she produced one-half of her offspring 
 before and one-half after it." The age of maximum fe- 
 cundity in this ewe was 7.34 years. 
 
 96. Nutrition and fertility. — All the physiological 
 activities of an animal are influenced by nutrition. This 
 is particularly the case with the reproductive functions. 
 The fertility of an animal is influenced by the kind and 
 the amount of food consumed. Certain kinds of food 
 have long been believed to affect injuriously the breeding 
 functions of animals. Sugar fed to domestic animals 
 in considerable amounts has apparently had an unfavor- 
 able influence on fertility.^ Greatly increased activity 
 
 1 Tanner, Journal of Royal Agricultural Society, 1865, p. 267. 
 
FERTILITY 99 
 
 of the generative organs is characteristic of the spring 
 season. At this season most animals, domestic and wild, 
 are periodically in heat. This greater activity is un- 
 doubtedly due to the abundant supply of nutritious and 
 succulent grass. That this kind of food does materially 
 influence the fertility of animals is recognized by the 
 shepherds of England in the practice of flushing ewes. 
 This practice consists in turning the ewe flock on rich 
 succulent pastures about two weeks before turning in 
 the ram. The flock owners believe that this increases 
 the number of lambs and brings the ewes more uniformly 
 in heat. The Beinn Bhreagh ^ flock of sheep in Nova 
 Scotia belonging to Dr. Bell when fed generously before 
 and during the mating season produced a larger number 
 of twins. The older ewes also produced a larger per- 
 centage of twins. 
 
 97. Excessive food supply and nutrition. — An over- 
 supply of nutritious food which causes the animal to 
 become abnormally fat is often the cause of sterility 
 among the domestic animals. In nature it is rare for 
 an animal to remain continuously in an excessively fat 
 condition. At certain seasons of abundant food supply 
 the wild animal may become fat, but such periods of 
 plethora are invariably followed by a scarcity of food, 
 and such food must often be gathered by exhaustive 
 exercise. Such variations, if not extreme, may be partic- 
 ularly favorable for the functioning of the reproductive 
 system. Certain it is that the most skillful stockmen 
 have long recognized the fact that the female reproduc- 
 tive functions are most active when the individual is 
 actually gaining in condition. An animal that is main- 
 tained in a uniform condition of excessive fatness is not 
 
 ^ Bell, Journal of Heredity, vol. V, p. 47. 
 
100 THE BREEDING OF ANIMALS 
 
 in the best condition for the successful exercise of the 
 breeding function. A rapidly improving condition due 
 to nutritious food supplied in generous quantities is 
 distinctly favorable, provided the animal is not already 
 too fat. 
 
 E. Davenport has held that, " excessive food supply 
 leads to infertility among both plants and animals.'' 
 This is true of long-continued and excessive feeding, but 
 a rapidly improving condition of the animal in thin condi- 
 tion is distinctly favorable to the highest fertility. It is 
 a mistaken idea that starvation or a very limited diet 
 is a favorable environment for the successful activity of 
 the generative system. Such treatment is only favorable 
 in the case of over-fat animals and is oftener the first 
 and a very essential step in securing offspring from animals 
 that through a long period of overfeeding become tem- 
 porarily barren. 
 
 98. Other factors affecting fertility. — A sudden change 
 of conditions surrounding the animal, such for example 
 as the exportation of an animal from Europe to the United 
 States, will often temporarily interfere with the normal 
 activities of the reproductive system and the animal 
 may be barren for a time. When' the animal has become 
 thoroughly accustomed to the changed conditions, its 
 breeding powers return and thereafter may function 
 normally. Changed conditions may also result in in- 
 creased fertility. As shown elsewhere, breeding animals 
 in thin condition and existing upon a sparse ration or upon 
 a dry dietary, become markedly more fertile when changed 
 to richer pastures. 
 
 Some individuals are infertile when mated with cer- 
 tain other individuals, but may be fully fertile with others. 
 A mare may be sterile when bred to a stallion, but fertile 
 
FERTILITY 101 
 
 when mated with a jack. Such a physiological aversion 
 is not easy to explain, but is nevertheless so frequent as 
 to be a well-recognized fact among breeders. Prolonged 
 lactation must be regarded as unfavorable to fecundity 
 in some species. This is especially true in the case of 
 swine, where early weaning of the litter will certainly 
 encourage an earlier return of the heat period and thus 
 make possible a larger number of litters during the natural 
 breeding life of the mother. 
 
 99. Relation of number of mammae in swine to fertility. 
 — An interesting study of the mammae in swine was 
 reported by Wentworth.^ From these researches there 
 is little evidence in favor of the popularly accepted opinion 
 that there is a relation between the fertility of swine and 
 the number of mammse. The normal type of mammary 
 pattern in swine consists of regularly placed pairs on the 
 ventral side of the body. The first pair lie immediately 
 behind the juncture of the ribs and sternum. The 
 greatest variation occurs in the second pair. The last 
 pair are closer together and thus nearer the median line 
 in an inguinal position. Variations occur in the number 
 of pairs and also in the suppression of one nipple of a 
 pair. These variations are often inherited. The normal 
 number of mammse in the Tamworth and Berkshire 
 breeds is 13, 14 and 15, in the Duroc-Jersey breed 10, 
 11 and 12. The tendency to vary is greater when the 
 number of pairs exceeds five. 
 
 100. Twins. — The normal number of young in several 
 of the larger breeds of the domestic animals and in man 
 is one. The production of a larger number at a single 
 birth is exceptional. It happens, however, that twins 
 are frequently born, while triplets and even four and 
 
 1 Wentworth, Amer. Naturalist, vol. 47, p. 257. 
 
102 THE BREEDING OF ANIMALS 
 
 five at a birth have been reported. When twins are 
 born they are either of identical sex or one a male and 
 the other a female. In some cases the twins are very 
 much alike in all other characters as well as sex. Such 
 twins were called by Galton identical twins. It is also 
 true that twins are often born which have no greater 
 resemblance to one another than ordinary brothers and 
 sisters. Such twins undoubtedly develop from separate 
 eggs and are known as ordinary or fraternal twins. They 
 do not necessarily resemble one another more closely 
 than brothers and sisters of the same family except 
 that they are of identical age and for this reason might 
 be expected to have a closer resemblance than brothers 
 or sisters of widely different ages. Fraternal twins may 
 be of different sex. Identical twins are believed to come 
 from one egg after fertilization. They are always of the 
 same sex and very much alike in external and internal 
 character and in mental and moral tendencies. 
 
 101. Characters correlated with fertility. — It is in the 
 highest degree desirable that the breeder should be able 
 to distinguish those qualities, external and internal, 
 which are in any way correlated either with fertility or 
 sterility. Unfortunately we cannot now speak with as- 
 surance on all the supposed evidences of fertility in 
 animals, but some characters are undoubtedly closely 
 correlated with fertility and we may through them learn 
 to judge of the probable existence or nonexistence of 
 this most desirable trait. Manifestly, characters closely 
 correlated with fertility will finally persist and become 
 dominant. It is equally evident that those characters 
 of the animal body which are correlated with infertility 
 will ultimately disappear. The skillful judge of breed- 
 ing animals recognizes some such correlation in the selec- 
 
FERTILITY 103 
 
 tion of both male and female individuals. The breeder 
 emphasizes the existence of those general qualities which 
 give to the male a distinctly masculine appearance and 
 to the female a clearly recognizable character of femininity. 
 The bull possessing a markedly masculine aspect is held 
 to be a '' good breeder." Whether it is meant by this 
 that such a bull is prepotent in fixing his own charac- 
 teristics upon his offspring or, what is more probable, 
 that a bull of this character is more than ordinarily effi- 
 cient in the development of sperm-cells, it is still true 
 that the masculine type may be regarded as in some 
 degree at least correlated with fertility. Supernumerary 
 mammae have been found in many cases associated with 
 exceptional fertility. In describing the dam of triplet 
 calves. Pearl ^ remarks : " It is of interest to note that 
 this cow has two very small posterior mammae. It is 
 of course impossible to say whether this occurrence of 
 supernumerary mammse is directly connected with the 
 high degree of fecundity exhibited by this cow, but this 
 may fairly be regarded as probably the case because of 
 the fact that these two things are known to be associated 
 in other forms." The sheep breeding experiments at 
 Beinn Bhreagh^ by Alexander Graham Bell have suggested 
 a possible correlation between extra nipples and unusual 
 fecundity. Stature and fertility have been found by 
 Pearson ^ to be somewhat closely correlated among women. 
 The taller women are on the average more fertile. If this 
 is generally true, the stature of women is likely to increase 
 at least until it has reached a point which satisfies the 
 correlation existing. Among swine-breeders it is generally 
 
 1 hoc. cit. 
 
 2 Bell, Science, N. S., vol. 36, pp. 378-384. 
 
 ^ Pearson, "Grammar of Science," pp. 441-445. 
 
104 THE BREEDING OF ANIMALS 
 
 believed that sows with rather long bodies are more fertile 
 than shorter, more compact individuals. It seems to be 
 true also that females having a somewhat loose and open 
 conformation are generally more certain breeders. 
 
 The milking function of animals is in a measure corre- 
 lated with the quality of fecundity. Breeds of animals 
 and individuals which have the milking function well 
 developed are more fecund than those in which the devel- 
 opment of this quality has been neglected. Tanner/ 
 in his interesting discussion on " The Reproductive 
 Powers of Animals," says : " The formation of milk is 
 intimately correlated with the reproductive powers. 
 The secretion of milk is dependent upon the activity of 
 the mammary glands and these are either under the direct 
 influence of the breeding organs or else they sympathize 
 very closely with them. Those animals which breed 
 with the least difficulty yield the best supplies of milk 
 and produce the most healthy and vigorous offspring." 
 He also adds that, " Since a short supply of milk is indica- 
 tive of and associated with enfeebled breeding powers 
 every care should be taken to obviate this defect." 
 
 It must be admitted that our knowledge on the sub- 
 ject of characters correlated with fertility is as yet frag- 
 mentary and indefinite. The importance of this quality 
 in practical breeding should make this a fruitful field 
 for further investigation. 
 
 102. In-breeding and fertility. — Continuous in-breed- 
 ing among domestic animals has in many instances been 
 followed by low fecundity or absolute sterility. It is 
 generally believed by practical breeders that of all the 
 ill effects supposed to result from in-breeding, lessened 
 
 ^Tanner, "The Reproductive Powers of Animals," Journal 
 of Royal Agricultural Society, 1865, p. 270. 
 
FERTILITY 105 
 
 fertility is the one most likely to follow. Whether this 
 loss of fecundity in animals of consanguineous breeding 
 is to be attributed to in-breeding per se or whether it is 
 due to the rapid fixing of a tendency to sterility already 
 existing in the family, it is nevertheless true that there 
 exists a certain amount of probability that continuous 
 close-breeding will ultimately affect injuriously the 
 fertility of animals. This question is discussed at some 
 length under " In-breeding/' Chapter XL 
 
 103. Cross-breeding and fertility. — It naturally fol- 
 lows that if in-breeding is unfavorable to full fecundity, 
 cross-breeding must tend to develop this desirable quality. 
 Here again it is not easy to trace the increased fertility 
 which follows the mating of animals of diverse characters 
 to the sole act of crossing. Many of the cases of increased 
 fecundity due to crossing may be explained on the basis 
 of introducing the new quality of high fertility. If fertil- 
 ity is a dominant character transmitted in accordance 
 with the Mendelian principle of dominance, it is easy to 
 understand why the cross-bred animal may exhibit, as 
 it often does, a greater degree of fecundity than can be 
 accounted for on the assumption of blended inheritance 
 of this quality from both parents. What actually happens 
 is that one of the parents possesses the quality of fertility 
 in high degree and this becomes dominant in the offspring. 
 A certain proportion of the offspring, therefore, receive 
 in the constitution of the germ-plasm all- the high fertility 
 which is an inherent part of the germ substance of the one 
 parent. It should also follow that a certain proportion of 
 the offspring inherit unchanged the tendency to low fecun- 
 dity characteristic of the other parent. It must be ad- 
 mitted that evidences of the latter are still lacking, but it 
 should be possible by experiment to determine this point. 
 
106 THE BREEDING OF ANIMALS 
 
 104. Unusual fertility. — Each species and most varie- 
 ties or breeds of animals have a fairly uniform and normal 
 rate of increase. Thus the normal number of young at a 
 birth in cattle and horses is one. It is also probably 
 true that among sheep one is the normal number of young 
 at each birth. But many breeds of sheep have been 
 so changed by domestication that twins are frequent 
 and triplets are not rare. The quality of fertility is 
 undoubtedly transmitted by heredity. It is therefore 
 possible to increase the normal fertility of the domestic 
 sheep by selection. Among cattle the production of 
 twins has not been regarded as a particularly desirable 
 quality, and hence no attempt has been made to increase 
 the normal birth number of the bovine species. It is 
 not difficult, however, to conceive that it would be com- 
 paratively easy to develop a breed or variety of cattle 
 which would produce twins. Cases of unusual fertility 
 among all classes of the domestic animals are frequent. 
 These are of enough importance from a practical point 
 of view and of sufficient biological significance to be given 
 a place in a discussion on fertility. 
 
 105. Unusual fertility among horses. — Exceptional 
 fertility among horses is generally to be found in connec- 
 tion with longevity and active and regular functioning 
 of the breeding powers rather than in unusual numbers 
 of young at a birth. A mare twenty-five years old, owned 
 by R. O'Heren of Illinois, in 1904 was suckling her twen- 
 tieth colt. She was one-half Thoroughbred and one-half 
 Clydesdale and was still strong and active.^ The Thor- 
 oughbred mare, Fanny Cook, dam of Daniel Lambert, 
 produced fifteen foals and dropped twins at twenty-two 
 
 1 Reported in a letter to the author by R. H. Dunn, Illiopolis, 
 111. 
 
 i 
 
FERTILITY 107 
 
 years of age. A Clydesdale mare belonging to G. W. 
 Henry of Burlington, Iowa, was the mother of nine- 
 teen foals and was supposed to be in foal again.^ Poca- 
 hontas, a running mare, was the mother of fifteen foals 
 and dropped her last ' at the time she was twenty-five 
 years of age. 
 
 106. Unusual fertility among cattle. — Some remark- 
 able cases of fecundity among cattle have been recorded. 
 In most cases the ability to ripen a number of eggs dur- 
 ing one period of heat seems to be inherent. A cow that 
 has produced twins or triplets is very apt to do so again. 
 This tendency to multiple gestation in cattle is well 
 illustrated by a family of cattle on a New Hampshire 
 farm reported by Wentworth.^ " The foundress of the 
 family was a grade Holstein cow, herself a twin, about 
 seven years old. She has been on the farm ever since 
 she was dropped and has given birth to seven calves. 
 Her first service was to a Guernsey bull and resulted in a 
 pair of yellow and white heifers, one of which is now in 
 the herd. Her second mating to a red Shorthorn bull 
 resulted in a single black and white bull calf that was 
 vealed. An Ayrshire bull sired her third calves, twin 
 black and white bulls, but neither of these was good 
 enough to raise. Her fourth service was to a Holstein 
 bull and from it she produced twin black and white heifers 
 that promise well as milkers." 
 
 "The yellow and white twin first produced by the 
 old cow is now four years old and has twice borne twins. 
 To an Ayrshire bull she produced a pair of yellow and 
 white bull calves that early went to the butcher and to a 
 
 1 Sanders, "Horse Breeding," p. 179. 
 
 2 Wentworth, E. N., " Twins in Three Generations," Breeder's 
 Gazette, vol. 62, p. 133. 
 
108 THE BREEDING OF ANIMALS 
 
 Holstein bull she gave birth to twin black and white 
 heifers last December." 
 
 Pearl ^ has described an interesting case of triplet 
 calves from a grade Guernsey cow seven years old. The 
 sire was a young grade Hereford bull which had not 
 shown any unusual tendency to sire twins or triplets. 
 Two of the .calves were heifers and had the typical white 
 face of the Hereford breed. The third calf, a bull, was 
 a typical Guernsey and in color and coat markings re- 
 sembled somewhat closely his dam. (Plate IV.) 
 
 In reference to the breeding record of these triplet 
 calves, Pearl says : " The writer asked Mr. Walter, 
 the owner of the calves here described, to pay particular 
 attention to the sexual behavior of these triplets. This 
 was done. As has already been implied in what has gone 
 before, the male individual of the triplets was entirely 
 functional sexually. He was used in service locally; 
 got good calves ; and apparently got as high a proportion 
 of calves as would be expected from a bull of his age. In 
 regard to the sexual history of the female individuals 
 of the triplets, Mr. Walter has the following to say in a 
 letter dated April 11, 1910. After noting the fact that 
 these two supposed heifers had been killed and sold in 
 the village market he says : ' Neither of them had 
 ever been in heat.' In earlier letters Mr. Walter on sev- 
 eral occasions said that these calves never showed the 
 slightest signs of being in heat. From the account given 
 by the butcher who killed these animals it appears prob- 
 able that in both individuals the conditions were such as 
 have been described for many free-martins. Neither 
 uterus or tubes were recognized, but the vagina apparently 
 
 » Pearl, "Triplet Calves," Bulletin 204, Maine Agricultural 
 Experiment Station. 
 
Plate IV. — Unusual fertility in the cow. 
 grade Guernsey dam and grade Hereford sire. 
 
 Triplet calves from a 
 
FERTILITY 109 
 
 ended at its anterior end as a blind sack. Although 
 detailed anatomical data are lacking, there can be 
 little doubt, I believe, because of both physiological 
 fact and absence of oestrus and the lack (?) or minute, 
 infantile condition of uterus and Fallopian tubes, that 
 these two supposed female individuals were really free- 
 martins." 
 
 The cow possessed two supernumerary mammae just 
 behind the posterior pair. The occurrence of super- 
 numerary mammae has before been observed to accom- 
 pany the tendency to multiple births. 
 
 A seven-year-old Shorthorn cow dropped seven dead 
 calves at one birth. They were sired by a Holstein bull.^ 
 A Shorthorn cow three years old, on post mortem, was 
 found to be carrying six perfectly developed calves in 
 her uterus.^ Another Shorthorn cow gave birth to four 
 calves, three of which were weak and undeveloped.^ A 
 cross-bred cow gave birth to seven calves within a period 
 of twelve months. All these calves w^ere born alive.^ 
 A cow dropped three pairs of twins in succession during 
 a period of two years.^ A grade Guernsey cow on a farm 
 in Washington County, Pennsylvania, gave birth to 
 triplets. This cow was ten years old and had produced 
 fifteen calves at eight births. A cow twenty-two years 
 old is reported as having had twenty calves and was 
 again pregnant.® A remarkable case of continued high 
 fertility in a cow is quoted by Pearl from McGillwray's 
 " Manual of Veterinary Science and Practice." The cow 
 
 1 Country Gentleman, 1895, p. 595. 
 
 2 Ibid., 1880, p. 313. 
 
 3 Ihid., 1891, p. 339. 
 
 4 Ibid., 1893, p. 231. 
 
 5 Breeder's Gazette, 1898, p. 7. 
 
 ^ Rural New-Yorker, 1906, December. 
 
110 
 
 THE BREEDING OF ANIMALS 
 
 described was of " the black polled breed " and her 
 record of births follows : 
 
 Year Number of Calves at Birth 
 
 1842 
 
 
 
 1 
 
 1843 
 
 
 
 3 
 
 1843 
 
 
 
 4 
 
 1844 
 
 
 
 2 
 
 1845 
 
 
 
 3 
 
 1846 
 
 
 
 6 
 
 1847 
 
 
 
 2 
 
 1848 
 
 
 
 4 
 
 Total 
 
 
 
 25 
 
 This the cow's first calf 
 
 All lived to adult age 
 
 One died. (Seven calves in one year) 
 
 Lived to maturity 
 
 Lived to maturity 
 
 All died prematurely 
 
 Came to maturity 
 
 Mean number per birth — 3.125 
 
 107. Unusual fertility among sheep. — Sheep normally 
 produce a larger proportion of twins than cattle or horses. 
 This may be due in a measure to the fact that the sheep 
 has a much shorter period of gestation. It is true in 
 general that those mammals having the shortest periods 
 of gestation are most prolific. Some remarkable cases 
 of great fertility among sheep are matters of record. 
 A three-year-old grade Cotswold ewe gave birth to five 
 fully developed lambs. Two died at birth, the others in 
 a few hours.^ A Horned Dorset ewe four years old 
 dropped five lambs at two births within a ten months' 
 period.^ A Radnor ewe dropped six lambs at one birth, 
 of which five lived and thrived.^ An Oxford-down ewe 
 gave birth to four strong, vigorous lambs which grew 
 rapidly and weighed one hundred and sixty-two pounds 
 at eight weeks old.^ A prolific ewe at one birth dropped 
 five lambs, all of which were perfectly developed and grew 
 rapidly.^ A Leicester ewe gave birth to six strong, healthy 
 
 1 Country Gentleman, 1893, p. 171. 
 
 2 Breeder's Gazette, 1894, p. 327. 
 
 ^ Country Gentleman, 1892, p. 331. 
 " Breeder's Gazette, 1893, p. 388. 
 ^ Country Gentleman, 1878, p. 329. 
 
FERTILITY 111 
 
 lambs, four of which the mother nursed successfully. 
 The earless Shanghai breed of sheep exhibited in the 
 London Zoological Gardens in 1857 seem to have inherited 
 a remarkable fecundity. Bartlett ^ has described this 
 variety as breeding twice each year and often producing 
 four or five at a birth. In the spring of 1857 three ewes 
 of this breed gave birth to thirteen lambs. 
 
 108. Unusual fertility among swine. — There is more 
 difficulty in determining the normal number of young at 
 a birth among swine than among other domestic animals. 
 There is considerable variation among individuals belong- 
 ing to the same breed and between different breeds. 
 Some particular cases of high fertility are described 
 below : 
 
 A three-year-old Chester White sow ^ farrowed ninety- 
 six pigs in six litters. There were fourteen in each of 
 the first three litters and eighteen in each of those last 
 farrowed. This tendency among highly fecund indi- 
 viduals to give birth to larger and larger numbers has 
 been observed in cattle, sheep and swine. 
 
 A Poland China sow ^ produced thirty-four living pigs 
 in three litters during a single twelve months' period. 
 
 A sow ^ gave birth to twenty-one pigs in a litter. Pre- 
 vious to this she had farrowed two litters of fifteen and 
 seventeen pigs each. A sow of uncertain breed ^ dropped 
 twenty-three pigs in one litter. All but two of these 
 were born alive. The same sow gave birth to eighty- 
 five pigs in five litters. Ray L. Zimmerman of Amazonia, 
 Andrew County, Missouri, reports to the author that a 
 
 1 Bartlett, Proc. Zool. Soc, London, 1857, p. 105. 
 
 2 Breeder's Gazette, 1897, p. 368. 
 
 3 Ibid., 1894, p. 308. 
 
 ^ Country Gentleman, 1887, p. 281. 
 5 Ibid., i894, p. 915. 
 
112 THE BREEDING OF ANIMALS 
 
 Poland China sow owned by W. Minner of that county 
 farrowed twenty-five pigs in one litter. 
 
 109. Unusual fertility among poultry. — An instance 
 of remarkable ability in egg-laying is given in the Experi- 
 ment Station Record, vol. 28, p. 270. In this volume is 
 described a Single Comb Brown Leghorn hen which laid 
 257 eggs in twelve months. This hen weighed only 
 three and two-tenths pounds. The average weight of 
 the eggs was one and eight-tenths ounces. At the Dela- 
 ware Experiment Station a White Leghorn hen, Lady 
 Eglantine, laid 314 eggs in one year. 
 
CHAPTER VI 
 STERILITY 
 
 It goes without saying that the first essential quaUty 
 in a breeding animal is the ability to produce young. 
 The more highly developed the animal is in those special 
 characters which have been fixed by selection, the more 
 important becomes the mere ability of an individual to 
 give birth to offspring. In an animal reared primarily 
 for commercial purposes, like the hog or the beef type, 
 the barren individual is not so serious a loss, as it may 
 still have a value for meat. 
 
 It is well known that many individuals among the 
 domestic animals are sterile. Such sterility is found 
 among animals reared under the best conditions, as well 
 as among those subjected to less skillful husbandry. 
 Barrenness occurs in individuals which are a part of 
 herds or flocks in which all animals are surrounded by 
 identically the same conditions. It must be true, there- 
 fore, that some animals possess a tendency to barrenness 
 in a more marked degree than others. This tendency 
 may possibly be inherited. Barrenness may be only 
 temporary or it may be a permanent condition. When it 
 is a temporary condition, it can often be alleviated by 
 knowing the conditions which are favorable to fertility, 
 and particularly those conditions which are known to act 
 unfavorably upon the breeding functions. 
 I 113 
 
114 THE BREEDING OF ANIMALS 
 
 110. The causes of sterility. — The various causes ^ 
 of sterility may be classified as anatomical, physiological, 
 pathological or psychological. Sterility in the male may 
 be due to an inability to perform the sexual act, which 
 condition is known as impotence, or it may be due to an 
 inability properly to develop spermatozoa. 
 
 111. Causes of sterility in the male. — The male may 
 be sterile as a result of undeveloped testicles as in some 
 ridglings, where the testicles are retained in the abdomen. 
 The ridgling is not always permanently sterile and may 
 be fully fertile, but the failure of the testicles to descend 
 normally from the abdominal cavity into the scrotum 
 is to be regarded with suspicion by the breeder. The 
 only way to determine whether a particular ridgling is 
 fertile is by actual trial. There is no medicinal or surgi- 
 cal treatment which can make a barren ridgling fertile. 
 
 Bulls, boars and stallions which are fed upon a generous 
 ration of highly nutritious food and are not given regular 
 exercise tend to become over-fat, and such a condition 
 often leads to fatty degeneration of the testicles and conse- 
 quent sterility. This condition is recognized by all suc- 
 cessful breeders. Breeding males that have proven 
 themselves of great merit as sires and are not intended 
 for exhibition are generally and wisely maintained on a 
 moderate allowance of nutritious food, being careful 
 to limit the amount and provide some means for exercise, 
 thus avoiding the almost inevitable fatty degeneration 
 of the reproductive tissues which follows long-continued 
 high feeding combined with little exercise. An example 
 of the intimate relation of these factors to fertility is to 
 be observed in the breeding practices of many modern 
 
 ^ See "Diseases of the Horse," U. S. Department of Agri- 
 culture, 1907, pp. 151-154. 
 
STERILITY 115 
 
 owners of draft stallions as compared with the methods 
 of early stallioners in the newer agricultural sections of 
 the United States. It was formerly the custom to drive 
 or ride the stallion from farm to farm, thus often covering 
 a territory of 100 to 200 square miles. Stallions so handled 
 were notoriously sure foal-getters and not infrequently 
 were successful in getting from eighty-five to ninety-five 
 per cent of the mares in foal. The modern plan of 
 keeping the draft stallion in high condition and stand- 
 ing him for service at one barn, thus requiring all mares 
 to come to him, has undoubtedly reduced the fertility 
 of draft stallions. It is no unusual event for k draft 
 stallion so managed to get only sixty per cent of mares in 
 foal, while seventy-five per cent of the mares in foal is 
 regarded by some stallioners as a fair average for stal- 
 lions handled in this manner. The fatty degeneration 
 of the vasa deferentia or excretory ducts of the tes- 
 ticles is also a not infrequent cause of sterility in very 
 fat animals. 
 
 Any injury or deformity of the penis which renders 
 the act of copulation painful or impossible is to be included 
 in the category of anatomical causes of sterility. In 
 this class may be included inflammation or ulceration 
 of the mucous membrane enclosing the penis, paralysis 
 of that organ, and the presence of tumors on the penis 
 itself or its appendages. Muscular and bone diseases 
 which in any way interfere with the exercise of the breed- 
 ing function are causes of barrenness. Spavin or ring 
 bone may cause the stallion such inconvenience and dis- 
 tress in mounting as to prevent copulation and thus indi- 
 rectly be a cause of barrenness. Similarly, diseases of the 
 muscles of the back and loins may be responsible for 
 sterility in certain individuals. Diseases of the brain 
 
116 THE BREEDING OF ANIMALS 
 
 and spinal cord, particularly those which control the 
 act of coition/ diabetes and albuminuria are to be regarded 
 as causes of sterility. 
 
 The potency of the semen of the male may be so weak- 
 ened by too frequent services by the stallion as to result 
 •in sterility. The number and frequency of services 
 which can be required of a stallion and still retain the 
 full vitality of the sperm-cells varies greatly with different 
 individuals. An interesting contribution to this subject 
 is reported by Lewis : ^ A draft stallion was permitted 
 one cover daily for nine consecutive days. Samples 
 of the semen were taken to the laboratory in a warm steri- 
 lized receptacle. The number of sperm-cells to the cubic 
 millimeter in the semen from the first service was 131,750. 
 The number of sperm-cells decreased daily with consider- 
 able uniformity until the ninth service, when the number 
 suddenly diminished from 51,480 to 5840. The vitality 
 of the spermatozoa was determined by maintaining the 
 fluid at a uniform temperature and determining the num- 
 ber of viable sperm-cells at the end of a given period. 
 Thus when the semen was kept at a temperature of 31 
 to 35° C. it was found that five per cent of the 
 cells from the first service were alive after nine and five- 
 tenths hours. From the third service no cells were alive 
 after six hours. From the sixth service no cells were 
 alive after four hours, and from the eighth service no cells 
 were alive after three hours. In a second test a grade 
 stallion was bred eleven times on consecutive days. 
 The author summarizing this test concludes that : ^ 
 " Approximately the vitality of the cells decreased one- 
 
 1 Comer, "Diseases of the Male Generative Organs, " 1907. 
 
 2 Lewis, Oklahoma Experiment Station, Bui. 96, 1911. 
 ^ See Marshall, "The Physiology of Reproduction." 
 
STERILITY 117 
 
 half and the number to one-fifth in the last or eleventh 
 service of the series as compared with the condition of 
 the semen at the first service." Other conditions which 
 are to be regarded as sources of barrenness are incomplete 
 erections, premature ejaculations, fear and repugnance. 
 The inability of the male to produce fertile semen may 
 be a congenital condition or it may be acquired through 
 some of the causes mentioned in this chapter. 
 
 112. Sterility in the female. — The failure of the 
 female to produce offspring is due to a variety of causes. 
 Some of these are inherent and cannot be successfully 
 treated. Such animals are permanently barren and of 
 course useless for breeding purposes. There are other 
 causes of infertility which are the result of purely tempo- 
 rary circumstances, and these may often yield to skillful 
 treatment by man and valuable animals thus become 
 regular breeders. Some of the more important causes 
 of sterility which are temporary and which may yield 
 to treatment are mentioned below. 
 
 113. Closure of the cervix. — Mares and cows often 
 fail to become pregnant as a result of the constriction of 
 the muscles forming the neck of the womb. This spas- 
 modic closure of the cervix prevents the passage of the 
 semen from the vagina into the uterus, and the fertiliza- 
 tion of the egg is thus prevented. This condition is more 
 frequent in young females that have never been pregnant, 
 but is not uncommon among animals that have previously 
 given birth to offspring. This condition may generally 
 be successfully treated by a simple operation known to 
 the stallioners as opening. The treatment for this con- 
 dition is admirably and clearly described by Law ^ as 
 follows : '' Spasmodic closure of the neck of the womb 
 
 ^ " Diseases of the Horse," U. S. Department of Agriculture, 1907. 
 
118 THE BREEDING OF ANIMALS 
 
 is common and is easily remedied in the mare by dilata- 
 tion with the fingers. The hand, smeared with bella- 
 donna ointment and with the fingers drawn into the form 
 of a cone, is introduced through the vagina until the pro- 
 jecting, rounded neck of the womb is felt at its anterior 
 end. This is opened by the careful insertion of one finger 
 at a time, until the fingers have been passed through the 
 constricted neck into the open cavity of the womb. The 
 introduction is made with a gentle rotary motion, and 
 all precipitate violence is avoided, as abrasion, laceration 
 or other cause of irritation is likely to interfere with 
 the retention of the semen and with impregnation. If 
 the neck of the womb is rigid and unyielding from the 
 induration which follows inflammation — a rare condi- 
 tion in the mare, though common in the cow — more 
 force will be requisite, and it may even be needful to incise 
 the neck to the depth of one-sixth of an inch in four 
 or more opposite directions prior to forcible dilation. The 
 incision may be made with a probe-pointed knife, and 
 should be done by a professional man if possible. The 
 subsequent dilatation may be best effected by the slow 
 expansion of sponge or seaweed tents inserted into the 
 narrow canal. In such cases it is best to let the wounds 
 of the neck heal before putting to horse." 
 
 114. Obstruction of Fallopian tubes resulting from 
 excessive fatness. — In excessively fat animals, the 
 Fallopian tubes may become mechanically obstructed 
 by the pressure of fat tissue. This closure of the tube 
 makes it impossible for the ova to descend into the uterus, 
 and although the female may come regularly in heat and 
 coition occur, the animal does not become pregnant. 
 This condition does not necessarily involve fatty degen- 
 eration of the reproductive tissues, but may be associated 
 
Plate V. — Normal healthy uterus of sow. a, ovary ; h, fimbriated 
 end of Fallopian tube ; c, central part of Fallopian tube ; d, junction of 
 Fallopian tube with horn of uterus ; e, uterine folds of the horns of uterus ; 
 /, body of uterus; o, position of *'os uteri"; vag., vagina vulva, bladder. 
 
Plate VI. — Sterility in the sow. Generative organs of a domestic 
 sow, illustrating cystic ovaries which in this case resulted in complete 
 sterility. 
 
STERILITY 119 
 
 with it. It is of course not possible to determine by 
 external examination of the live animal whether failure 
 to breed in a particular case is due to mechanical obstruc- 
 tion of the Fallopian tubes or to other causes. It is often 
 possible to overcome this difficulty by dieting the animal. 
 Very fat animals which do not breed should be placed 
 upon a restricted diet which will cause them to lose weight 
 regularly until they have regained a normal breeding 
 condition. 
 
 115. Other causes of barrenness. — Other conditions 
 which may be regarded as more or less temporary causes 
 of barrenness are : (a) insufficient food supply, causing 
 emaciation and a consequent failure of the sexual organs 
 to mature ova; (6) failure of the animal to retain the 
 semen of the male, due to unusual nervous irritability 
 of the female sexual organs ; and (c) sudden and marked 
 change of condition, such as is brought about by the 
 transportation of animals from one continent to an- 
 other. (Plates V and VI.) 
 
 Some of the causes and treatment of sterility have 
 already been somewhat fully discussed under the general 
 subject of fertility. A mere mention of some of the 
 above causes of sterility indicates the treatment. In 
 many cases of sterility all that is needed is to remove 
 the cause. The nervous irritability of the female sexual 
 organs seems to be caused by, or at least associated with, 
 an unusual flow of blood to the generative organs, causing 
 congestion. This condition can be alleviated sometimes 
 by exercising the female even to the point of exhaustion. 
 It is a well-known fact that the Arabs were in the habit 
 of riding their mares to exhaustion just before mating 
 with the stallion. This treatment brought about a 
 generally relaxed condition of the whole body and par- 
 
120 THE BREEDING OF ANIMALS 
 
 ticularly of the reproductive organs, which is to be re- 
 garded as favorable for conception. 
 
 The importation of animals from foreign countries 
 often results in temporary barrenness. This condition 
 seldom or never becomes permanent. 
 
 116. Sterility from fatty degeneration. — The main- 
 taining of animals in an excessively fat condition for a 
 long period of time will eventually result in fatty degener- 
 ation of the tissues. When this condition attacks the 
 ovaries, it frequently causes permanent sterility. Cer- 
 tain foods are believed to hasten fatty degeneration of the 
 reproductive tissues. Tanner ^ holds that " this fatty 
 degeneration of the ovaries has been traced to the use of 
 foods rich in sugar. I have reason to believe that the 
 action of sugar in its various forms is most important 
 in its influence upon the generative system, and I think 
 there is just cause for considering that any animal may 
 by its use be rendered incompetent for propagating its 
 species." 
 
 117. Sterility caused by abortion. — Among the impor- 
 tant causes of infertility among the domestic animals 
 probably none is responsible for so many failures to 
 produce living offspring as abortion. Two kinds of 
 abortion are recognized, non-contagious and contagious. 
 Non-contagious abortion may result from a variety of 
 causes closely associated with the environment of the 
 animal. Law ^ gives a number of the more important 
 causes of abortion in the mare. " The mare may abort 
 by reason of almost any cause that very profoundly dis- 
 
 ^ Tanner, "The Reproductive Powers of the Domestic Ani- 
 mals," Journal of the Royal Agricultural Society, vol. 1, 1865, 
 p. 267. 
 
 2 Law, "Diseases of the Horse," U. S. Department of Agri- 
 culture, 1903. 
 
STERILITY 121 
 
 turbs the system. Hence very violent inflammations 
 of important internal organs (bowels, kidneys, bladder, 
 lungs) may induce abortion. Profuse diarrhea, whether 
 occurring from the reckless use of purgatives, the con- 
 sumption of irritants in the food, or a simple indigestion 
 is an effective cause. No less so is acute indigestion 
 with evolution of gas in the intestines (bloating). The 
 presence of stone in the kidneys, uterus, bladder or urethra 
 may induce so much sympathetic disorder in the w^omb 
 as to induce abortion. In exceptional cases wherein 
 mares come in heat during gestation, service by the 
 stallion may cause abortion. Blows or pressure on the 
 abdomen, rapid driving or riding of the pregnant mare, 
 especially if she is soft and out of condition from idleness, 
 the brutal use of the spur or whip, and the jolting and 
 straining of travel by rail or boat are prolific causes. 
 Bleeding the pregnant mare, a painful surgical opera- 
 tion, and the throwing and constraint resorted to for an 
 operation are other causes. Traveling on heavy muddy 
 roads, slips and falls on ice, and jumping must be added. 
 "The stimulation of the abdominal organs by a full drink 
 of iced water may precipitate a miscarriage, as may expo- 
 sure to a cold rainstorm or a very cold night after a warm 
 day. Irritant poisons that act on the urinary or genera- 
 tive organs, such as Spanish flies, rue, savin, tansy, cotton- 
 root bark, ergot of rye or other grasses, the smut of 
 maize and other grain, and various fungi in musty fodder 
 are additional causes. Frosted food, indigestible food 
 and, above all, green succulent vegetables in a frozen 
 state, have proved effective factors, and filthy stagnant 
 water is dangerous. Low condition in the dam and 
 plethora have in opposite ways caused abortion, and hot, 
 relaxing stables and lack of exercise strongly induce it. 
 
122 THE BREEDING OF ANIMALS 
 
 The exhaustion of the sire by too frequent service, entail- 
 ing debility of the offspring and disease of the fetus or of its 
 envelopes, must be recognized as a further cause." The 
 symptoms of abortion are similar to those of approach- 
 ing parturition (see p. 75), if the threatened abortion 
 occurs during the later stages of pregnancy. Abortion 
 may occur during the first four weeks of pregnancy with- 
 out any very marked symptoms. The fact of abortion 
 is indicated by the animal again coming in heat. But, 
 as already shown in cases of superfoetation, the occurrence 
 of heat is not absolute evidence that abortion has resulted. 
 Ewart ^ has called attention to the fact that the mare 
 is far more apt to abort at certain stages of gestation 
 than at others. He regards the period from the sixth 
 to the ninth week as one during which the mare is pecul- 
 iarly susceptible to changes in her environment which 
 may have a tendency to cause abortion. This is due 
 to a change in the form of attachment of the foetus to the 
 uterus, from the primitive yolk sac to the more permanent 
 villi. " At the end of the third week of gestation, when 
 the reproductive system passes through one of its periods 
 of general excitement, about one-fourth of the embryonic 
 sac probably adheres to the uterus ; but at the end of the 
 sixth week, when another wave of disturbance arrives, 
 all the grappling structures are at one pole. Hence, 
 there is probably more chance of the embryo ' slipping ' 
 at the end of the sixth than at the end of the third week. 
 About the end of the seventh week the supply of nourish- 
 ment by means of the yolk sac is coming to an end, and 
 there is, perhaps, still about this time an hereditary tend- 
 ency for the embryo to escape. Unless the new and more 
 permanent nutritive apparatus is provided, unless a 
 
 1 Ewart, quoted by Marshall, loc. cit., p. 615. 
 
STERILITY 123 
 
 countless number of villi rapidly sprout out from the 
 allantois, the embryo will die from starvation during 
 the eighth week, and in a few days be discharged. It 
 may, therefore, be taken for granted that there is a cer- 
 tain amount of danger at the end of the third and sixth 
 weeks, but that the most critical period is about the end 
 of the seventh or beginning of the eighth week ; for unless 
 the villi appear in time, and succeed in coming into suffi- 
 ciently intimate relation with the uterine vessels, the 
 developmental process is of necessity forever arrested." 
 
 Abortion among sheep seems to be largely due to debili- 
 tating conditions due to insufficient and unsuitable food, 
 although Heape ^ has pointed out that shearling ewes 
 are more apt to abort than those of maturer age. 
 
 118. Contagious abortion and sterility. — The most 
 insidious, widespread and generally important cause of 
 sterility, especially among cows, is due to a germ infection 
 (Bad. abortus) which is recognized under the terms con- 
 tagious or infectious abortion. It is found oftener in 
 herds of dairy cattle than among beef breeds, not because 
 dairy animals are more susceptible to this disease, but 
 because they are generally handled in such a manner as 
 to provide more favorable conditions for its spread. 
 Beef breeds are generally less closely housed and they 
 are more frequently permitted to calve on the pastures, 
 thus avoiding two common circumstances favorable for 
 the transmission of the disease. The infection is carried 
 chiefly by the bull. If a healthy bull is permitted to 
 serve a cow infected with the germ of abortion, he will 
 generally transfer the infection to all cows which later 
 may be served by him. The disease is not communicated 
 to any important extent from cow to cow by merely 
 
 1 Heape, "Abortion, Barrenness and Fertility in Sheep." 
 
124 THE BREEDING OF ANIMALS 
 
 standing side by side in the same barn. The Scottish 
 Committee appointed to investigate abortion found that 
 infection might be carried from a diseased cow to a healthy 
 animal by inserting a small wad of cotton into the vagina 
 of a diseased cow for twenty minutes and transferring 
 this to the vagina of a healthy pregnant cow or sheep. 
 Such infection invariably caused abortion within a month.^ 
 The specific organism Bacterium abortus is probably not 
 the only germ which may cause abortion. MacFadyean ^ 
 has called attention to the very great increase in the 
 sterility of cows in Prussia and Switzerland during recent 
 years. The cause of this sterility has been ascribed to a 
 disease known as '' infectious granular vaginitis." This 
 affection produces an acute inflammation of the vulva 
 and vagina and the infection is spread through a herd 
 by the bull. Law ^ holds " that any micro-organism 
 which can live in or on the living membrane of the womb 
 producing a catarrhal inflammation, and which can be 
 transferred from animal to animal without losing its 
 vitality or potency is of necessity a cause of contagious 
 abortion." 
 
 119. Treatment for contagious abortion. — The con- 
 tinuance of contagious abortion is generally prolonged 
 even under the best of circumstances. Treatment may 
 sometimes be very successful, and again any form of treat- 
 ment may fail to make any lasting impression upon the 
 disease. As the bull is the chief source of contagion, the 
 treatment should start with him. Veterinarians recom- 
 mend that the sheath and external genitals of the bull 
 
 1 Law, "Diseases of Cattle," U. S. Department of Agriculture, 
 1908. 
 
 2 MacFadyean, Journal of the Royal Agricultural Society^ 
 1909, p. 337. 
 
 ^ Law, loc. ciL, p. 166. 
 
STERILITY 125 
 
 be thoroughly disinfected with a sohition of bichloride 
 of mercury 1 to 2000 containing one per cent of copper 
 sulfate. The same disinfectant should be used to flush 
 the vagina of the suspected cows. Nocard ^ recommends 
 the following solution for cleansing the external genitals, 
 anus and tail of the aborting cow : 
 
 Distilled or pure rain water .... 2 gallons 
 
 Hydrochloric acid 2\ ounces 
 
 Corrosive sublimate 2\ drachms 
 
 These ingredients should be thoroughly mixed. 
 
 In Denmark, according to Dalrymple,^ all membranes 
 and the foetus are buried in lime and the internal genital 
 organs of the cow are thoroughly disinfected with a one 
 per cent solution of creolin or a half per cent solution of 
 lysol. The external genitals of the bull and of cows about 
 to be bred are treated with the same solution. 
 
 All aborted tissues must be burned and the premises 
 thoroughly disinfected. This treatment is uncertain 
 and often unsuccessful. A breeder will generally gain 
 time in the eradication of abortion from his herd by insist- 
 ing upon never using a contaminated male on young heifers 
 bred for the first time or upon cows known to be free from 
 the disease. All infected and aborting cow^s should be 
 separated absolutely from the females w^hich have never 
 aborted. All cows known to be free from the disease 
 should be covered by a bull also known to be free from 
 infection. The uninfected herd must be guarded from 
 infection from the diseased herd. This plan will even- 
 tually build up a clean herd and no other method so far 
 devised is certain to accomplish this desirable result. 
 
 ^ Dalrymple, "Veterinary Obstetrics," p. 59. 
 2 Loc. cit. 
 
126 THE BREEDING OF ANIMALS 
 
 The problem, of treating the bull and cows known to 
 be infected is quite distinct from the building up of a 
 clean herd. Fortunately this infection is not transmitted 
 by heredity and is not necessarily spread from mother 
 to offspring by direct infection. It is, therefore, possible 
 for a breeder to retain in the young animals from the 
 infected herd the best products of his skill and experi- 
 ence. When a cow from the infected herd aborts, all 
 tissues expelled from the uterus should be promptly 
 burned and the stall thoroughly disinfected by a generous 
 use of lime. The vagina of the cow should be disinfected 
 with the solution described on p. 125. The aborting 
 cow should be permitted to rest at least six months before 
 breeding again. The prevention of abortion in a cow 
 already pregnant has been successfully accomplished in a 
 number of instances by internal applications of carbolic 
 acid. Taylor's^ successful experiments in preventing 
 impending abortion are worthy of note. A description 
 of the treatment of one cow is typical and will serve as 
 an example of the methods which w^ere generally successful. 
 A grade cow four years old that had aborted the previous 
 year and was known to be infected with granular vaginitis 
 was given the following treatment : At the beginning 
 of the fourth month of the period of gestation she was 
 given 200 cubic centimeters of a four per cent solution 
 of carbolic acid in her feed. The dose was increased to 
 250 cubic centimeters the fifth month and to 300, 350 and 
 400 cubic centimeters for the sixth, seventh and eighth 
 months respectively. This cow dropped a strong healthy 
 calf at the end of the normal period of gestation. A sum- 
 mary of the results in one herd treated by Taylor shows 
 
 ^ Taylor, Montana Experiment Station, Bulletin No. 90, 
 1912. 
 
STERILITY 127 
 
 that in 1908 there were fifteen per cent abortions, in 1909 
 twenty-five per cent, in 1910 five per cent, and in 1911 
 two-and-one-half per cent of abortions. The carboHc 
 treatment was begun in December, 1909. It is recom- 
 mended that infected males be treated in the same manner.^ 
 
 120. Diagnosis of contagious abortion. — This disease 
 is so widespread and causes such serious consequences 
 when once well established in a herd that it is often of 
 the greatest importance to be able to detect its presence 
 in animals, even those which are not at the time pregnant. 
 Various attempts have been made with greater or less 
 success to secure a reliable diagnostic agent which would 
 make it possible for the breeder to know which animals 
 in his herd are infected with the germ of contagious abor- 
 tion and thus be able to separate the infected individuals 
 from those which are healthy. 
 
 The first substance of this character to be used was 
 similar to tuberculin and mallein. The name of '' abor- 
 tin " was given to this substance by MacFadyean and 
 Stockman. This material was to be injected into the 
 circulation of the cows of a herd. The infected cows 
 showed a considerable rise in temperature following the 
 infection. The healthy cows showed but little or no 
 increase in temperature. BrtilP at Vienna, after testing 
 this method on a large number of cows, concluded that 
 abortin was an unreliable diagnostic agent for determining 
 the presence of contagious abortion in cattle. Other 
 investigators have reported similar unfavorable results 
 from the use of this material. 
 
 ^ See also Good, Kentucky Experiment Station, Bui. No. 165 ; 
 Surface, Kentucky Experiment Station, Bui. No. 166 ; MacNeal 
 and H. W. Mumford, Illinois Experiment Station, Bui. No. 152. 
 
 ^Bnill, "Berl. Tierartzt Woch.," Bd. 27, pp. 721-727. 
 
128 THE BREEDING OF ANIMALS 
 
 In cases of typhoid fever, the so-called agglutination 
 test was found to be a fairly reliable agent for the diagnosis 
 of this disease. In 1907-8, Ginstead in Denmark applied 
 this test successfully to cows suffering from contagious 
 abortion. Later MacFadyean and Stockman ^ published 
 the results of a limited number of investigations, report- 
 ing unfavorably upon this method. Later Holth and 
 Wall,^ after an extensive series of investigations involving 
 hundreds of cows, concluded that the agglutination test 
 was a reliable diagnostic agent but probably subject to 
 larger error than the complement fixation test. 
 
 121. The complement fixation test.^ — Neither the 
 abortin nor the agglutination test has proven entirely 
 satisfactory under all circumstances. The most reliable 
 test now available is the complement fixation test.^ 
 Connaway of the Missouri Experiment Station says, 
 " This test has been found very reliable as a diagnostic 
 method in contagious abortion. The result of the test 
 on some infected herds shows that in old infected herds 
 the per cent of re-acting animals runs from 60 to 90 per 
 cent." This is a highly complicated and difficult test 
 to make, but will with practical certainty cause a reaction 
 in cows that have been infected. Cows that have aborted 
 may develop an immunity to this disease, and when this 
 has occurred the complement fixation test cannot be 
 used to distinguish between those cows which will abort 
 
 1 MacFadyean and Stockman, "Report of the Departmental 
 Committee to inquire into Epizootic Abortion," Pt. I, and 
 Appendix, London, 1909. 
 
 2 "Berl. Tierartzt Woch.," Bd., pp. 686-688, 1909. 
 
 ^See Surface, Kentucky Exp. Sta. Bui. No. 166; MacNeal 
 and Mumfoi^d, Illinois Exp. Sta. Bui. No. 152 ; Russell, Science, 
 N. S., vol. 34, p. 494, 1911; Wisconsin Research, Bui. No. 24, 
 1912. 
 
 ^ Missouri Experiment Station, Bui. 131, p. 486. 
 
STERILITY 129 
 
 and those which are immune. The great value of this 
 lies in the fact that the aborting cows may be entirely 
 separated from the healthy members and eventually 
 by this separation the disease may be entirely eliminated 
 from the herd. 
 
 122. Sterility of free-martins. — The birth of twins 
 among cattle is frequent. When a cow gives birth to 
 twins, one a female and the other a male, the female is 
 called a free-martin and is generally sterile. So far as 
 known, this condition does not exist among any other 
 known species of animal. Among sheep, for example, 
 where twins are very common, the female twin born with 
 a male may be even more fertile than the single born 
 lamb. No case of sterility among human twins has ever 
 been recorded where the sterile condition w^as believed 
 to be due to the fact that one twin was a male and the 
 other a female. Among cattle where both twins are of 
 the same sex both are fully fertile. This is, therefore, 
 a remarkable biological fact which it is difficult to explain. 
 Morse ^ reports that Dr. Luer found 113 cases of twins, 
 one a male and the other a female, in the records of the 
 East Prussian Holland Herd Book. Of this number all 
 the females were sterile except six. 
 
 The author has examined a considerable number of 
 free-martins and in every case of sterility the female 
 reproductive organs have been imperfectly developed. 
 One case examined is typical. A grade Aberdeen Angus 
 had every external appearance of a female. The loca- 
 tion and form of the external genital organs was that of 
 a true female. There were only two peculiarities which 
 were visible externally. A tuft of long hair resembling 
 the growth on the sheath of the bull grew from the lower 
 
 1 Morse, Breeder's Gazette, vol. 64, p. 346. 
 
 K 
 
130 THE BREEDING OF ANIMALS 
 
 extremity of the vulva. The mammary glands were 
 very small and but little developed and resembled more 
 the rudimentary mammary glands of a bull than the 
 normal glands of a cow. At two years of age this sup- 
 posed cow had never come in heat. She was permitted 
 to run in the same paddock with two mature bulls for a 
 period of six months, but never came in heat. This 
 animal was slaughtered and the reproductive organs 
 removed for examination. It was found that the animal 
 had a vulva and a very short vagina-like organ ending 
 in a blind sac. No uterus, Fallopian tubes or ovaries 
 were found. There was also found a rudimentary penis. 
 It seems probable that sterile free-martins are imperfect 
 males or hermaphrodites. It is not possible at this time 
 to give any satisfactory explanation of why there should 
 exist a greater tendency to hermaphroditism when twins 
 of different sex are born than twins of identical sex. It 
 is still more difficult to explain why this phenomenon 
 should occur exclusively among cattle. It is possible 
 that the explanation o£ this phenomenon is associated in 
 some way with the production of identical twins, but 
 this does not offer any satisfactory explanation of why 
 this strange occurrence should be found in the bovine 
 species alone. 
 
CHAPTER VII 
 HEREDITY 
 
 The characteristics of the individual are determined 
 by heredity and development. What an animal may 
 become, depends on the heritage received from its 
 ancestors. No organic being can be developed beyond 
 the limits imposed upon it by its inheritance. A favor- 
 able environment and good training will permit the 
 individual to achieve the full limit of its possibilities, 
 but no amount of training and no combination of favor- 
 able circumstances can ever lift the individual above the 
 inheritance which it has gained through its parents. 
 The trotting horse may have inherited the capacity to 
 trot a mile in two minutes, but if its development has 
 been arrested by insufficient food and an unfavorable 
 climate, and no attempt has been made to develop its 
 inherent ability to go fast, it can never achieve the full 
 measure of its possibilities. It is also true that if a horse 
 has not inherited from a line of trotting ancestors the 
 ability to go fast at the trot, no amount of training and 
 no system of feeding can develop the animal to a point 
 where it will be able to trot a mile in two minutes. 
 
 Heredity then represents what an animal really is or 
 can become. The individual cannot in any manner or 
 to any extent influence its own heredity. An animal's 
 inheritance is determined by its ancestors. The indi- 
 
 131 
 
132 THE BREEDING OF ANIMALS 
 
 vidual may profoundly Influence its development through 
 seeking a favorable environment and through habitual 
 use or disuse of its inherited tendencies. 
 
 123. Development. — The full realization of the in- 
 herited capacities of an animal is accomplished through 
 its environment and training. The most important 
 factors concerned in the environment of an animal are 
 food and climate, and these acting upon the inherited 
 qualities of the animal may profoundly influence the 
 actual characteristics of the individual. In order that 
 the inherent characteristics of any organic being may 
 attain to full development, a sufficient supply of food 
 must be available. When food is scarce, the individual 
 may be unable to develop, and what it may ultimately 
 become, may be greatly influenced by this lack of 
 food. A full and sufficient food supply may cause the 
 individual to develop beyond the average condition of 
 the species, particularly if the average environment does 
 not furnish a generous supply of food. 
 
 The training of the individual, likewise, is an important 
 factor in determining its ultimate development. Any 
 function of an animal which is not exercised may retro- 
 grade or in some cases practically disappear. The 
 milking function in domestic cattle is a good example of 
 the influence of both development and exercise or train- 
 ing. The highly developed dairy breeds of cattle, when 
 generously fed and carefully milked, produce very much 
 more milk than their wild ancestors. Individual cows 
 of modern dairy breeds, if starved and carelessly milked 
 or neglected, will fail to develop the highly specialized 
 milking function. 
 
 124. Heredity defined. — In much of the literature 
 of biology pertaining to heredity, there is a lack of definite- 
 
HEREDITY 133 
 
 ness in the use of terms. The Kterature of animal-breed- 
 ing is still less exact in its terminology. It seems impor- 
 tant, therefore, that in the very beginning we should have 
 as clear a conception as possible of the definitions of 
 heredity which have been proposed. Heredity is the 
 organic relation existing between an individual and its 
 ancestors. It is the continuous biological thread connect- 
 ing generations of organic beings. Heredity is '' organic 
 resemblance based on descent." ^ Thomson ^ has defined 
 heredity as " the organic or genetic relation between 
 successive generations." " Understood in its entirety," 
 says Herbert Spencer,^ " the law is that each plant or 
 animal, if it reproduces, gives origin to others like itself; 
 the likeness consisting, not so much in the repetition of 
 individual traits as in the assumption of the same general 
 structure." '' The transference of similar characters 
 from one generation of organisms to another, a process 
 effected by means of the germ-cells or gametes." ^ '' By 
 inheritance," says Lock,^ '' we mean those methods and 
 processes by which the constitution and characteristics 
 of an animal or plant are handed on to its offspring, this 
 transmission of characters being, of course, associated 
 with the fact that the offspring is developed by the pro- 
 cesses of growth out of a small fragment detached from 
 the parent organism." Another definition of heredity 
 is that it is the tendency of the offspring to be like the 
 parents. There exists a definite organic resemblance or 
 
 ^ Castle, " Heredity in Relation to Evolution and Animal 
 Breeding." 
 
 2 Thomson, "Heredity" (1908), p. 13. 
 
 ^Herbert Spencer, " Principles of Biology," vol. I, p. 301. 
 
 "* R. H. Lock, " Recent Progress in the Study of Variation, 
 Heredity and Evolution," 1906, p. 292. 
 
 ^ Loc. ciL, p. 1. 
 
134 THE BREEDING OF ANIMALS 
 
 relation between parents and offspring. This relation is 
 a universal biological phenomenon and is called heredity. 
 There exists a continuous line of descent from generation 
 to generation. The mechanism of heredity is to be found 
 in the protoplasm of the germ-cells. The stream of 
 descent is from germ-cell to germ-cell. The soma- or 
 body-cells constitute in a sense only a temporary abiding 
 place for the germ-plasm. 
 
 125. Heredity and variation not antagonistic. — It is 
 not stating the facts correctly to maintain that the tend- 
 ency of offspring to be like the parent, which we call 
 heredity, is opposed by the universal tendency of organ- 
 isms to vary. These are but two phases of the same 
 phenomenon. " Living beings do not exhibit unity 
 and diversity," says Brooks, "but unity in diversity. 
 These are not two facts but one. The fact is the indi- 
 viduality in kinship of living beings. Inheritance and 
 variation are not two things but two imperfect views 
 of a single process." There is a sense, of course, in which 
 variation is opposed to heredity. It is conceivable that 
 recombinations of characters may occur in the germinal 
 substance, and these new combinations may cause such 
 modification of characters already present that the new 
 organism may be radically changed. 
 
 Heredity is the genetic relation of parents and offspring. 
 On the average the offspring will be like the parents. 
 But this relation admits of variations within more or less 
 definitely prescribed limits. The offspring have an 
 individuality all their own, but this does not preclude the 
 existence of a genetic continuity which is the common 
 heritage of parents and offspring. 
 
 126. The kinds of heredity. — Every individual is 
 the result of a union of the germ-plasm of two individuals. 
 
HEREDITY 135 
 
 The evidences of this dual origin are not always exhibited 
 in the same manner. In some individual offspring the 
 characters of one parent may predominate, in others 
 the parental characters seem to blend so successfully 
 that often the child differs from either parent, while in 
 still others the characters of both parents appear in the 
 offspring with apparently equal force but, instead of blend- 
 ing, the characteristics of the parents appear clearly as 
 distinct and easily recognizable qualities. These methods 
 of transmission wxre called by Galton, blending, alternate 
 and particulate inheritance. 
 
 127. Blending inheritance. — In this type of inherit- 
 ance the characters of the offspring represent a blending 
 or intermingling of the characters of the two parents. 
 Stature in man may and often does represent the blend- 
 ing of the statures of the two parents. The stature of 
 the son or daughter is taller than the shorter parent, but 
 falls short of that of the taller parent. When a rela- 
 tively small mare is mated with a heavy draft stallion, 
 the resulting offspring is never so large as the sire nor so 
 small as the dam, but represents an approach to a mean 
 between the two. Another example of blended in- 
 heritance is to be observed in the cross-bred lambs 
 resulting from the union of a sire of the coarse wool type 
 and a dam belonging to the fine wool or Merino breed. 
 The lambs of such a cross are covered with wool which in 
 respect to density, length of staple and fineness of fiber 
 represents a blending of the characters of the parents. 
 
 In some cases of supposed blending inheritance, the 
 characters have been observed to follow the law of domi- 
 nance and segregation discovered by Mendel. 
 
 128. Alternative inheritance. — A charact«er may be 
 transmitted intact from one parent directly to the off- 
 
136 . THE BREEDING OF ANIMALS 
 
 spring without apparent modification by the other parent. 
 In this type of inheritance one parent seems to possess a 
 predominating influence in determining the characteristics 
 of the offspring. Many examples of this type of heredity 
 are to be observed among the domestic animals. The 
 white face of the Hereford breed of cattle is invariably 
 transmitted, even when one parent belongs to a widely 
 different breed. The quality of speed in horses is un- 
 doubtedly transmitted, sometimes in accordance with 
 Galton's alternative inheritance. Fecundity in the do- 
 mestic fowl has been shown by Pearl to be transmitted 
 through the male. The hen inherits fecundity directly 
 from the sire. The ability to lay a large number of eggs 
 is not transmitted from the mother to the immediate 
 female offspring, but to her male offspring. 
 
 " Hence if the daughters of high producing hens are 
 selected, one does not get in them the high productiveness 
 of the mother. It is her sons that inherit the character, 
 although they cannot show it except in their offspring." ^ 
 
 129. Particulate or mosaic inheritance. — The char- 
 acters of the parents are often transmitted in such a 
 manner that they are not in any sense blended but appear 
 rather as a mosaic. The color character is frequently 
 inherited as a mosaic. A very good example of this 
 kind of inheritance is seen in the Holstein Friesian breed 
 of cattle. This breed is black and white, these colors 
 appearing in definite, clearly defined areas and not blend- 
 ing. The Holstein Friesian breed was originated by 
 crossing a black breed and a white breed of cattle. The 
 colors black and white in other animals seem to behave 
 in a similar manner. When white hogs are mated with 
 black, the -offspring are always spotted. Recently it 
 
 1 Morgan, "Heredity and Sex," p. 213. 
 
HEREDITY 137 
 
 has been suggested that particulate inheritance is in 
 reahty true alternative inheritance in which the mosaic 
 result is caused by the absence of the factor for uniform- 
 
 130. Mendelian inheritance. — Progress in the investi- 
 gation of breeding problems has come through statistical 
 investigations, by cytological studies of the germ-cells 
 themselves, and by experimental breeding. Each of 
 these methods has contributed evidence of value in the 
 direction of a more definite understanding of the prin- 
 ciples of heredity. In recent years experimental breeding 
 has contributed very materially to our knowledge of 
 the science of heredity. Improvements in the technique 
 of cell studies has supplemented the results obtained by 
 experimental breeding. It is a significant fact that the 
 hypotheses based upon experimental breeding agree in 
 many important particulars with those derived from 
 minute investigations of the origin and development of 
 the germ-cells. 
 
 Perhaps the most remarkable series of investigations 
 in experimental breeding were those carried on by Johann 
 Gregor Mendel, an Austrian monk. These interesting 
 investigations gave a new impetus to the study of theoreti- 
 cal heredity and particularly to the practical improve- 
 ment of plants and animals. The investigations of Mendel 
 were first published in 1865 and over twenty years later 
 were again published in the Transactions of the Natural 
 History Society of Briinn. No attention was given to this 
 important contribution to the science of breeding, and 
 even Nageli, a former teacher of Mendel, to whom the 
 results were submitted, failed to recognize their funda- 
 mental significance. It was not until the year 1900 
 
 1 Walter, "Genetics," p. 164. 
 
138 THE BREEDING OF ANIMALS 
 
 that three great investigators, De Vries in Holland, Von 
 Tschermak in Austria, and Correns in Germany, simul- 
 taneously discovered the published results of Mendel and 
 recognized their great fundamental importance. 
 
 131. The experiments of Mendel. — Mendel selected 
 for his experiments the common garden pea. It is not 
 certain that he fully recognized the wisdom of making 
 such selections as were finally made for his work, but at 
 any rate he selected two varieties of peas differing in a 
 simple character but each firmly fixed in the parent 
 variety. The peas were also self-fertilizing, and accidental 
 mixture by cross fertilization was thus avoided. The 
 characters selected by Mendel were " purple or white 
 flowers," " yellow or green cotyledons," and " round or 
 wrinkled seeds." He found that all of these characters 
 were firmly fixed and bred true. These varieties were 
 crossed and the progeny were bred pure for many suc- 
 ceeding generations. 
 
 He decided upon the simple character of color and 
 selected a green seeded and yellow seeded variety. Recip- 
 rocal crosses were made, and from each cross the result- 
 ing peas were all yellow. Because the yellow color in 
 the cross appeared in every case, he called it the dominant 
 character; and the green color which did not appear in 
 the first generation was called a recessive character. 
 
 All the yellow seeds of the first generation resulting 
 from the original cross were planted. In the second 
 generation Mendel discovered that both green and yellow 
 seeds appeared. In calculating the relative proportion 
 of the two colors, he found that about one-fourth of the 
 seeds were green and the remaining three-fourths yellow. 
 The green seeds and yellow seeds were planted separately 
 and it was found that the green seeds produced only 
 
HEREDITY 139 
 
 green seeds. They were planted for several generations 
 and always came true, showing no yellow character. 
 When the yellow seeds were planted, however, Mendel 
 found that a certain proportion of the yellow seeds had 
 both green and yellow offspring and a certain proportion 
 had only yellow offspring. The latter remained fixed 
 and true in character when bred for several generations. 
 The results of these investigations carried through 
 many generations indicated that there was a certain 
 mathematical ratio traceable in the offspring resulting 
 from the crossing of these two distinct varieties of peas. 
 In these results Mendel found that in the first genera- 
 tion the dominant character (yellow seed) appeared to 
 the exclusion of the green color. In the second genera- 
 tion he found that 25 per cent of the offspring were green 
 and 75 per cent apparently yellow. If the green peas 
 were planted, they produced only green peas, but when 
 the yellow peas were planted, they produced 25 per cent 
 pure yellow, 50 per cent mixed or hybrid (yellow and 
 green), and 25 per cent pure green. The pure yellows 
 and pure greens continued to breed true, but the 50 per 
 cent '' hybrid " peas continued to split up in each genera- 
 tion in the proportions of 25 per cent pure green, 25 per 
 cent pure yellow, and 50 per cent hybrid. 
 
 132. The law of dominance. — From these results 
 Mendel formulated the law of dominance, which is that 
 when two contrasting characters are bred together the 
 offspring in the first (Fi) generation will all exhibit the 
 dominant character. 
 
 133. The law of segregation. — When the individuals 
 comprising the first generation are interbred, the resulting 
 offspring (F2 generation) will possess the characters in 
 the proportion of three of the dominant character to one 
 
140 
 
 THE BREEDING OF ANIMALS 
 
 of the recessive. The recessive character is pure and will 
 breed true. The individuals possessing the dominant 
 character will be made up of one-third pure dominants 
 and two-thirds hybrid dominants in which the recessive 
 
 Dornimnt 
 
 Recessive 
 
 Y(yeJIoW) 
 
 dc green) 
 
 Y(Q.) ihyhrjd yeJhwy 
 
 (pureyeJlow)Yy ^VtGj QG Cjoure ^een) 
 
 ix icm GG 
 
 I)^) 2g[ 
 
 Fig. 16. 
 
 Diagram illustrating mendelian inheritance of yellow and 
 green characters in the garden pea. 
 
 character will reappear in the next generation. This may 
 be more clearly shown in the preceding diagram (Fig. 16). 
 Mendel's hypothesis affirms that when animals or 
 plants of contrasted characters are bred together, these 
 characters do not blend in the germ-cells of the offspring. 
 
HEREDITY 141 
 
 Fifty per cent of the germ-cells will contain the dominant 
 character and fifty per cent the recessive character. This 
 is true of both male and female germ-cells. 
 
 134. Unit characters. — Mendel's theory presupposes 
 the existence of unit characters, so-called because they 
 are transmitted as independent units. There exist in 
 every organic being a very large number of unit char- 
 acters, and these may be determined by experimental 
 breeding. Up to the present time a relatively small 
 number of unit characters have been definitely differ- 
 entiated and described, but our knowledge in this direc- 
 tion is being rapidly extended. 
 
 135. Gametic purity. — In one stage of maturation 
 of the male and female germ-cells, the nucleus of each 
 contains but half the normal number of chromosomes 
 characteristic of the species. This is the final stage in 
 the maturation process before fertilization takes place. 
 The germ-cells in this stage are called gametes. The 
 fertilized egg-cell which results from the union of a ma- 
 ture sperm and egg-cell (gametes) is called a zygote 
 (fertilized egg-cell). The zygote, therefore, contains the 
 normal number of chromosomes characteristic of the 
 species, one-half derived from the Qgg and one-half from 
 the sperm-cell. Gametic purity is a term used to desig- 
 nate the discontinuous nature of unit characters. The 
 gamete in Mendel's pea contains the factor necessary for 
 the production of yellow seeds, or it does not.^ 
 
 The terms homozygous and heterozygous were pro- 
 posed by Bateson to designate the fundamental consti- 
 tution of the germ-cells in respect to inherited characters. 
 " An individual is said to be homozygous for a given 
 
 1 Darbishire, ** Breeding and the Mendelian Discovery," 
 p. 217. 
 
142 THE BREEDING OF ANIMALS 
 
 character when it has been formed by two gametes each 
 bearing the character, and all the gametes of a homozygote 
 bear the character in respect of which it is homozygous. 
 When, however, the zygote is formed by two gametes of 
 which one bears the given character while the other does 
 not, it is said to be heterozygous for the character in 
 question, and only half the gametes produced by such a 
 heterozygote bear the character. An individual may be 
 homozygous for one or more characters, and at the same 
 time may be heterozygous for others." ^ 
 
 The conception of " gametic purity " as originally 
 stated requires some modification. It is no longer held 
 that characters are transmitted as units, but rather the 
 factors which combine to form characters. The factors 
 are so far purely imaginary. 
 
 When mendelism was first seriously considered, there 
 was no doubt among its most enthusiastic exponents 
 that the characters existed in a pure unmixed state in 
 the gamete.^ 
 
 136. Application of Mendel's law. — Can the practical 
 breeder apply the principles of heredity embodied in 
 Mendel's law to the improvement of the domestic ani- 
 mals ? The domestic animals are valued by man because 
 of certain desirable characteristics which they possess. 
 These characteristics are clearly recognized by the breeder. 
 The meat animal is produced because it is endowed with 
 certain qualities which give it a special value either to 
 the consumer or the producer. The dairy cow is highly 
 prized because she has the ability of producing large 
 quantities of milk, cream or cheese. The horse is the 
 burden-bearer. Its value depends on the amount 
 
 iPunnett, "Mendelism," 1913, p. 28. 
 
 ^See Castle, " General Heredity," vol. V, No. 3, p. 93. 
 
HEREDITY 143 
 
 of energy it can develop either in tractive power for pull- 
 ing heavy loads or in the form of speed or graceful action 
 for the pleasure of the owner. Other animals are main- 
 tained in a state of domestication for other values of 
 various kinds which contribute to the food, clothing or 
 pleasure of man. In a sense the producer of live-stock 
 may be compared to a manufacturer who employs capital, 
 labor, raw^ materials and efficient machines for the pro- 
 duction of more desirable and concentrated products. 
 In this comparison the raw materials are the grain, hay 
 and grass ; and the efficient machine is the animal. The 
 farmer's success and the interests of the consumer as 
 well are greatly dependent upon the efficiency of this 
 animal machine. Can Mendel's law be utilized in the 
 efforts of the breeder to increase the efficiency of animals ? 
 If so, what does the breeder need to know in order to 
 utilize the law of Mendel in further enhancing the value 
 of the prevailing types of domestic animals ? 
 
 137. The complexity of animal characters. — It must 
 be recognized in the beginning that the qualities which 
 are commonly mentioned by the breeder as highly desir- 
 able are generally the result of a combination of many 
 characters. These combinations do not behave as simple 
 unit characters. One of the first steps in the application 
 of Mendel's hypothesis to practical breeding must be to 
 analyze the valuable qualities of animals and determine 
 as far as possible the unit characters. It is probably 
 true that some combinations will behave in transmission 
 in the same manner as simple unit characters. But if 
 there are complex characters which behave in this manner 
 they must be determined by careful investigation. When 
 the qualities of an animal have been differentiated and 
 their behavior in transmission determined, then the prac- 
 
144 THE BREEDING OF ANIMALS 
 
 tical breeder may base his breeding methods upon the 
 principles of segregation and dominance which are founda- 
 tion stones in the theory of mendehan inheritance. 
 • It will also be important to remember that to utilize 
 the mendelian principle in the breeding of animals, the 
 breeder must be dealing with contrasting characters. 
 In the larger number of cases, the useful qualities of the 
 highly improved animals of the farm are but modifica- 
 tions of characters which were already present in the 
 wild forms. The function of milk secretion is common 
 to all mammals. The domestic cow is valuable because 
 this function has, through selection and skillful mating, 
 been gradually improved. The quality of giving a small 
 quantity of milk found in the wild cow, and the quality 
 of giving a large quantity of milk as present in the highly 
 improved dairy cow, are not contrasting characters. 
 The one is but a modification of the other and is probably 
 the result of accumulated fluctuating variations which 
 have been preserved by methodical selection. It will be 
 interesting to note here some characters among animals 
 which have already been found to conform to Mendel's 
 law. 
 
 138. The inheritance of polled and horned character 
 in cattle. — Examples of Mendel's law are much more 
 frequent among plants than animals. The complicated 
 nature of animal characteristics has made it difficult to 
 trace the workings of Mendel's law so far as it is related 
 to many animal characters. It is also more difficult 
 to find contrasting characters. An exception to the 
 above must be noted in the case of the horned and polled 
 characters in cattle. Whenever a pure polled animal 
 is mated with a pure horned animal, the offspring in the 
 first generation are all polled. If the first generation 
 
HEREDITY 
 
 145 
 
 offspring are interbred, the polled and horned characters 
 separate in the second generation in the proportion of 
 25 per cent pure polled, 50 per cent hybrid polled, and 
 25 per cent pure horned. The pure polled individuals, 
 
 Po//e</ 
 
 Homed 
 
 PiHY 
 
 PP' z W PP' 
 
 PP zPlH) HH 
 
 PP PP PP zP(H) 
 
 1- Polled Ny6r,d 
 
 2- Pure Polled 
 
 3- Pure Homed 
 
 Fig. 17. — Diagram illustrating mendelian inheritance as exhibited 
 in the transmission of polled and horned characters in domestic cattle. 
 
 if bred to others of their own kind, produce only pure 
 polled offspring. If the pure horned offspring likewise 
 are mated with pure horned individuals, their offspring 
 produce pure horned offspring. If the 50 per cent hybrid 
 polled individuals are bred to other hybrid animals, the 
 
146 THE BREEDING OF ANIMALS 
 
 result is the same as in the second generation. The off- 
 spring will be 25 per cent pure polled, 25 per cent pure 
 horned, and 50 per cent hybrid polled. (See Fig. 17.) 
 
 This principle has been repeatedly used in the produc- 
 tion of polled breeds of cattle. The only practical diffi- 
 culty is encountered in determining which of the second 
 generation are pure polled and which are hybrid polled. 
 This difficulty can be overcome only by repeated matings 
 and by observation of the offspring. 
 
 139. Theory of pure lines. — The practical breeder 
 of animals has depended almost entirely upon methodical 
 selection for the improvement of domestic animals. It 
 was Darwin's opinion that the improvement accom- 
 plished in the desirable qualities of animals and plants 
 was due to the persistent selection of desirable continuous 
 variations. In bringing about improvement, therefore, 
 the breeder only required keen powers of observation 
 to detect any variations in a standard sort which were 
 better than the qualities of the ancestors. By selecting 
 these varieties and continuing this process for many gen- 
 erations, highly improved sorts were ultimately developed 
 which came true when bred together. 
 
 In the practical application of this theory, it has been 
 frequently discovered that the limits of improvement 
 through selection were quickly reached. Apparently 
 the degree of improvement could not be carried beyond 
 a certain definite point. In a more careful analysis of 
 the fundamental basis of improvement by selection, 
 Johanssen ^ has demonstrated that very many of the 
 domestic plants are not possessed of single characters 
 only, but are a mixture. The selection exercised* by 
 man in such cases is essentially a process of selecting out 
 
 1 Johanssen, 1909, "Elemente der exakten Erblichkeitslehre." 
 
HEREDITY 147 
 
 the most desirable strain and gradually eliminating the 
 less desirable. This is the pure line theory and is now 
 generally accepted as applying to many cases of improve- 
 ment, especially among plants. 
 
 An acceptance of this theory recognizes the fact that 
 no amount of selection can improve a pure line after it 
 has been separated by continuous selection. 
 
 An hypothetical example of pure line selection among 
 animals might be imagined in the case of the wool of sheep. 
 The wool produced under a given set of environmental 
 conditions in a flock of sheep might vary from eight to 
 twelve pounds. In the germ-cells of a given individual, 
 we may assume that determiners are present for the pro- 
 duction of eight, ten and twelve pounds. In breeding, 
 these varying tendencies may be separated. It is con- 
 ceivable that some of the offspring may have inherited 
 the tendency to produce twelve pounds of wool, while 
 others may have inherited the tendency to produce eight 
 pounds. Through many generations of intelligent selec- 
 tion, the flock-master may bring about a more or less 
 complete separation of the tendency to produce twelve 
 pounds of wool and may thus increase the average pro- 
 duction of wool from his flock. The application of this 
 theory to animal-breeding is more difficult than to self- 
 fertilizing plants, but the difficulties are partially removed 
 by close interbreeding. 
 
 140. Hallett's wheat-breeding. — The pure line method 
 of breeding probably explains Hallett's unusual success 
 in the improvement of wheat in Great Britain. However, 
 it must be said that Hallett believed that improvement 
 within a pure line of selection was possible. Hallett's 
 method may be best described by using his own words : 
 
 " A grain produces a ^ stool ' consisting of many ears. 
 
148 THE BREEDING OF ANIMALS 
 
 I plant the grains from these ears in such a manner that 
 each ear occupies a row by itself. ... At harvest, 
 after the most careful study and comparison of the stools 
 from all these grains, I select the finest one, which I 
 accept as proof that its parent grain was the best of all, 
 under the peculiar circumstances of that season. This 
 process is repeated annually, starting each year with 
 the proved best grain, although the verification of this 
 superiority is not obtained until the following harvest. 
 
 " During these investigations no single circumstance 
 has struck me as more forcibly illustrating the necessity 
 of repeated selection than the fact, that of the grains in 
 the same ear one is found greatly to excel the others in 
 vital power." ^ 
 
 Hallett's experience has demonstrated, first, that 
 great improvement may be secured by this method of 
 selection. Second, he advocated the " ear to row " 
 method. Third, it is probable that the results may be 
 satisfactorily explained by Johanssen's pure line theory. 
 
 141. The presence and absence hypothesis. — In 
 Mendel's conception of the theory of dominant and reces- 
 sive characters, there existed a definite determiner for 
 both the dominant and recessive characters. Each char- 
 acter appeared in the gametes in a definite form. Later 
 investigations have pointed to the fact that the dominant 
 character may be due to the presence of a specific deter- 
 miner, while the recessive character may be due to its 
 absence. This conception of the behavior of the mende- 
 lian pair of characters is quite different from MendeFs 
 explanation. 
 
 The presence and absence theory has contributed 
 materially to the science of genetics. This hypothesis 
 
 ^ Journal of the Royal Agricultural Society, vol. 22, p. 371. 
 
HEREDITY 149 
 
 has made it possible to harmonize many of the observed 
 phenomena with the mendeUan principle. It has also 
 directed the attention of investigators to the fundamental 
 nature of the characters themselves. Great progress 
 will undoubtedly be made in the future in the direction 
 of a more thorough study and consequently better under- 
 standing of the real nature of the characters of both plants 
 and animals. 
 
 In the investigations on the eye color of man, it has 
 been found that the dominant character is due to a brown 
 pigment, while the recessive character is the result of the 
 absence of this pigment. Darbishire ^ has clearly indi- 
 cated the application of this theory in the case of the 
 round pea and the wrinkled pea. The quality of round- 
 ness or wrinkledness as found in the garden pea is due 
 to a difference in the amount of starch in the pea. In 
 the case of the wrinkled pea, all of the sugar content is 
 converted into starch. In the round pea a much more 
 complete transfer of sugar to starch is accomplished. 
 The inference is that in the round pea there is present 
 something in the germ-cell that so affects the physiological 
 processes in the cell that the sugar is more or less com- 
 pletely turned to starch. The something which deter- 
 mines this change of sugar to starch in the round pea is 
 absent from the germ-cell in the wrinkled pea. There- 
 fore, we have two varieties of pea that are clearly different. 
 When the wrinkled pea and the round pea are crossed, 
 they behave in accordance with the mendelian law. It 
 is not necessary in this case to assume that the determiner 
 which ultimately results in a round pea is entirely absent 
 in the wrinkled pea, but it seems to be entirely correct 
 
 1 Darbishire, "Breeding and the Mendelian Discovery," p. 
 127. 
 
150 THE BREEDING OF ANIMALS 
 
 to assume that there exists an insufficient quantity of 
 this substance and hence an incomplete transposition of 
 sugar to starch in the wrinkled pea. 
 
 It is not at present possible to apply the presence and 
 absence hypothesis to all cases of apparent mendelian 
 inheritance. That it applies to a very large number of 
 characters is obvious, but as pointed out by Darbishire 
 there are many cases which cannot at the present time 
 be explained on this theory, and in fact will be obstacles 
 in the way of its general application. Some characters 
 seem to be dominant in one class of plants or animals 
 and recessive in another. The polled character in cattle 
 is unquestionably dominant, while the possession of horns 
 is a recessive. In the case of sheep the reverse seems to 
 be true. The white color of pigs is dominant to black, 
 but the black color of sheep is dominant to white.^ 
 
 142. The theory of mutations. — It is clear that all 
 improvements in the domestic animals must come through 
 variation. If the offspring was always an exact repro- 
 duction of the parent, improvement would be impossible. 
 But how have the improved qualities now possessed by 
 our domestic animals come about? Have these qualities 
 come through a gradual and continuous .series of changes, 
 each better than the last, or have they come through 
 sudden and radical variations ? A study of the ancestral 
 history of both plants and animals gives clear evidence 
 that new types have originated by both kinds of variation. 
 
 143. Two important classes of variation. — Darwin 
 recognized these two distinct types of variation, but 
 believed that the most important changes in organic 
 beings were due to small but gradual and continuous 
 variations in a given direction. In his earlier writings 
 
 1 Punnett, "Mendelism," p. 29. 
 
 i 
 
HEREDITY 151 
 
 Darwin emphasized the great importance of continuous 
 or fluctuating variations. He says, '' It may be doubted 
 whether sudden and considerable deviations of structure 
 such as we occasionally see in our domestic productions, 
 more especially with plants, are ever permanently prop- 
 agated in a state of nature. Almost every part of every 
 organic being is so beautifully related to its complex 
 conditions of life that it seems as improbable that any 
 part should have been suddenly produced perfect, as 
 that a complex machine should have been invented by 
 man in a perfect state." 
 
 Sudden variations were called by Darwin discontinuous. 
 Variations frequently occur which vary widely from 
 the parent form. Examples of this kind of variation 
 are common in both plants and animals. The normal 
 fruit of a peach tree is a typical peach having a rough 
 skin and a flavor and color peculiar to the peach. 
 Branches of peach trees, however, sometimes produce a 
 fruit known as a nectarine. This is smooth, smaller 
 than the peach, and possessed of a color, flavor and physical 
 consistence markedly different from the normal fruit of 
 the peach. 
 
 Among animals mutations frequently occur. Varia- 
 tions in the number of digits have been recorded by a 
 large number of investigators. Huxley describes the 
 case of a man born with six fingers on each hand and six 
 toes on each foot. Four children were born to this man. 
 The first, a male child, was born with six fingers on each 
 hand and six toes on each foot. The second child, a 
 boy, had five fingers and five toes, but one toe was de- 
 formed. The third child, also a boy, had five perfect 
 fingers and toes, but the fourth child, a girl, although 
 having the normal number of digits, had deformed thumbs. 
 
152 THE BREEDING OF ANIMALS 
 
 The mutation appearing in the father was not only a 
 radical variation, but there existed a strong tendency to 
 transmit the abnormality. The strength with which 
 mutations are transmitted is still further indicated by 
 the later history of the sons and daughters of the father. 
 " Salvator had four children — they were two boys, a 
 girl, and another boy — the first two boys and the girl 
 were six-fingered and six-toed like their grandfather; 
 the fourth boy had only five fingers and toes. 
 
 " George had only four children ; there were two girls 
 with six fingers and six toes ; there was one girl with six 
 fingers and five toes on the right side, and five fingers -and 
 five toes on the left side, so that she was half-and-half. 
 The third, Andre, you will . recollect, was perfectly well 
 formed, and he had many children whose hands and feet 
 were all regularly developed. 
 
 " Marie, the last, who of course married a man who 
 had only five fingers, had four children : the first, a boy, 
 was born with six toes, but the other three were normal." ^ 
 
 Some marked variations among the domestic animals 
 which have been recorded from time to time and which 
 are probably true mutations may be mentioned. The 
 normal foot of domestic swine is cleft, but solid-hoofed 
 hogs are common, and this mutation is strongly trans- 
 mitted. The breed of swine known as " mule-footed 
 hogs " is an example. Horned sheep normally possess- 
 ing two horns are sometimes born with four horns. The 
 offspring of horned cattle are sometimes born without 
 horns, and this variation is strongly transmitted. 
 
 To Hugo De Vries of Amsterdam we owe our present 
 definite notions regarding the theory of mutations. While 
 such variations were recognized by Darwin and other 
 
 1 Huxley, quoted in Miles' "Stock Breeding," p. 79. 
 
HEREDITY 153 
 
 investigators, it remained for De Vries to demonstrate 
 by scientific investigation the important role played by 
 mutations in the evolution of plants and animals. This 
 theory undertakes to explain the origin of species by sud- 
 den marked variations rather than by continuous or 
 fluctuating variations. De Vries* experiments were suc- 
 cessful not only in demonstrating clearly the remarkable 
 tendency of certain species to vary abruptly, but of even 
 more significance was his demonstration of the fact that 
 such variations were as surely transmitted as were the 
 regular or normal characters of the species. 
 
 It is true, mutations must not be confounded with 
 the appearance of freaks or monstrosities among plants 
 and animals. Often through arrested development or 
 accidental injury during the embryonic existence of ani- 
 mals, certain characteristics may become so modified 
 that they appear in the form of new characters. Such 
 freaks are not transmitted and are not therefore muta- 
 tions. The term mutations is used only to designate 
 those variations which are heritable. 
 
 144. Kinds of mutations. — Mutations may be addi- 
 tions or improvements to the life of organic beings, or 
 they may result in diminishing the ability of an animal 
 or plant to live and thrive in an ordinary environment. 
 De Vries has therefore suggested a classification of muta- 
 tions as progressive, regressive and degressive. 
 
 Progressive mutations are those which have contrib- 
 uted something entirely new. It is in reality an addi- 
 tional character. Attention has already been called 
 to cases of variation in which the offspring is provided 
 with extra fingers or toes. An example of this form of 
 mutation is described by Alexander Graham Bell in the 
 ease of multi-nippled sheep. 
 
154 THE BREEDING OF ANIMALS 
 
 In regressive mutations the animal actually loses 
 some hereditary character that it has formerly possessed. 
 An animal may be born with less than the normal number 
 of digits, and this may be transmitted to offspring. The 
 so-called tailless breed of cats is probably descended 
 from an individual born without a tail. A polled animal, 
 the offspring of horned parents, would also be an example 
 of regressive mutation. 
 
 The term degressive has been applied to such varia- 
 tions as have existed in the previous ancestral history of 
 the animal or plant. When such variations reappear 
 after many generations, they are known as degressive 
 mutations. 
 
 145. Importance of the mutation theory. — The im- 
 portance of the mutation theory to the animal-breeder 
 lies in the fact that many of the most important and useful 
 qualities present in the domestic animals have probably 
 arisen through sudden variations or mutations. Such 
 mutations are likely to occur at any time. It is indeed 
 probable that such mutations do occur frequently. The 
 intelligent breeder who understands the laws of evolution 
 will clearly recognize the importance of such mutations. 
 The fact that they are certainly transmitted by heredity 
 has given to the breeder a most important method in 
 the permanent improvement of the domestic animals. 
 It is, of course, quite as true that mutations may be 
 degressive and thus actually be of less value than the par- 
 ent forms. Certain breeds are probably more variable 
 than others, and this fact may be both an advantage and 
 a disadvantage. It is a desirable condition in that mu- 
 tations may occur and some of these may be improve- 
 ments over the parent species. Such a tendency to vary 
 may be a disadvantage in that the variations may some- 
 
HEREDITY 155 
 
 times be in the direction of less valuable characters. 
 Eventually no breed of animals can be most useful until 
 the desirable characters are firmly fixed and reasonably 
 certain to be transmitted by inheritance. 
 
 146. Mono-hybrids and di-hybrids. — In all of the 
 examples so far used to illustrate the principles of segrega- 
 tion and dominance as developed by Mendel, only such 
 simple unit characters have been employed as indicate 
 clearly the law of Mendel. Such simple contrasting 
 characters are known as mono-hybrid. It is easy to 
 demonstrate the mendelian hypothesis in the case of 
 mono-hybrids. 
 
 But among domestic animals the qualities which have 
 made organic beings useful to man are in most part a 
 combination of two or more unit characters. In such 
 cases it is far more difficult to use the mendelian formula. 
 Mendel himself determined the probable application of 
 the principle to cases where two different unit characters 
 were present. He crossed the wrinkled green peas with 
 smooth yellow peas. Manifestly, the number of com- 
 binations of characters was greater than when mono- 
 hybrids were examined. The proportion of 3 plus 1 is 
 the universal result in the Fi generation where single unit 
 characters are involved. Mendel found in the case of 
 combinations of two unit characters that the mathemat- 
 ical statement (3 plus 1)^ (16) represented the true 
 result. There would appear sixteen possible zygotes as 
 a result of crossing individuals containing two unit 
 characters in each of the parents. In the offspring result- 
 ing from such crosses the characters would be combined 
 in such a manner as to produce sixteen kinds of indi- 
 viduals. 
 
 It is apparent that if the number of combinations of 
 
156 THE BREEDING OF ANIMALS 
 
 unit characters increases, the number of possible different 
 individuals produced by crossing similarly increases. 
 In the case of tri-hybrids in which three characters com- 
 bine, the number of different individuals or zygotes pro- 
 duced would be represented by (3 plus 1)^. For the 
 purposes of the practical breeder, therefore, little progress 
 is possible except in cases where one or two characters 
 only are involved. In those cases in which the characters 
 involved are made of a combination of many units it is 
 first necessary that the important unit characters be 
 separated by long-continued breeding; in other words, 
 until it becomes homozygous. By such methods, it is 
 possible to obtain recombinations, and from the point 
 of view of the practical breeder, entirely new characters. 
 The mendelian principle may, therefore, in this way be- 
 come a powerful instrument in the future improvement of 
 domestic plants and animals. 
 
CHAPTER VIII 
 INHERITANCE OF ACQUIRED CHARACTERS 
 
 The normal characteristics of all organic beings may 
 be greatly modified by external conditions acting con- 
 tinuously upon the organism for a longer or shorter 
 period of time. Such modifications may be of so marked 
 a character as to cause an apparent departure from the 
 average or normal characteristics of the race. Through 
 accident, disease or by design, the animal or plant may 
 become permanently mutilated. The modifications which 
 result from the causes mentioned may make the domestic 
 animal or plant more useful to man than the normal 
 organism ; the changes may in fact be real improvements, 
 and as such it would be very desirable to perpetuate 
 them by heredity. Thus the breeder of domestic ani- 
 mals, having accurately observed the general fact of 
 inheritance of the normal characters, has reasoned that 
 such remarkable changes as those often resulting from 
 use or disuse, favorable environment or mutilations must 
 be transmitted with equal force. 
 
 147. Belief in transmission of acquired characters. — 
 The literature of the ancients indicates that the philos- 
 ophers of that period believed in the inheritance of 
 acquired characters. Aristotle mentions the transmission 
 of the exact shape of a cautery mark. At a much later 
 period Lamarck elaborated his theory of variation and 
 selection which took for granted that all modifications 
 
 157 
 
158 THE BREEDING OF ANIMALS 
 
 resulting from use and disuse and the effects of environ- 
 ment were transmitted by heredity.^ 
 
 Among those who have failed to find satisfactory 
 evidence of the inheritance of modifications must be 
 mentioned Kant, Blumenbach, and later Galton, Weis- 
 mann, Ray Lankester and practically all the leading 
 biologists of modern times. 
 
 148. Practical breeders believe in transmission of 
 acquired characters. — There is a widespread belief 
 among the breeders of domestic animals that acquired 
 characters are inherited. To the practical breeder of 
 dogs who has observed the sensitive reaction of the fox 
 hound to the scent of the fox, or the alertness of the setter 
 or pointer in the presence of a fresh bird track, it is diffi- 
 cult to find a satisfactory explanation for existing facts 
 without assuming that the results of the training of a 
 dog to some extent must be transmitted. Extreme speed 
 in running and trotting horses is the result of training 
 and exercise. The offspring of parents who have acquired 
 extreme speed through training and exercise are more apt 
 to possess the ability to acquire similar extreme speed 
 than the offspring of parents who have not been trained. 
 The practical breeder concludes, therefore, that the ac- 
 quired speed must be transmitted. 
 
 There are many breeders of beef cattle who firmly 
 believe that by maintaining the breeding animals in high 
 condition, the calves will have a more pronounced devel- 
 opment of those characters which are recognized as 
 belonging to the beef type than will the calves of parents 
 which are maintained on a low plane of nutrition. 
 
 The breeder is an accurate observer, and there can be 
 no question that his facts are generally correct in this 
 
 1 Thomson, "Heredity," p. 170. 
 
INHERITANCE OF ACQUIRED CHARACTERS 159 
 
 instance as in many others. But the biologist could 
 easily explain the facts cited upon wholly different grounds. 
 The fact that the trotting horse parents could be developed 
 to high speed indicated clearly that they had inherited a 
 capacity for such development. The offspring inherited 
 the same capacity and under the same favorable condi- 
 tions would develop the same speed. The breeder of 
 beef cattle is in general correct in his practice when he 
 maintains his breeding animals on a high plane of nutri- 
 tion, not because such treatment in any way influences 
 the fundamental constitution of the germ-plasm, but 
 because this is a satisfactory method of determining which 
 breeding animals possess the fattening tendency. Those 
 parents that show the capacity for rapid and economical 
 fattening are preserved and the unthrifty are eliminated 
 from the breeding herd. The high plane of feeding is a 
 method of selection. 
 
 149. Nature and nurture. — The nature of an animal 
 is determined by heredity. What an animal may become 
 is limited by its inheritance. What an animal actually 
 becomes is often largely determined by the use made of 
 its inheritance. The individual may inherit great possi- 
 bilities, but these may never be realized because unde- 
 veloped. The characteristics of an individual, then, are 
 the result of both nature (heredity) and nurture (develop- 
 ment). 
 
 The tremendous importance of nurture to the indi- 
 vidual is demonstrated by numerous examples. The 
 untrained trotting horse may have inherited the same 
 possibilities for development as his stable mate, but 
 because of superior opportunity through skillful training 
 the latter makes a new trotting record while the former 
 achieves nothing. 
 
160 THE BREEDING OF ANIMALS 
 
 The most notable examples of acquired development 
 are to be found in the human family. Through the life- 
 time of a man the mental and physical qualities may be 
 greatly modified. An individual may acquire great 
 mental power. Such acquirement may have been 
 achieved under very great difficulties. The particular 
 kind of mental efficiency represented by the develop- 
 ment of such an individual may be an exceedingly desir- 
 able characteristic of the greatest value to the human 
 race. Its transmission by heredity would be desirable 
 for the good of the race. Can such acquired characters 
 or habits be transmitted? The answer to this question 
 is important to the development of the human race. It 
 is likewise of the greatest economic importance to the 
 breeder of domestic animals. In the domestic animals 
 the highly artificial characters possessed by the improved 
 forms of cattle, horses, sheep and swine are very largely 
 due to the development or good handling to which these 
 animals have been subjected. If the results of the 
 high degree of development of one generation are to 
 fundamentally influence the characters of the next, then 
 a new significance will be given to the effects of environ- 
 ment. 
 
 150. What are acquired characters ? — The use of 
 the term acquired characters to indicate entirely different 
 facts has given rise to some confusion in the consideration 
 of this subject. In one sense no character is ever trans- 
 mitted. Only the determiners which give direction to 
 the developing characters of the animal or plant are 
 actually inherited. The characters themselves develop 
 out of and are determined by the fundamental constit- 
 uents of the germ substance. Thus the appearance of 
 the secondary sexual characters of the male at puberty 
 
INHERITANCE OF ACQUIRED CHARACTERS 161 
 
 are not acquired characters in the biological sense. Ac- 
 quired characters are modifications of the somatic cells 
 which are induced by environment, use or disuse, acci- 
 dents or any other influences acting upon the body-cells 
 in such a way as to change their normal development. 
 According to Weismann, if the modifications are the result 
 of the presence of determiners in the germ-plasm, then 
 they are not properly designated as acquired characters. 
 
 151. Somatoplasm and germ-plasm. — From the view- 
 point of the biologist, all organic beings which reproduce 
 sexually are differentiated into two very clearly defined 
 groups of cells : the somatic group, which includes all 
 the cells concerned in the processes of nutrition, includ- 
 ing digestion, absorption and assimilation; the nerve 
 cells and all other cells involved in the physiological 
 activities of the organized being, except the reproductive 
 cells. 
 
 Distinct and apart from the soma- or body-cells are 
 the germ-cells, the function of which is to provide for 
 the reproduction of the species. Weismann was the 
 first to point out clearly the very sharp division between 
 the fundamental organization and function of these two 
 groups. The somatoplasm has its origin in the germ- 
 plasm, and the direction of its development is controlled 
 by the determiners in the germ-plasm, but the germ- 
 plasm is not influenced in any fundamental way by the 
 somatoplasm. The soma is to be regarded in the nature 
 of a habitat for the successful activities of the germ-cells. 
 In a sense, the somatoplasm has no more influence upon 
 the developing germ-cells harbored within the soma than 
 does the soil upon the trees which may develop from 
 the seeds planted on its surface. 
 
 The germ-plasm is continuous. It is a part of the 
 
 M 
 
162 THE BREEDING OF ANIMALS 
 
 germ-plasm of the preceding generation. If this dis- 
 tinction and differentiation is kept clearly in mind, it 
 will help materially in the discussion of the inheritance 
 of acquired characters. If we accept Weismann's def- 
 inition of acquired characters, that they are somatic 
 modifications which do not have their origin in the germ- 
 plasm, we have to discuss only such somatic modifications 
 as may be acquired by the animal during its lifetime. 
 
 152. Examples of acquired characters. — Among the 
 common causes of the changes in the soma must be 
 grouped environment, including food and climate; use 
 and disuse of parts ; disease and accidents. Each of 
 these acting separately or all of them acting together may 
 cause profound changes in the external form and develop- 
 ment of plants and animals. 
 
 153. Food supply. — Perhaps no other single environ- 
 mental influence is responsible for such profound changes 
 in the external form of plants and animals as the food 
 supply. The Kerry cattle of Ireland are a diminutive 
 race of cattle which have been long subjected to condi- 
 tions of scant supply of innutritions food. Their size 
 and hardy character must be regarded as a more or less 
 successful adaptation to their environment. When young 
 calves of the Kerry breed are surrounded with conditions 
 in which they are supplied with a generous and nutri- 
 tious food, they increase in size and come to maturity 
 at an earlier age.^ 
 
 The Shetland pony in the barren islands of Shetland, 
 gathering a scant subsistence from the inferior grasses 
 and forage plants, develops into one of the most diminu- 
 tive races of horses known to man. The same race of 
 horses transplanted to the fertile regions of Great Britain 
 
 1 Miles, "Principles of Stock Breeding," p. 100. 
 

 
 
 
 
 - "^JSLAlJv.^^^^BPMlft 
 
 4 
 
 j 
 
 ^ 
 
 1 
 
 
 
 
 1 
 
 ^^Uj^ %£ ':7l 
 
 ^ 
 
 
 
 
 1 
 
 rmk^. 
 
 
 
 IIJII^""", / 
 
 
 1 
 
 
 
 
 Iflpi^''^^^ 
 
 
 I 
 
 ^^^^^^^E- 
 
 
 
 Sp" 
 
 . '^^ 
 
 1 
 
 ". s.'^!^8 
 
 J^* ^ V 
 
 MM^^^' ^ 
 
 
 Plate VII. — Upper. Ration not restricted. Fed for rapid growth 
 and development from age 90 days. Age 716 days, weight 1401 pounds. 
 Lower. Ration greatly restricted. Age 777 days, weight 512 pounds, 
 height 121 cm. 
 
i 
 
Plate VIII. — Upper. Ration not restricted. Fed for rapid growth 
 and development from age 90 days. Age 336 days, weight 875 pounds. 
 Lower. Ration partially restricted. Fed for normal but moderate 
 growth and development. Age 780 days, weight 813 pounds, height 
 128 cm. Compare with Plate VII. 
 
INHERITANCE OF ACQUIRED CHARACTERS 163 
 
 or America increases in size as the result of a better food 
 supply. 
 
 Woltereck, by changing the food supply only, in hyalo- 
 daphnia, succeeded in changing the percentage of the 
 height of the head to that of the body from 40 to over 90. 
 
 The remarkable influence of the amount of food supplied 
 to an animal during its development in modifying the 
 somatic cells and changing the external form of animals, 
 is well illustrated by the unpublished results of an experi- 
 ment conducted at the Missouri Experiment Station.^ 
 In this investigation, the animals were maintained for 
 long periods upon different planes of nutrition. 
 
 For the purpose of this investigation the animals were 
 divided into three groups. Group one (see Plates VII, 
 VIII and IX) was supplied with a generous ration cal- 
 culated to furnish to the animal all the nutrients it 
 could utilize, and produce the maximum growth and 
 development, including the laying on of fat. The treat- 
 ment given to group one resulted not only in very 
 rapid growth and development, but as the excessive 
 feeding was long continued, the animals laid on unusual 
 and excessive amounts of fat. 
 
 The ration supplied to group two (see Plate VIII, 
 lower) was intended to provide such a quantity of food 
 as was sufficient to produce strong, healthy growth and 
 development, but insufficient for laying on any consider- 
 able amount of fat. This ration resulted in normal, 
 healthy growth, but the food supplied was constantly 
 below the desires and appetites of the animals. There 
 was no time during the experiment at which the animals 
 would not have consumed more food. 
 
 ^ Waters and Trowbridge, Unpublished Data from the Mis- 
 souri Experiment Station. 
 
164 THE BREEDING OF ANIMALS 
 
 Group three (Plate VII, lower) was limited markedly in 
 the amount of food which the animals were permitted to 
 consume. The scant ration given to group three did not 
 prevent the animals from growing, but it did prevent the 
 animals from making a normal growth, and prevented the 
 normal deposition of fat within the body tissues, which 
 seems to be a favorable factor, in inducing healthy growth 
 and development. 
 
 The illustrations represent typical animals in the three 
 groups. These illustrations give a general impression 
 of the changes in body form which are readily apparent 
 to the eye, resulting from the methods of treatment of 
 these various groups. 
 
 154. Influence of the amount of food on body weight. — 
 A record of the changes in the body weight of an animal 
 is not the most accurate measure of the influence of any 
 environmental factor, but it is sometimes very useful, 
 and often the best measure available. In this experi- 
 ment, animal 501, which was fed for forty-seven months 
 on a full ration, attained in that time a total weight of 
 1965 pounds. Animal 512, fed a medium ration for 
 forty-eight months, attained a weight during that period 
 of 1224 pounds. Animal 500, belonging to the low-fed 
 group, weighed, at the end of the forty-eight months' feed- 
 ing, 1042 pounds. The differences observed in these 
 animals must be due entirely to the differences in the 
 amount of food supplied, as they were subjected to iden- 
 tical conditions in all other respects. The experiment 
 would have been still more valuable if the animals in the 
 three groups had been fed on the different rations from 
 birth. As a matter of fact, the animals in all the groups 
 were generously fed during the first five months of their 
 lives. 
 
h:^-s^^^. 
 
 Plate IX. — Upper. Steer 527 weighing 200 pounds at age 120 
 days. Fed maximum ration for rapid growth and development from 
 age 90 days. Lower. Same, weighing 1453 pounds at age 27 months ; 
 rations not restricted. 
 
INHERITANCE OF ACQUIRED CHARACTERS 165 
 
 155. Food supply and body changes. — All the evi- 
 dence available points to the fact that the domestic ani- 
 mals have inherited not only a tendency to reach a cer- 
 tain size and form, but that they have inherited a strong 
 tendency to attain a given size at a certain age. Thus, 
 in these investigations at the Missouri Experiment 
 Station, there is evidence to show that the animal organ- 
 ism makes desperate efforts to grow, even when the food 
 supply is greatly limited. In one case a calf nine-and- 
 one-half months old was fed a limited ration which 
 resulted in a loss of weight amounting to 82 pounds in 
 six months. During the same period this animal in- 
 creased 8.1 per cent in height and 14.1 per cent in length 
 of head.^ 
 
 156. Influence of limited food supply from birth. — 
 The amount of food supplied to a growing animal in a 
 large measure determines not only its ultimate develop- 
 ment, but the rate at which the animals grow. In another 
 investigation at the Missouri Experiment Station,^ three 
 animals were fed a full ration, a medium ration and a 
 scant ration, respectively. Animal number 527 (Plate VII, 
 upper) given a full ration, increased in weight rapidly, and 
 at the end of 789 days weighed 1453 pounds. Animal 559 
 (Plate VIII, lower), given a medium ration intended to 
 produce a normal growth, but not a fattening ration, at 
 the end of 780 days weighed 813 pounds. Animal 551 
 (Plate VII, lower) , given a scant ration, weighed at 777 days 
 512 pounds. It is, of course, possible that in these experi- 
 ments the differences in body weight may be due to the 
 
 ^ Waters, Proceedings of the Society for the Promotion of Agri- 
 cultural Science, 1908. 
 
 2 Waters and P. F. Trowbridge, Unpublished Data of the 
 Missouri Experiment Station. 
 
166 THE BREEDING OF ANIMALS 
 
 amount of fat deposited in the tissues rather than to differ- 
 ences in the development of the skeleton and muscular tis- 
 sues. The very great differences in weight noted are of the 
 greatest significance if they represent differences in the 
 fundamental skeletal and muscular tissues of the body. 
 If they represent alone differences in the amount of fat, 
 they are not so significant. The height of each animal 
 as observed seems to indicate clearly that not only is 
 the amount of fat deposited in the tissues directly 
 determined by the amount of food available, but the 
 skeletal growth also is profoundly influenced by the food 
 supply. 
 
 There can be no question but that limiting the amount 
 of food supplied to young animals has a profound influ- 
 ence upon the rate of growth as well as its ultimate size. 
 This influence is to be found in smaller skeleton, probably 
 arrested development of the muscular tissues, and a much 
 smaller percentage of fat. 
 
 157. Telegony. — There was a time when eminent 
 biologists and practical breeders firmly believed that the 
 influence of the sire was not confined to his immediate 
 offspring but the mother herself was in some manner so 
 impressed with the characters of the sire that her subse- 
 quent progeny sired by entirely different males might 
 take on the characters of the former sire. " The act of 
 fecundation is not an act which is limited in its effect," 
 says Agassiz,^ " but that it is an act which affects the 
 whole system, the sexual system especially; and in the 
 sexual system the ovary to be impregnated hereafter 
 is so modified by the first act that later impregnations 
 do not efface that first impression." Darwin supported 
 his belief in telegony by citing many cases among plants 
 
 ^ Massachusetts State Board of Agriculture, 1863, p. 56. 
 
INHERITANCE OF ACQUIRED CHARACTERS 167 
 
 of '' direct action of the male element on the mother 
 form." He remarks further that " the male element 
 not only affects, in accordance with its proper function, 
 the germ, but the surrounding tissues of the mother 
 plant." 
 
 Spencer likewise admitted the probability of the pas- 
 sage of the germ-plasm from the growing embryo into the 
 maternal tissues and thus to the germ-cells. Weismann 
 held that if any such influence in reality existed, it could 
 be explained only on the theory that some of the sperm- 
 cells of the male penetrated to the undeveloped ova and 
 there accomplished a partial impregnation. Some prac- 
 tical breeders, of horses and dogs particularly, were so 
 thoroughly impressed with the possibility of such an 
 influence that they would not buy a highly bred animal 
 that had borne offspring to another breed, believing that 
 such a female could not be trusted to breed true. Some 
 farmers in the mule-breeding districts have reported 
 that horse foals from mares which had previously pro- 
 duced mules, sometimes possessed " mulish characters." 
 These characters which are commonly possessed by the 
 hybrid appearing thus in pure horse foals were supposed 
 to have come about through the influence of the jack on 
 the mother at some previous mating. 
 
 158. The Lord Morton mare. — One of the most 
 striking cases of supposed infection was reported to the 
 Royal Society ^ by Lord Morton in 1820. 
 
 The essential facts are discussed by Darwin.^ In the 
 year 1815 Lord Morton bred a seven-eighths Arabian 
 mare of chestnut color to a quagga. The resulting 
 
 ^ Philosophical Transactions, 1821, p. 21. 
 2 Darwin, "Animals and Plants under Domestication," 
 vol. I. 
 
168 THE BREEDING OF ANIMALS 
 
 offspring was a true hybrid having the same color 
 and in other characters resembhng the sire. Later in 
 1817, 1818 and 1821 the same mare was bred to a black 
 Arabian stallion and from each mating produced a healthy 
 foal which in every case was marked with stripes like 
 the quagga sire, and resembling the sire also in the char- 
 acter of the mane. Lord Morton, in describing the 
 particular resemblances of these foals, says : " Both in 
 their color and in the hair of their manes they have a 
 striking resemblance to the quagga. Their color is 
 very marked, more or less like the quagga in a darker 
 tint. Both are distinguished by the dark line along the 
 ridge of the back, the dark stripes across the forehead 
 and the dark bars across the back part of the legs." ^ 
 The existence of stripes or bars on young foals is not 
 uncommon, and their presence on the offspring of the 
 Lord Morton mare may be explained on other grounds 
 than the assumption that they were caused by the influ- 
 ence of a previous impregnation of the Arabian mare by 
 the quagga sire. 
 
 159. The Penycuik experiments. — The possibility of 
 tracing to some other source the real or fancied resem- 
 blances of the Arabian foals to the quagga sire of a pre- 
 vious mating, led Cossar Ewart to make a thorough inves- 
 tigation of the so-called infection theory. At Penycuik 
 in 1895 Ewart repeated as closely as possible the breed- 
 ing experiment of Lord Morton. In these experiments 
 thirteen mares of varied colors and breeds produced a 
 total of sixteen foals to a Burchell zebra. The same mares 
 later produced twenty-two foals by Arab, Thoroughbred 
 and Highland stallions. Ewart, in describing a typical 
 
 1 Ewart, Bureau of Animal Industry Report, 1910, U. S. 
 Dept. of Agr. 
 
INHERITANCE OF ACQUIRED CHARACTERS 169 
 
 result, says : ^ " The first hybrid was born August 12, 
 1896, the dam being Mulatto, a black Highland pony 
 lent by Lord Arthur Cecil." 
 
 " In 1897 Mulatto had a foal to Benazrek, a gray Arab 
 stallion. As this subsequent foal of Mulatto was indis- 
 tinctly striped, I was at first inclined to believe she had 
 been infected by her first sire, the zebra Matopo ; but 
 when more richly striped pure-bred foals were obtained 
 later by Benazrek out of Highland mares which had never 
 even seen a zebra, it became evident that Mulatto af- 
 forded no evidence in support of the infection doctrine. 
 
 " Lord Morton's quagga counted for so little in the 
 hybrid out of the chestnut Arab mare that its right to 
 be regarded as a hybrid has been questioned. Matopo, 
 however, proved so impressive that all his hybrid offspring 
 plainly indicated their descent from a richly striped 
 zebra. 
 
 " On the other hand, the subsequent foals (by Arab 
 and other stallions out of the mares which proved fertile 
 with Matopo) differed so profoundly from hybrids (even 
 when, as was sometimes the case, they had bars on the 
 legs and faint stripes across the withers) that they afforded 
 no evidence that the first male influences ' the progeny 
 subsequently borne by the mother to other males.' " 
 
 Baron de Parana in Brazil produced many zebra 
 hybrids also from a true Burchell zebra, later rearing pure 
 horse foals from mares that had previous zebra hybrids. 
 In no single case did the stripes which did sometimes 
 appear resemble closely the striping of the zebra. 
 
 A somewhat extended inquiry by Romanes in 1893 
 
 1 Ewart, "The Principles of Breeding and the Origin of Do- 
 mesticated Breeds of Animals," Report of the Bureau of 
 Animal Industry, U. S. Dept. of Agr., 1910. 
 
170 THE BREEDING OF ANIMALS 
 
 in British and American live-stock journals developed 
 the fact that telegony is not as generally believed among 
 breeders of the present day as has been generally reported. 
 Sir Everett Millais, as the result of over fifty experiments 
 with mammals and birds, found no conclusive evidence 
 of infection. 
 
 Evidences of telegony, if it exists at all, ought to be 
 easily collected in those regions where the production of 
 mules is common. Darwin says,^ '' It is worthy of note 
 that farmers in South Brazil (as I hear from Fritz Miiller) 
 and at the Cape of Good Hope (as I have heard from two 
 trustworthy correspondents) are convinced that mares 
 which have once borne mules when subsequently put to 
 horses are extremely liable to produce colts striped like 
 a mule." 
 
 These conclusions are not supported by Baron de 
 Parana,^ who reports, " I have many relatives and friends 
 who have large establishments for the rearing of mules 
 where they obtain 400 to 1000 mules in a year. In all 
 these establishments, after two or three crossings of the 
 mare and ass, the breeders cause the mare to be put to a 
 horse because they believe that unless the mares are 
 changed after producing three mules they become sterile. 
 In all these establishments a pure-bred foal has never 
 been produced resembling either an ass or a mule." 
 
 160. Telegony and mule hybrids. — In the horse- 
 breeding districts of Missouri, large numbers of mules 
 are produced annually. Many of the mares which have 
 produced one or more mules are later bred to stallions 
 and thus become the dams of horse foals. The jack 
 and the stallion differ so widely in many important 
 particulars that any marked tendency of horse foals to 
 
 1 Report of the Bureau of Animal Industry, 1910, p. 123. 
 

 
 
 
 
 ■HM|^^^BH 
 
 ^^^A 
 
 
 ^^t^^^^^e C^ rt^^BL.a^^H 
 
 ^^^^^^^^^^^^^KH 
 
 ^^^^^^Kli.^ 
 
 j|»C«^»? 
 
 
 ^^^^^^^^^^^^^^^^^Kml 
 
 D^^^^^^Htl^l 
 
 ^Hl^ ' 
 
 Hm j'^IH.'' gjl^^^l 
 
 I^^^^^^^^^^^H 
 
 ^j^^^^^l 
 
 ^Hk 
 
 KKm'^'Iiv'' ^^^^^^ 
 
 ^^^^^^^^^^^H^^H 
 
 I^^^H^^Hl 
 
 ^Ht 
 
 mt ^w ^r\ 
 
 ^H ^^^!^^^^^^^^», , • 
 
 ^HH 
 
 v 
 
 m -^^^ W 
 
 1 
 
 ^t^m 1 
 
 P^ii''' 
 
 Mjl^ ^^^^SEBWkk:^ --s^^ III^B 
 
 mO„ 
 
 ^H^E^^^^Ir 
 
 V^ nHL 
 
 
 "■m/-jf *' ''f\'^ *~ ' ''*'<^'? !^ 
 
 IIBJ 
 
 • -r* 
 
 
 <JIHiMHMn|HHHH 
 
 URk^ 
 
 ^!W^* ■L 
 
 ..y^^rV'- 
 
 
 fet>f%/.*'''' 
 
 .A 
 
 Plate X. — Upper. Illustrating a condition favorable to the 
 appearance of telegony in horses. This mare produced seven mule 
 foals and then the mare shown below. Lower. The dam of this mare 
 produced seven mule foals previous to the birth of this animal. 
 
Plate XI. — Upper. "Hallie," the eleventh foal of the dam 
 "Maude" — the latter having previously given birth to ten mule foals 
 in succession. Lower. "Maude," dam of "Hallie," produced ten 
 mule foals previous to birth of "Hallie." 
 
INHERITANCE OF ACQUIRED CHARACTERS 171 
 
 resemble a previous jack sire would be quickly observed. 
 The writer ^ and C. B. Hutchison made an investigation 
 of a large number of the horse offspring of mares which 
 had previously foaled mule progeny from jack sires. 
 Many of the horse foals examined were from mares that 
 had produced more than one mule. In one case a mare 
 had given birth to thirteen mule foals in succession and 
 had then produced a horse foal. Many similar cases 
 gave opportunity to observe a number of examples in 
 connection with which full and favorable opportunity 
 was present for the display of the influence of a previous 
 impregnation. If, as some believe, the influence of a 
 previous impregnation is cumulative and the dam becomes 
 more and more completely infected by successive matings, 
 these results should give an excellent opportunity to 
 obtain some evidence on the theory of " infection " or 
 '' saturation." 
 
 A total of 168 mares were located that had given birth 
 to mule foals and later had produced horse foals. Of 
 this number 108 produced their first foal to a jack and 
 later gave birth to horse foals. Among the number were 
 forty mares that produced their first foals to a stallion, 
 later producing mule foals and then again horse foals. 
 The remainder were bred in a somewhat irregular manner, 
 but all were alike in having produced horse foals following 
 mule foals. The number of mares producing one or more 
 mule foals each followed in every case by horse foals was 
 as follows : Eighteen males produced one mule foal each, 
 followed by a horse foal ; twenty-two mares produced 
 two mule foals each, followed by a horse foal; twelve 
 mares produced three mule foals each, followed by a 
 
 1 Mumford and Hutchison, Unpublished Data of the Missouri 
 Experiment Station. 
 
172 THE BREEDING OF ANIMALS 
 
 horse foal; twenty mares gave birth to four mule foals 
 each, followed by a horse foal; eight mares gave birth 
 to five foals each, and later to horse foals; ten mares 
 observed produced six mule foals each, and afterward 
 gave birth to horse foals; seven mares produced seven 
 mule foals followed by horse foals; G.ve mares produced 
 horse foals after having foaled eight mules each, two mares 
 dropped ten mules each, followed by horse foals; while 
 one mare produced ten mule foals and then a horse foal 
 and one mare was bred to a stallion and produced a healthy 
 horse foal after having given birth to thirteen mule foals 
 in succession. 
 
 161. Example of horse foals. — The horse foals from 
 these mares were carefully examined and measured for 
 the purpose of discovering any possible resemblances 
 to the previous jack sire from which mules had been 
 produced. The chief external characters which dis- 
 tinguish the mule from the horse are the size and form of 
 the ears, head, feet, legs, body, mane, tail, disposition and 
 voice. 
 
 The illustrations of dams and offspring give a fairly 
 adequate idea of the generally uniform nature of the 
 results which were found throughout the investigation. 
 
 In Plate X, lower, is shown the yearling offspring of a 
 mare (Plate X, upper) that had previously produced seven 
 mule foals and then gave birth to the animal shown in the 
 illustration. A careful examination of the characters in 
 which mules and horses differ showed that the offspring 
 in this case had small, rather short, smooth head, small, 
 short, pointed ears, a broad flat foot and rather broad 
 hips and loins, with a well-rounded body. None of the 
 characters of this yearling colt suggested in the slightest 
 degree any evidence that it had been influenced by the 
 
Plate X^TT tj 
 
 foals from same dam'"^i„3'''"TL*H!,°'"'J' '?!"' '""""''"e «sht -nule 
 
Plate XIII. — Upper. "Crewdson." A condition favorable to the 
 appearance of telegony. Previous to the birth of this mare her dam (Kate) 
 had given birth to eleven mule foals in succession. Lower. "Kate," 
 mother of eleven mule foals in succession, and later of "Crewdson." 
 
INHERITANCE OF ACQUIRED CHARACTERS 173 
 
 fact of its dam having previously produced seven mule 
 foals. 
 
 *' Sallie " (Plate XII, upper) was foaled by a saddle bred 
 mare fifteen years old and was the ninth foal from this 
 mare. The previous eight foals were all mules. The mare 
 " Sallie " was characterized by a small refined head of 
 good quality, a small, short and pointed ear, rather scanty 
 mane and tail, fine bone, broad and rounded foot and quiet 
 and gentle disposition. 
 
 The mare " Hallie " shown in Plate XI was sired by a 
 Standardbred stallion from the dam " Maude " (Plate XI, 
 lower). Maude had previously given birth to ten female 
 mule foals. At two years of age " Hallie " weighed 800 
 pounds, was fifteen hands high, had a short, small, refined 
 head, short pointed ears, heavy and long mane and tail, 
 broad flat foot and a rounded body. All of the external 
 characters of this mare were clearly horse characters and 
 not mule characters. There was no suggestion of any 
 resemblance to the mule in any of its characters. 
 
 '' Crewdson " (Plate XIII, upper), three years old, was 
 sired by a Hackney stallion from the dam " Kate " (Plate 
 XIII, lower), the latter having given birth to eleven mule 
 foals followed by the horse foal " Crewdson." This 
 animal was sixteen and one-half hands high and weighed 
 1000 pounds. The head was small and narrow, ear 
 short and small, mane and tail medium heavy, foot broad 
 and flat. " Crewdson " was characterized by a heavy 
 mane and tail, small ear, refined head and broad rounded 
 foot. 
 
 The cases cited and the illustrations used were selected 
 because it was assumed that if the influence of a previous 
 impregnation was likely to be exhibited at all it would 
 appear in those dams w^hich had produced a large number 
 
174 THE BREEDING OF ANIMALS 
 
 of mules followed by horse foals. No such evidence could 
 be discovered. The 168 horse offspring from mares 
 which had previously produced from one to thirteen mule 
 foals each, gave no visible evidence of the existence of 
 telegony. The external characters of the mule hybrid 
 and the horse differ so widely in many important partic- 
 ulars that even a slight influence which might come 
 through a previous sire should have been measurable. 
 
 It is true that the evidence is all negative, but it is 
 nevertheless valuable because of the peculiarly favorable 
 opportunity for the influence of telegony to assert itself. 
 It is also interesting to note in this connection that a 
 belief in the possible influence of a previous impregnation 
 is by no means universal among practical breeders, if 
 we may judge from the statements of farmers in the mule- 
 breeding districts of Missouri. Very few breeders believed 
 in the existence of telegony. Those who admitted their 
 belief in the possibility of infection were unable to cite 
 authentic instances. 
 
 162. Possibility of influence from a previous impregna- 
 tion. — If the influence of the male is not confined to 
 his immediate offspring but is extended to the mother 
 in such a way that other progeny by other males may 
 display some of the characters of the former male, then 
 such influence must come about in one of two ways. 
 The body (soma) of the mother herself may be so funda- 
 mentally changed by acquiring the characters of the male 
 that she transmits such influence to her succeeding off- 
 spring sired by other males. The spermatozoa of the 
 male may not only fertilize the fully mature and thus 
 susceptible ovum but may travel through the generative 
 organs of the female and eventually reach the ovaries 
 where the developing and immature eggs might be so 
 
INHERITANCE OF ACQUIRED CHARACTERS 175 
 
 influenced that at a later time the fully fertilized egg 
 would exhibit the results of fertilization by spermatozoa 
 from two different males. The possibility of such double 
 fertilization is extremely remote. The known facts 
 regarding the successful fertilization of the Qgg are all 
 against such an hypothesis. The ^gg is probably not 
 susceptible to fertilization by the sperm except during 
 a comparatively brief period which is coextensive with 
 the heat period in the domestic animals. The immature 
 ova still structurally a part of the ovary are not in proper 
 condition to be fertilized. The probabilities are all 
 against any such influence from this source. 
 
 Is it possible that the characters of the male may 
 become impressed upon the pregnant female through the 
 influence of the foetus ? If the body (soma) of the female 
 is influenced in this way is this influence of such a nature 
 that it can be impressed upon the embryo in the uterus ? 
 If it can, then the characters of a previous male may 
 affect the later offspring by other males. Here again we 
 must admit that the period of gestation may change the 
 body of the mother to some extent, but it is extremely 
 improbable that such change influences the offspring in 
 any hereditary sense. As Rabaud ^ says, " Gestation 
 naturally produces in the female a modification which 
 we must suppose to be to some extent permanent. As 
 a consequence, the female which produces a second off- 
 spring is no longer the female that produced the first 
 offspring; whether the two gestations be due to the 
 same male or to two different males, the foetus of the sec- 
 ond gestation evolves in conditions different from those 
 surrounding the foetus of the first gestation. But it does 
 
 1 Etienne Rabaud, "Telegony," The Journal of Heredity^ 
 vol. 5, p. 389. 
 
176 THE BREEDING OF ANIMALS 
 
 not undergo in any way the influence of the first male; 
 in reality, what takes place is as if two different females 
 were involved, mated with the same male or with two 
 different males." 
 
 The conclusion seems very plain that the practical 
 breeder has little interest in the subject of telegony. 
 While it is difficult or impossible to prove by direct 
 experiment that telegony does not exist, it is also true 
 that no one by direct experiment has ever been able to 
 produce any result which could not be explained on some 
 other basis than that of telegony. All of the supposed 
 cases of telegony can likewise be explained on some other 
 basis than the assumption that a previous impregnation 
 is lasting in its effect and may influence subsequent off- 
 spring. 
 
 163. Xenia in animals. — In plants the effect of cross- 
 pollination in certain cases is to be observed in the fruits. 
 Gardeners have long believed that the watermelons and 
 citrons should not be planted in near-by locations because 
 the pollen from the citron would injure the quality of 
 the melon. Such injury really does not occur in this 
 particular case but similar effects are present in other 
 plants. When ordinary white corn is fertilized with 
 pollen from a black variety, the grains so pollinated are 
 black or mottled while other grains on the same ear are 
 white. An explanation for this phenomenon is to be 
 found in the fact that there are two cell nuclei in the ovum 
 and two nuclei in the pollen cell. The primary nuclei 
 of the two cells unite to form the daughter nucleus of the 
 new cell. The two secondary nuclei likewise unite in 
 the formation of the endosperm. In the case of cross- 
 pollination of black and white corn it is the color of the 
 endosperm which exhibits the influence of the crossing. 
 
INHERITANCE OF ACQUIRED CHARACTERS 177 
 
 Among mammals the highly imaginative idea has been 
 suggested that the influence of the male on the female 
 (infection) may in turn be passed on to a later male mated 
 with the infected female. A highly successful breeder 
 of Shorthorn cattle in England pointed out to the author 
 a pure-bred white cow with red ears from a registered 
 sire and dam. This cow was marked like the wild white 
 cattle of Chillingham Park, and her owner ascribed her 
 markings to the fact that her dam had once dropped a 
 calf from a Chillingham bull. The cause of the peculiar 
 markings of the cow in this case could not have been 
 derived in the manner described. The case is cited here 
 only as an example of the highly improbable notion that 
 there is some relation between the phenomena of teleg- 
 ony and xenia. Xenia among mammals is unknown. 
 
 164. Xenia among poultry. — Many breeders of poultry 
 have believed that the eggs of the domestic fowl may be 
 influenced in size, form and color by the male bird. 
 Observations by Nathusius and later by Holdefleiss ^ 
 gave evidence of paternal influence on the color of the 
 eggshell. Holdefleiss mated Plymouth Rock hens with 
 a Leghorn cock. The Plymouth Rock uniformly lays 
 brown eggs while the Leghorn lays a pure white egg. 
 The eggs deposited by the Plymouth Rock hens from this 
 mating varied in color from dark brown to white. The 
 evidence seemed so clear to the investigator that he was 
 led to conclude that " The color of eggshells shows the 
 influence of the paternal strain ; there is therefore evidence 
 of xenia." More recently Walther ^ of Giessen after a 
 series of careful experiments has reported results which 
 
 1 Holdefleiss, " Berichte aus dem biologische Lab.," Univ. Halle, 
 1911. 
 
 2 Walther, "Landwirthschaftliche Jahrbiicher," 1914. 
 
 N 
 
178 THE BREEDING OF ANIMALS 
 
 do not confirm those of Nathusius and Holdefleiss. Wal- 
 ther's investigations included not only color but also 
 size, form and glossiness. His conclusions were that 
 the paternal parent has no influence on the size, shape 
 and glossiness of the eggs. His results on the color of 
 eggs are not conclusive but tend to discredit the theory 
 of xenia in fowls. From all the evidence available, it 
 would seem that the possibility of xenia in fowls is not 
 satisfactorily determined, and further investigation is 
 needed to settle this supposed influence of the male bird 
 on the color of eggs. 
 
 OBJECTIONS TO THE THEORY THAT ACQUIRED CHARACTERS 
 ARE TRANSMITTED 
 
 The trend of opinion of modern biologists has been 
 further and further away from the belief in the possibility 
 of the inheritance of acquired characters. As our knowl- 
 edge of cellular biology has increased and we have been 
 able to study the mechanical processes which are concerned 
 in reproduction and heredity, it has become more and 
 more apparent that Weismann's view of the essential 
 separateness of the soma-cells and germ-cells is sub- 
 stantially correct. 
 
 165. No mechanism for the inheritance of acquired 
 characters. — There is no mechanism by means of which 
 somatic modifications may impress themselves funda- 
 mentally upon the germ-plasm. In fact, the develop- 
 ment of the soma-cells is made possible by determiners 
 in the germ-cell. The very fact that the soma-cells 
 have been able to respond to external influences and 
 develop in a direction somewhat different from the average 
 of the species is sufficient evidence that the determiners 
 
INHERITANCE OF ACQUIRED CHARACTERS 179 
 
 which were responsible for the tendency of the organism 
 to develop in the given direction were already present 
 in the germ-plasm. As Walter aptly remarked, " Not 
 only the development of the race which we call evolution, 
 but also the determination of the individual in heredity, 
 is a chain of onward-moving sequences like the succession 
 of events in history. It is hard to see how recent events 
 can influence preceding events. It is hard to see how 
 the water that has gone over the dam can return and 
 affect the flow of the river upstream in any direct way. 
 It is likewise hard to see how differentiated somatoplasm, 
 which represents the end stage of a successive series of 
 modifications, can make any definite impress upon the 
 original germplasmal sources from which it arose." ^ 
 
 Even Darwin found difficulty in believing in the inheri- 
 tance of acquired characters. His theory of pangenesis 
 which assumed that each somatic cell added to the cir- 
 culation a minute granule which later found its way to 
 the germ-plasm is not substantiated by later investiga- 
 tions. 
 
 The evidence presented to prove that somatic modi- 
 fications are actually transmitted from parent to offspring 
 is not conclusive. It is certain that acquired characters 
 cannot be transmitted unless the germ-plasm has been 
 definitely changed by reason of somatic influence. The 
 evidence of such influence upon the germ-cell is entirely 
 negative. Definite experiments carefully planned for 
 testing the possible effect of such influence have been 
 inconclusive. 
 
 166. The inheritance of disease. — The earlier writ- 
 ings on animal breeding contain numerous references to 
 the possibility of inheritance of disease. Many examples 
 
 1 Walter, "Genetics," 1913, p. 85. 
 
180 THE BREEDING OF ANIMALS 
 
 are recorded among the domestic animals of supposed 
 cases of the heredity of pathological conditions. Among 
 the diseases which have been regarded as hereditary are 
 tuberculosis, melanosis, broken wind, specific ophthalmia, 
 blindness, spavin, ringbone, curb and many other diseases. 
 The discussion of the transmission of diseased conditions 
 of the organism brings forward again the entire question 
 of the possible inheritance of acquired characters. In 
 general it may be said that recent researches in biology 
 have resulted in demonstrating that many diseases which 
 were formerly regarded as transmissible are no longer 
 believed to be transmitted through inheritance. This 
 certainly applies to all diseases which are contracted 
 after birth. Some diseases which are the result of a 
 definite variation in the germ-plasm will of course be 
 transmitted. We must therefore clearly distinguish 
 between inborn disease and acquired disease. Certain 
 diseases or defects are undoubtedly transmitted from 
 parent to offspring. Whenever such defects represent 
 changes in the germ-plasm, then such defects will be as 
 certainly transmitted as any other character of the animal. 
 
 Such defects which may be transmitted are deaf- 
 ness, color-blindness, idiocy and possibly rheumatism, 
 gout and insanity. In the latter diseases their apparent 
 transmissibility may be the result only of a predisposition. 
 
 167. Acquired diseases. — Many diseases of the do- 
 mestic animals are acquired after birth. A large number 
 of pathological diseases are due to infection. All such 
 diseases are no more certainly transmitted than are other 
 acquired characters. Tuberculosis is the result of infec- 
 tion by a specific germ and this germ may be acquired 
 under certain conditions by the animal organism. In 
 the case of bone diseases of horses, which were for a long 
 
INHERITANCE OF ACQUIRED CHARACTERS 181 
 
 time held to be inherited, it is probable that the develop- 
 ment of such unsoundness is due largely to the action of 
 external factors. In other words, they are acquired. It 
 is true, however, that certain individual animals or 
 families are much more subject to bone disease than other 
 families. In such case we must recognize a predisposition 
 to disease. 
 
 168. Congenital disease. — The fact that a disease 
 exists at birth is not always adequate evidence that 
 disease has been inherited. It is possible for certain germ 
 diseases to infect the foetus in utero. It is also probable 
 that the ova or spermatozoa may under certain conditions 
 carry the infection and this infection may be present and 
 active during the prenatal life of the animal. 
 
 169. Predisposition to disease. — Many diseases ap- 
 pear to " run in families." For this reason we have recog- 
 nized the fact that the members of certain families are 
 subject to tuberculosis, gout, rheumatism, imbecility, 
 insanity or other diseases. In all these cases there exists 
 a predisposition on the part of the members of a given 
 family to acquire the diseased condition. Through w^eak- 
 ness of certain organs or general lack of constitutional 
 vigor, the infective germs of many diseases may overcome 
 the resistance of the animal organism to disease. This 
 predisposition is certainly and often strongly inherited. 
 From the standpoint of the practical animal breeder, 
 therefore, a predisposition to disease may be quite as 
 significant as the actual transmission of the disease. 
 
 170. Immunity. — An interesting correlated fact is 
 the probable inheritance of immunity from certain 
 diseases. Certain families seem to possess immunity 
 from certain diseases, such as smallpox or diphtheria. It 
 is not possible at this time to enter into a discussion as 
 
182 THE BREEDING OF ANIMALS 
 
 to the nature of immunity, but undoubtedly the known 
 immunity of certain individuals or families to certain 
 diseases may become the basis of important future im- 
 provements in the domestic animals. In recent years 
 it has been found that certain hogs are immune from hog 
 cholera. Experiments have been suggested to deter- 
 mine whether or not it would be possible to develop a 
 race of swine immune to this dreaded disease. 
 
 It is possible for animals to acquire immunity through 
 vaccination of actual infection of the disease itself. Such 
 immunity is not transmitted. It is doubtful whether 
 there exists any congenital immunity, but investiga- 
 tions along this line might be fruitful of results. 
 
CHAPTER IX 
 HEREDITY AND SEX 
 
 The chief function of both plants and animals is to 
 live and reproduce. In many wild forms the powers of 
 reproduction are little short of marvelous. A single 
 plant of purslane may produce a million seeds. Man is 
 less productive than most other mammals, but masses of 
 population have been known to double in twenty-five 
 years. At this rate in 1000 years there would not be 
 standing room on the earth for his children. 
 
 The natural increase of plants and animals is not real- 
 ized because of unfavorable conditions. The number 
 of animals that can exist on a given area is limited. If 
 too many are born, some must inevitably die. Others 
 are destroyed by enemies, while still others are poisoned 
 by substances which accumulate within their own bodies. 
 
 The kinds of reproduction have already been men- 
 tioned under the general subject. The simplest form of 
 reproduction is by cell division. This method of repro- 
 duction is chiefly found in unicellular organisms like the 
 amoeba and paramoecium. The most common method 
 of reproduction is by eggs. Egg production is almost 
 universal among both plants and animals. But the egg 
 generally is inert and incapable of development into a 
 new individual until it has been fertilized. Herein lies 
 the apparent reason for differentiation into male and 
 female sexes. 
 
 183 
 
184 THE BREEDING OF ANIMALS 
 
 171. The significance of conjugation and fertilization. 
 
 — The real purpose of fertilization is not well under- 
 stood. Biologists are not yet able to speak with positive 
 assurance as to the real character of the actual biological 
 phenomena which result from conjugation of the male 
 and female germ-cells. Biitschli believed that fertiliza- 
 tion was a process of rejuvenation. This idea involves 
 the assumption that the union of the germ-cells of two 
 weak individuals will result in the production of a strong 
 individual. 
 
 Jennings, in a series of very skillful and carefully con- 
 trolled experiments with paramoecium, found that after 
 conjugation the rate of division was not accelerated but 
 was actually slower. Paramoecium which had been 
 artificially weakened and their rate of division retarded 
 when allowed to conjugate was not in most cases bene- 
 fited. Some were apparently benefited, but in all cases 
 the rate of division was slower than in cultures in which 
 the paramoecium was well nourished. In other words, 
 conjugation was of advantage to some and not to others. 
 Jennings concluded that conjugation is for the purpose 
 of bringing about a recombination of characters. Some 
 of them are very beneficial and will persist and multiply, 
 others are disadvantageous and these will fail to live and 
 reproduce. The combinations most likely to persist 
 are heterozygous. 
 
 As Morgan ^ has explained, " The meaning of conjuga- 
 tion, and by implication, the meaning of fertilization in 
 the higher forms is from this point of view as follows : 
 In many forms the race, as a whole, is best maintained 
 by adapting itself to a widely varied environment. A 
 heterozygous or hybrid constitution makes this possible, 
 
 1 Morgan, "Heredity and Sex," p. 12. 
 
HEREDITY AND SEX 185 
 
 and is more likely to perpetuate itself in the long run 
 than a homozygous race that is from. the nature of the 
 case suited to a more limited range of external conditions." 
 Whatever may be the real nature and purpose of fertili- 
 zation, it is certainly true, as Wilson^ remarks, that '' the 
 paternal germ-cell is the carrier of something which 
 incites the egg to development, and thus constitutes the 
 fertilizing element in the narrower sense." 
 
 172. Secondary sexual characters. — The sexes in 
 the higher animals are differentiated, not alone by the 
 possession of radically different essential organs of repro- 
 duction, but also by the possession of so-called secondary 
 sexual characters. The more brilliant plumage of the 
 male bird, the horns of the ram, and the greater develop- 
 ment of the head and horns of the bull are examples 
 of secondary sexual characters. Darwin regarded the 
 secondary sexual characters as of great significance in 
 sexual selection. As a result of sexual selection he believed 
 that '' generally, the most vigorous males, those which 
 are best fitted for their places in nature, will leave most 
 progeny." ^ 
 
 173. Secondary sexual characters and vigor. — Breed- 
 ers of the domestic animals have long regarded the degree 
 of development of the secondary sexual characters as 
 an index of sexual vigor. Many have held that a male 
 with the secondary sexual characters strongly developed 
 was not only prepotent in the transmission of purely 
 sexual characters but also in other characters which are 
 desirable to man. Direct evidence is not available to 
 show that because an animal is strongly developed in the 
 secondary sexual characters, he is therefore prepotent 
 
 1 Wilson, "The Cell," p. 230 (1911). 
 
 2 Morgan, "Heredity and Sex," p. 101. 
 
186 THE BREEDING OF ANIMALS 
 
 in the transmission of all characters. Sexual vigor is 
 associated with the development of the secondary sexual 
 characters, and sexual vigor is a desirable character in 
 the domestic animals. The general efficiency of the 
 reproductive process is undoubtedly correlated with the 
 secondary sexual characters. The breeder, therefore, 
 is making no mistake in emphasizing the importance of 
 evidences of strong sexuality as indicated by the develop- 
 ment of the secondary sexual characters. 
 
 174. Effects of castration and ovariotomy on the 
 secondary sexual characters. — There is ample evidence 
 of the close correlation existing between the essential 
 organs of sexual reproduction and the secondary sexual 
 characters. The full development of the secondary 
 sexual characters is closely connected with sexual maturity. 
 In the Merino breed of sheep, the males are always horned 
 while the females are hornless. If the male is castrated 
 before the horns begin to develop, the horns fail to grow 
 and the wether remains hornless. If the males are 
 castrated after the horns have started to develop, the 
 horns cease to grow. Marshall, in experiments with 
 Herdwick sheep, a breed in which the males are supplied 
 with large coiled horns and the females are hornless, found 
 that castration at varying ages invariably caused a 
 cessation in the growth of the horns of the male. When 
 the ovaries of the female were removed, there was no 
 apparent tendency toward the growth of horns, although 
 small scurs appeared in one spayed ewe that was kept for 
 seventeen months after removal of the ovaries. Marshall 
 concludes, " The development of horns in the males of 
 a breed of sheep in which well-marked secondary sexual 
 differentiation occurs (as manifested especially by presence 
 or absence of horns) depends upon a stimulus arising in 
 
HEREDITY AND SEX 187 
 
 the testes, and this stimulus is essential, not merely for the 
 initiation of the horn growth, but for its continuance, the 
 horns ceasing to grow whenever the testes are removed." 
 
 " The removal of the ovaries from young ewes belong- 
 ing to such a breed does not lead to the development of 
 definitely male characters, except possibly in an extremely 
 minor degree." ^ 
 
 Arkell ^ crossed Merino ewes with a Southdown ram 
 (hornless). The sons of this cross had horns. The 
 factor for horns in this case must have been present in 
 the Merino mother, herself hornless, but the full develop- 
 ment of horns cannot take place except the male glands 
 are present and functional. 
 
 175. Effect of transplanting sexual glands. — The in- 
 vestigations already described seem clearly to point to the 
 conclusion that some stimulus to the development of the 
 secondary sexual glands exists in the testes and ovaries. 
 
 Steinach transplanted ovarian tissue from a female 
 guinea pig to the tissues of a castrated male. The result 
 was to cause the rudimentary mammary glands of the 
 male greatly to enlarge and the male came to resemble 
 the female in certain characters.^ 
 
 A remarkable experiment is described by Goodale ^ in 
 which the ovaries of a female Mallard duck were entirely 
 removed and the plumage became like that of the male 
 Mallard. 
 
 176. Effect of internal secretion. — The secretions 
 of various internal organs have a profound influence 
 upon the development of the individual. These secre- 
 
 1 Marshall, Proceedings Royal Society (London), ser. B, 85, 
 1912. 
 
 2 Arkell, New Hampshire Agr. Exp. Sta., Bui. 160. 
 
 3 Morgan, "Heredity and Sex," 1913, p. 140. 
 ^ Goodale, Journal Experimental Zoology, 10. 
 
188 THE BREEDING OF ANIMALS 
 
 tions, called '' hormones," emanate from various glands 
 and perhaps from most of the internal organs. If the 
 thyroid and parathyroid bodies are removed from the 
 body, death follows. The destruction of the pituitary 
 glands in man causes the bones of the hands, feet and jaws 
 to enlarge (gigantism), causing death. 
 
 It is probable that the milking function in the domes- 
 tic animals has some connection with the activities of a 
 specific " hormone " which is essential. 
 
 177. Sex-linked characters. — Certain characters are 
 so closely related to sex that their transmission is 
 influenced by such relation. These characters have 
 been called sex-linked or sex-limited characters. They 
 are to be distinguished from secondary sexual characters. 
 
 178. Color-blindness. — Men are much more fre- 
 quently color-blind than women. Color-blind men do 
 not transmit color-blindness directly to sons, but to grand- 
 sons through their daughters. The daughters of color- 
 blind men are not themselves color-blind, but tend to 
 transmit this deficiency to their sons. Color-blindness 
 in the daughter could be produced only when the father 
 was color-blind and the mother possessed the power to 
 transmit color-blindness. Color-blindness is the result of 
 some defect in the germ-cell. This factor which is asso- 
 ciated with an x chromosome appears twice in the ovum 
 and only once in the sperm. A similar condition is found 
 in the pomace fly ^ {Drosophila ampelophila) . This form 
 has normally red eyes, but this apparently is a unit char- 
 acter, sex-linked in transmission. An interesting case 
 of sex-linked heredity is found in the Barred Plymouth 
 Rock fowl.^ Pure barred fowls when mated produce 
 
 1 Castle, "Heredity and Eugenics," p. 75. 
 
 2 Castle, "Heredity," 1911, p. 170. 
 
HEREDITY AND SEX 189 
 
 only barred offspring. When the male Barred Rock is 
 bred with a non-barred variety, the offspring of both 
 sexes are all barred. If the female Barred Rock is mated 
 with non-barred breed, the offspring will be about one- 
 half barred and the remainder non-barred. The barred 
 offspring are always males, while all the females are non- 
 barred. The barred character is, therefore, sex-limited. 
 The Barred Rock female is heterozygous and the male 
 homozygous. The pure Barred Rock breed transmits 
 the barred quality because the male is pure in respect to 
 the barred character. The same result follows if a cross- 
 barred male is mated with barred females. The explana- 
 tion of sex-linked inheritance is probably to be found in 
 the existence of some plus element in the egg which is 
 not found in the sperm. 
 
 179. Controlling the sex of offspring. — In many of 
 the domestic animals, the sex of the individual determines 
 its peculiar value and usefulness to mankind. If some 
 method of breeding could be devised which would result 
 in the production of the particular sex desired, it would 
 be a great economic gain. That such attempts have 
 been made by both ancient and modern breeders is made 
 clear from an examination of the literature of the subject 
 from the earliest times to the present. Because of the 
 more or less general belief among practical breeders in 
 the possibility of controlling sex, it seems necessary to 
 consider briefly some of the more widely held theories of 
 sex control. 
 
 180. Age or vigor of parents. — Two investigators, 
 Sadler ^ (1830) in England and Hofaker (1823) in Ger- 
 many, collected statistics representing more than 2000 
 births. Their statistics showed that when the father is 
 
 1 Carpenter, "Human Physiology," p. 1015. 
 
190 
 
 THE BREEDING OF ANIMALS 
 
 older the larger number of the offspring are males, and 
 when the mother is older the children tend to be females. 
 These results have been confirmed by Gohlert, Boulanger 
 and Legoyt. Many practical breeders have also cited 
 special cases in which the sex offspring seemed to follow 
 that of the older parent. Giroude Buzareingues ^ reports 
 results from breeding young immature ewes to strong 
 mature rams. The proportion of sexes was 80 males 
 to 35 females. When young rams were used as sires, 
 the proportion of sexes was 53 males and 84 females. 
 
 Summary of Statistics Bearing on Relative Number 
 
 OF Males and Females ^ 
 
 
 
 
 OS ^ 
 
 J Oo 
 
 « r 
 
 
 
 
 Number 
 
 
 ^ O ^ <! 
 O i-i to s 
 
 
 §2pS 
 
 
 
 Observer 
 
 OP 
 
 Locality 
 
 «ss« 
 
 ǤS^ 
 
 bn H "^ ">J 
 
 •"^ « 32 g 
 
 ^ «< 
 
 Remarks 
 
 
 Births 
 
 
 si^^ 
 
 Sf^^w 
 
 (B O H H 
 
 oogl 
 
 
 
 
 
 
 
 Fathe 
 
 Prof 
 
 Mal 
 
 F 
 
 is 
 
 
 Hofaker 
 
 1,996 
 
 Tubingen 
 
 117.8 
 
 92.0 
 
 90.6 
 
 107.5 
 
 
 
 Sadler 
 
 2,068 
 
 England 
 
 121.4 
 
 94.8 
 
 86.5 
 
 114.7 
 
 — 
 
 Gohlert 
 
 4,584 
 
 England 
 
 108.0 
 
 93.2 
 
 82.6 
 
 105.3 
 
 — 
 
 Legoyt 
 
 52,311 
 
 Paris 
 
 104.49 
 
 102.14 
 
 97.5 
 
 102.97 
 
 — 
 
 Boulanger 
 
 6,006 
 
 Calais 
 
 109.98 
 
 107.92 
 
 101.63 
 
 107.9 
 
 — 
 
 Noirot 
 
 4,000 
 
 Dijon 
 
 99.7 
 
 — 
 
 116.0 
 
 103.5 
 
 — 
 
 Breslau 
 
 8,084 
 
 Ziirich 
 
 103.9 
 
 103.1 
 
 117.6 
 
 186.6 
 
 — 
 
 Stieda 
 
 100,590 
 
 Alsace- 
 
 
 
 
 
 
 
 
 Lorraine 
 
 105.03 
 
 — 
 
 108.39 
 
 106.27 
 
 Contra- 
 dictory 
 
 Berner 
 
 267,946 
 
 Sweden 
 
 104.61 
 
 106.23 
 
 107.45 
 
 106.0 
 
 Contra- 
 dictory 
 
 ^ Quarterly Journal of Agriculture, vol. 1, 1828, p. 63. 
 2 Geddes and Thompson, "The Evolution of Sex," p. 
 
 35. 
 
HEREDITY AND SEX 191 
 
 The differences are not large and the number of observa- 
 tions are entirely too few to justify any sweeping conclu- 
 sions. Steida ^ and Berner found no relation between 
 age and the sex of offspring. The evidence of the in- 
 fluence of age on the sex of offspring is too conflicting to 
 be conclusive. 
 
 181. Comparative vigor or sexual superiority. — Vari- 
 ous authorities have attempted to explain the proportion 
 of sexes on the theory that the sex of the offspring will 
 correspond to that of the more vigorous or '' superior " 
 parent. Darwin, Richarz, Hough and others regarded 
 the male as to a certain extent a superior organization, 
 and male offspring would result when the reproductive 
 functions of the mother were particularly well developed. 
 The evidence available is not sufficient to give this hypoth- 
 esis any particular importance in practical breeding. 
 
 182. Nutrition and sex. — That the nutritive condition 
 of the parents, particularly the mother, at the time of 
 fertilization and before has a preponderating influence 
 on the sex of offspring has been long believed. Yung 
 found that under certain conditions regarded as normal, 
 the proportion of sexes in tadpoles was about 57 females 
 to 100 males. By feeding the tadpoles beef, fish and 
 frog's flesh, the percentage of females enormously in- 
 creased, being in one case 92 females to 8 males. An 
 interesting case illustrating the connection of nutrition 
 and sex is found in bees. The swarm of bees is composed 
 of workers (imperfect females), drones (males) and the 
 queen (a perfect female). The drones are hatched from 
 unfertilized eggs. The queen and workers are developed 
 from fertilized eggs, but perform a very different role in 
 life. The queen becomes the mother of new generations, 
 
 1 Ihid. 
 
192 THE BREEDING OF ANIMALS 
 
 while the worker bees are sexually imperfect. It seems 
 to be true that the eggs developing into worker bees 
 and queens are identical. The one becomes a queen as 
 the result of a '' royal " diet, while the worker larvae 
 are fed on a " common " diet and develop into the non- 
 fertile female. Investigations with wasps by Von Siebold ^ 
 and butterflies and moths by Mrs. Treat suggest a real 
 connection between nutrition and sex offspring. Schenk 
 found that starvation produced fewer males, but later 
 the same condition resulted in producing more males. 
 Diising reported that among the Swedish nobility the 
 proportion of sexes was 98 boys to 100 girls, and in the 
 Swedish clergy 108.6 boys to 100 girls. Punnett submits 
 evidence that in London more girls are born among the 
 poor than the rich. In most of the cases cited there are 
 too many other factors involved to justify the conclusion 
 that nutrition alone is responsible for the proportion of 
 the sexes. 
 
 183. The maturity of the ovum. — The degree of 
 development or maturity of the ovum itself at the time 
 of fertilization has a controlling influence on sex in the 
 opinion of some breeders. If fertilization occurs during 
 the early part of the heat, the offspring will be female. 
 If the ovum is fertilized later in the heat, the offspring 
 will tend to be males. Thus Thury ^ of Geneva says, 
 " The sex depends upon the degree of maturity of the 
 egg at the moment of fecundation, that which has not 
 reached a certain degree of maturity producing the female, 
 and, if fecundated when this point of maturity has passed, 
 producing a male." These results are not altogether 
 consistent with ordinary farm practice or with the experi- 
 
 1 Rolph, W. H., "Biologische Probleme," Leipsig, 1884. 
 
 2 Country Gentleman, 1864, p. 12. 
 
HEREDITY AND SEX 193 
 
 ments of others. In ordinary breeding operations on the 
 range, the bull invariably runs with the cows and breed- 
 ing occurs during the first part of the heat. If the sex 
 is determined to any extent by the particular stage of 
 heat, then in this case the offspring should be largely 
 female. But such is not the case, the proportion of the 
 sexes is practically equal, subject to seasonal or other 
 variations not entirely explainable. Thury's results 
 have not been satisfactorily confirmed. Miles ^ recorded 
 the proportion of sexes among cattle and sheep on the 
 Michigan Agricultural College farm for a period of ten 
 years. The results were as follows : Sheep, 102.5 males 
 to 100 females. Cattle, 118.4 males to 100 females. All 
 the animals were bred during the first part of the heat 
 and the offspring should have been more largely female. 
 The proportion of the sexes seems to be subject to wide 
 variation, and therefore any investigations of this kind 
 must necessarily include large numbers of animals and 
 the observation be carried over a series of years to make 
 the results of any value. 
 
 184. Seasonal variations in proportion of sexes. — 
 The proportion of the sexes is subject to wide variations 
 apparently due to seasonal influences. Quoting again 
 from Miles : ^ 
 
 " In 1864 and 1865 the bull-calves were 2.5 to 1 heifer ; 
 in 1866 and 1867 the heifers were considerably in excess ; 
 in 1868 and 1869 the heifers were nearly 2 to 1 bulls ; in 
 
 1870 the bulls were decidedly more numerous ; and in 
 
 1871 and 1872 there were more than 2 bulls to 1 heifer. 
 In 1872 there were 2 rams to 1 ewe, and the bulls were 
 nearly in the same proportion to the heifers, which would 
 
 1 Miles, "Stock Breeding," 1878, p. 265. 
 
 2 Ibid., p. 299. 
 o 
 
194 THE BREEDING OF ANIMALS 
 
 seem to indicate some peculiar influence of the season in 
 favor of the males. In 1871, however, the bulls were 
 largely in excess of the cow-calves, and there was quite 
 as decided a preponderance of females among the sheep." 
 
 185. Sex cannot be controlled by external conditions. 
 — The most recent investigations of sex determination 
 lead to the belief that sex is predetermined in the germ- 
 cell. It is not subject to change through any change in 
 the environment, as nutrition or temperature. The 
 germ-cell contains a determiner for sex as it contains 
 determiners for other characters. 
 
 Castle concludes, ^ ''If, as has been suggested, the deter- 
 mination of sex in general depends upon the inheritance 
 of a Mendelian factor differentiating the sexes, it is highly 
 improbable that the breeder will ever be able to control 
 sex. Male and female zygotes should forever continue 
 to be produced in approximate equality, and consistent 
 inequality of male and female births could result only from 
 greater mortality on the part of one sort of zygote than 
 of the other." 
 
 The same idea is similarly expounded by Morgan.^ 
 " If these observations are confirmed, they show that 
 in man, as in so many other animals, an internal mechan- 
 ism exists by which sex is determined. It is futile, then, 
 to search for environmental changes that might determine 
 sex. At best the environment may slightly disturb the 
 regular working out of the two possible combinations 
 that give male or female. Such disturbances may affect 
 the sex ratio but have nothing to do with sex-determina- 
 tion. 
 
 1 Castle, "Heredity," 1911, p. 180. 
 
 2 Morgan, "Heredity and Sex," p. 248. 
 
CHAPTER X 
 VARIATION 
 
 No biological fact is more clearly recognized than the 
 tendency of all plants and animals to vary. In a broad 
 way, individuals resemble their parents. Through hered- 
 ity the qualities of the parent are transmitted to the off- 
 spring. A horse begets other horses and not pigs. We 
 do not gather grapes of thorns nor figs from thistles. 
 Thus has come about the old adage " like begets like," 
 but this aphorism applies only within certain limits and 
 fails to take into account the inexorable law of variation 
 by which the offspring is never exactly like the parent. 
 It is true that the offspring of a horse will always be a 
 horse and not a cow. It is even true that the progeny of 
 a trotting horse will be a trotting horse, but the keen 
 judge of horses is able to discern slight variations in form, 
 color, disposition or ability to perform. 
 
 No two animals are exactly alike. The difference 
 may be slight or very marked. From the same sire and 
 dam, the offspring may differ widely in character among 
 themselves. In a large family of boys, the physical 
 characters and mental dispositions of the individual 
 members of the family may be very different. It has 
 happened in the history of trotting and running horses 
 that own brothers have varied widely in their ability 
 to win in speed competitions. 
 
 195 
 
196 THE BREEDING OF ANIMALS 
 
 186. Importance of variability. — The inherent tend- 
 ency to vary which exists in all organic beings makes the 
 improvement of domestic races possible. Inorganic 
 compomids are fixed in composition and physical char- 
 acter. Pure gold cannot be improved. The individual 
 animal has within its own organic constitution not only 
 the capacity for, but a noticeable tendency toward, varia- 
 tion from the characters of its ancestors. This fact lies 
 at the very foundation of the successful improvement 
 of domestic animals. If it were true that the offspring 
 was identical in character with the parent, then improve- 
 ment would be impossible. 
 
 In developing new varieties, the breeders' efforts 
 are sometimes first directed toward encouraging the 
 tendency to variation. If the particular form which 
 the breeder is endeavoring to improve possesses an unusual 
 tendency to vary, then a large number of new characters 
 or new combinations of characters will occur. Some of 
 these will be desirable, but many will be less desirable 
 than in the parent forms. The individuals which possess 
 the most useful and valuable characteristics will be pre- 
 served by selection. After desirable variations have 
 occurred, the next step is to fix these by heredity so that 
 they may become racial characteristics and be trans- 
 mitted with some degree of regularity from parent to 
 offspring. 
 
 187. Morphological variations. — The variations which 
 are of interest to the animal-breeder exhibit many differ- 
 ent forms. 
 
 Morphological variations are those affecting the form. 
 These may be merely differences in size, as in the case 
 of two pigs possessing the same characters and the same 
 relative development of characters but differing in size. 
 
VARIATION 197 
 
 Some individuals are dwarfs while others are giants in 
 size. This variation in size is due to a difference in the 
 number of cells rather than in the size of the cells. The 
 increased number of cells found in the larger individuals 
 represents excessive cell division, while the abnormally 
 small are the result of imperfect and arrested cell division.^ 
 
 The cause of undersized individuals among animals 
 cannot always be determined. It is certain, however, 
 that insufficient food or food which is deficient in the 
 necessary elements of nutrition is a common cause of 
 undersized animals. 
 
 It is also true that when females become pregnant 
 while still growing and immature, their growth receives 
 a sudden check. The arrested development is not so 
 much due to the effects of pregnancy as to the strain of 
 lactation. The growth of well-fed females is probably 
 not to any appreciable extent checked by pregnancy, 
 but the physiological requirements for the production 
 of milk are severe and the development of immature 
 mammalian females is abruptly arrested during the 
 period of lactation. 
 
 DiflPerences in size are of relatively less importance than 
 morphological differences arising from variation in the 
 relative development of the parts of the body. This 
 may be illustrated by the variations in meat animals. 
 Beef cattle may possess a broad back, well-sprung rib, 
 and a thick covering of flesh over all parts, or they may 
 lack these highly desirable qualities. 
 
 188. Physiological variations. — Changes in the func- 
 tional activities of animals are frequent and important. 
 The average domestic cow produces not more than 150 
 pounds of butter in a year, but selected herds may produce 
 
 ^ Davenport, "Principles of Breeding," p. 27. 
 
198 THE BREEDING OF ANIMALS^ 
 
 500 pounds of butter in one year. Some individuals 
 are very fertile, others may be sterile or markedly deficient 
 in this very desirable quality. 
 
 189. Meristic variation. — All plants or animals develop 
 in accordance with a certain symmetrical pattern. A 
 quadruped has four legs, two ears, two eyes, and two sides 
 of similar character. A deviation from the characteristic 
 plan or pattern of the species is called a meristic variation. 
 Such variations are of very great importance among 
 plants, but are of little practical significance to the animal- 
 breeder. Examples of meristic variation are to be seen 
 in the doubling of flowers, the stooling of grains, and 
 the production of four-leaved clovers. Among animals 
 the growth of extra fingers and toes, and the development 
 of an abnormal number of vertebrae or ribs, are not un- 
 common. An interesting example of this type of varia- 
 tion is found in the development of extra mammae. 
 Supernumerary nipples in mammals are a common form 
 of variation among humans. Bruce ^ found fourteen 
 cases of extra mammae among 2311 females examined. 
 Most male mammals are supplied with rudimentary 
 nipples, and curiously there seems a greater amount of 
 variation among males than females. The same authority 
 quoted above found forty-seven cases of multiple nipples 
 among 1645 males examined. In one case a woman ^ 
 is reported to have possessed five pairs of nipples. The 
 presence of a larger number of mammae than the normal 
 has been regarded by some as evidence of greater fertility.^ 
 A variation in the opposite direction resulting in the 
 development of a smaller number of digits than the normal 
 
 1 Bateson, "Materials for the Study of Variation." 
 
 2 Ibid., p. 183. 
 
 3 Bell, "Multinippled Sheep." 
 
VARIATION 199 
 
 is to be found in the case of the " mule-footed " hog. In 
 this instance, the spht hoof has united into one soUd 
 hoof Hke the horse, and this variation is strongly inherited. 
 Meristic variations are often transmitted by heredity. 
 
 190. Functional variations. — In our discussion of 
 variation up to this point, we have chiefly concerned 
 ourselves with such changes as are exhibited in the form 
 of animals. We have now to consider those important 
 modifications which affect the performance of the indi- 
 vidual. An animal may retain the same form as the 
 average of the race but be vastly more efficient in the 
 performance of some one or more of the physiological 
 functions. This type of variation is one of the most 
 important to the animal-breeder. The value of many of 
 the domestic animals depends entirely upon their func- 
 tional development. The chief advantage possessed by 
 some domesticated animals over their wild progenitors 
 is due to their higher functional efficiency. This is illus- 
 trated by the domestic coav, the improved breeds of wool 
 sheep, and the trotting horse. Such differences in form 
 between the wild and domestic sorts as are present are 
 chiefly significant as indicating the correlation which exists 
 between function and form. The changed form, if it ex- 
 ists, is incidental and the result of functional influence. 
 
 The valuable variation which the breeder has em- 
 phasized in his selection has been the ability of the animal 
 to produce economically and largely some valued animal 
 product. The breeder did not in the beginning consciously 
 select variations in form. It is true, however, that the 
 efficient performance of animals is to a certain extent 
 correlated with the form, and it follows, therefore, that 
 we may within certain rather narrow limits rely upon 
 the external form as an indication of functional efficiency. 
 
200 THE BREEDING OF ANIMALS 
 
 191. Examples of functional variation. — In most cases 
 the functional variations in the domestic animals which 
 have become valuable to man are modifications of natural 
 functions possessed by all wild animals living under nat- 
 ural conditions. The present stage of development in 
 domestic forms is due to artificial selection practiced by 
 man. The variations which have been desirable have 
 been preserved through selection and a gradual improve- 
 ment in functional efficiency has resulted. These varia- 
 tions may arise through sudden mutations, but such 
 marked changes in function are probably less common 
 than similar mutations in form. Variations in the func- 
 tional activities of animals are of great economic impor- 
 tance to the breeder of domestic animals. It is important 
 to know with some degree of definiteness the extent of 
 variation in function, as such knowledge will give some 
 idea of the probable limits of improvement. The follow- 
 ing examples of functional variation will be useful in 
 helping to determine the limitations of improvement. 
 Such examples may be greatly multiplied by search of 
 the literature of the subject. 
 
 192. Variation in fertility of animals. — It is well 
 known that there are wide differences among individual 
 animals and among races or breeds in their ability to 
 produce large numbers of offspring. The quality of 
 fertility is one of great practical importance and is readily 
 transmitted by heredity. Miles ^ has recorded the case 
 of a cow belonging to a French farmer which produced 
 nine calves at three births, four at the first, three at the 
 second, and two at the third. ^ A Teeswater ewe belonging 
 to Edward Eddison produced four lambs in 1772 when 
 
 1 Miles, "Stock Breeding," p. 131. 
 
 2 "British Husbandry," vol. II, p. 438. 
 
VARIATION 201 
 
 two years old ; " in 1773, five ; in 1774, two ; in 1775, 
 five; in 1776, two; and in 1777, two. The first nine 
 lambs were lambed within eleven months." ^ The 
 Country Gentleman reports the case of a sow that 
 produced twenty-three pigs at one birth. The above 
 examples are of unusual cases of fertility and are so far 
 above the average fertility of the respective races of 
 animals that they represent a marked departure from 
 the established type. Other things being equal, those 
 races of domestic animals which are most fertile are most 
 profitable. One of the qualities of economic importance 
 which commends certain breeds to the practical farmer 
 is the quality of fertility. This is especially true among 
 swine and sheep. 
 
 193. Variation in the milking function. — The milk- 
 ing function in domesticated animals is of special interest 
 for the reason that it is probably the most valuable single 
 functional variation in the domestic animals. The im- 
 provement of the domestic cow in the direction of greater 
 functional efficiency in the production of milk and butter 
 has been little short of marvelous. This improvement 
 has not only resulted in developing an animal with a 
 capacity to produce enormous quantities of milk, but the 
 efficiency of the cow in the economic utilization of food 
 has been no less noteworthy. The highly improved 
 domestic cow is able to utilize the raw products of the 
 farm, consisting of grain, hay and grass, and produce 
 from these a larger amount of human food than any other 
 domestic animal. The high efficiency of the milk cow 
 as compared with the beef steer is clearly shown by the 
 records kept at the Missouri Experiment Station.^ A 
 
 1 CuUey, "Live Stock," p. 123. 
 
 2 Eckles, ''Dairy Cattle," p. 6. 
 
202 THE BREEDING OF ANIMALS 
 
 Holstein Friesian cow produced 18,405 pounds of milk 
 in one year. This year's production from one cow con- 
 tained 2218 pounds of dry matter. At the same station, 
 the carcass of a 1250-pound fat steer was analyzed. The 
 steer was twenty-one months old and had been fed gen- 
 erously from birth. The steer's carcass contained 548 
 pounds of dry matter, or a little less than one-fourth the 
 amount of dry matter produced by the cow in one year. 
 The dry matter recorded for the steer was for the entire 
 carcass of the animal, including hide, horns, bones and 
 intestines. The actual net weight of the dry matter of 
 the edible portion of the fat animal was only 357 pounds. 
 In other words, the Holstein Friesian cow produced six 
 times as much edible human food in twelve months as 
 was produced by the fattening and growing steer in 
 twenty-one months. In the case just cited, it is true 
 that the cow was far above the average in efficiency while 
 the steer was a fair representative of a good average beef 
 animal. The example is nevertheless a most excellent il- 
 lustration of the very great development and improvement 
 of the dairy cow in the direction of desirable variations. 
 The foregoing records of the two animals did not include 
 the dry matter consumed in the production of milk and 
 beef. Such a record which would give the amount of 
 dry matter required to produce a pound of dry matter in 
 milk as compared with a pound of dry matter in beef 
 would be of great interest. Such records have been kept 
 at a number of American experiment stations. 
 
 The feed and milk record of Pedro's Ramaposa 181,160 
 has been given by Eckles,^ and from this the dry matter 
 in feed which is required to produce a pound of dry matter 
 
 ^ Eckles, Missouri Experiment Station, Research Bulletin, No. 
 2, p. 117. 
 
VARIATION 203 
 
 in milk can easily be determined. The cow, Pedro's 
 Ramaposa, during a period of one year produced 8522.9 
 pounds of milk which contained 1317 pounds of dry 
 matter. In the production of this quantity of milk she 
 consumed in feed 9362 pounds of dry matter. In other 
 words, the consumption of 100 pounds of dry matter 
 in the feed resulted in the production of 91.12 pounds of 
 milk containing 14.06 pounds of dry matter. Stated 
 in other terms, the cow here described produced one pound 
 of dry matter in the milk for each 7.1 pounds of dry 
 matter consumed in the feed. i 
 
 194. Variations among different cows. — The milking 
 function is hereditary and is a comparatively well-fixed 
 character among the dairy breeds of cattle. It is true, 
 however, that there still exist wide variations in the 
 productive capacity of cows, even of the same breeding 
 as well as those of different ancestry. The Illinois 
 Experiment Station ^ in several tests has clearly demon- 
 strated the wide differences which may exist between 
 individuals.^ Two native cows. Rose, nine years old, 
 and Nora, six years old, were fed the same kind of 
 a ration for twelve months. The amount fed was de- 
 termined by the appetites of the animals. The table 
 on the following page gives the essential facts of interest 
 in this connection. 
 
 " Reduced to a like feed basis, for every 100 lb. of milk 
 given by Nora, Rose gave 139.5 lb., and for every 
 100 lb. of butter-fat produced by Nora, Rose produced 
 180.7 lb." 
 
 Commenting on this test, Fraser says,^ " As milk is 
 
 1 Fraser, Illinois Experiment Station, Bulletins 51 and 66. 
 
 2 Davenport, "Principles of Breeding," p. 78. 
 ' Loc. cit. 
 
204 
 
 THE BREEDING OF ANIMALS 
 
 nearly always valued by the amount of butter-fat which 
 it contains, and Rose produced on the same feed basis 
 1.807 times as much butter-fat as Nora, the difference in 
 yield between the two cows was 252.27 lb. of butter-fat 
 or 294.31 lb. of butter per year. This at 16 cents per 
 pound, which is the average value of butter before being 
 made up, would amount to $47.09 per year. Supposing 
 that the cows would yield in this ratio for six years, 
 from the age of four to ten, which is a conservative 
 estimate, Rose would produce $282.54 worth of butter 
 more than Nora on exactly the same kind and quantity 
 of feed ; 
 
 Record of the Two Cows for One Year Computed on 
 
 A Like Feed Basis 
 
 Reduced to a like feed basis the 
 amount Nora would have pro- 
 duced had she eaten the same 
 as Rose : 
 
 Total digestible dry matter con- 
 sumed in pounds 
 
 Total yield of milk, in pounds . 
 
 Total yield of butter-fat, in 
 pounds 
 
 Total yield of butter, in pounds 
 
 Total value of butter at 16 ji per 
 pound. . . , 
 
 Rose 
 
 6477.92 
 11,329.00 
 
 564.80 
 658.90 
 
 $105.43 
 
 Nora 
 
 6477.92 
 8121.60 
 
 312.53 
 364.62 
 
 $58.34 
 
 Difference 
 
 3207.40 
 
 252.27 
 
 294.28 
 
 $47.09 
 
 " In this comparison Rose was at a disadvantage in 
 two ways. She was nine years of age and on the down 
 grade of life while Nora was just in her prime. Rose was 
 bred November 5, 1899, while Nora was not bred until 
 
VARIATION 205 
 
 after the experiment closed. Had it not been for these 
 two hindrances Rose would doubtless have made even a 
 better record than she did. 
 
 " While there is a vast difference in the profit derived 
 from the two cows in this experiment, the difference is 
 by no means phenomenal, as greater differences than 
 here cited may frequently be found among cows in the 
 same herd, for the cow Nora, the poorer of the two, was 
 in reality an exceptionally good cow, producing 348 lb. 
 of butter in a year which is nearly three times the average 
 yield (130 lb.) of cows in the United States and almost 
 one-half more than the average yield (250 lb.) of profitable 
 cows in Illinois. Had Rose been compared with a really 
 poor cow, such as may be found in nearly all dairy herds, 
 there would have been a much greater difference in profit 
 in favor of Rose ; for she gave nearly five times as much 
 as a profitable cow for Illinois." 
 
 In the cases of variation mentioned, the individuals 
 compared have belonged to different breed-s or have been 
 unrelated. It is also true that animals which are from 
 parents of the same blood lines may show wide variations. 
 In the dairy herd belonging to the University of Missouri, 
 there were at one time nineteen daughters of the Jersey 
 bull Minette's Pedro. Many of the mothers of these 
 cows were from another bull and all were of similar breed- 
 ing. The conditions surrounding these cows were alike; 
 their dams, grand dams, and great grand dams were all 
 similarly bred and every cow of the nineteen was sired 
 by Minette's Pedro. These cows should have exhibited 
 some uniformity in the development of dairy qualities. 
 The table records the annual production of milk and 
 butter, and shows rather wide variations in the productive 
 capacity of the different cows : 
 
206 
 
 THE BREEDING OF ANIMALS 
 
 Records of the Daughters of Minette's Pedro ^ 
 
 
 Number 
 
 Lactation 
 
 Periods 
 
 Average 
 Lbs. Milk 
 
 Average 
 Lbs. Fat 
 
 Pedro's Ramaposa 
 
 3 
 
 6750 
 
 365.8 
 
 Pedro's Elf ... . 
 
 
 3 
 
 2225 
 
 109.4 
 
 Pedro's Alphea Elf . 
 
 
 5 
 
 6151 
 
 309.8 
 
 University May . . 
 
 
 3 
 
 4723 
 
 227.0 
 
 Columbia Huguita 
 
 
 5 
 
 6322 
 
 273.1 
 
 Pedro's Daisy Bate . 
 
 
 2 
 
 3456 
 
 193.7 
 
 Missouri Daizie 
 
 
 1 
 
 4910 
 
 205.5 
 
 University Daizie . 
 
 
 4 
 
 7746 
 
 405.6 
 
 University Stella . . 
 
 
 3 
 
 5336 
 
 273.7 
 
 University Elf . . 
 
 
 4 
 
 5053 
 
 247.3 
 
 University Belle . 
 
 
 3 
 
 4960 
 
 223.8 
 
 Pedro's Grace Briggs 
 
 
 3 
 
 4909 
 
 287.9 
 
 Pedro's Matron 
 
 
 3 
 
 6582 
 
 355.9 
 
 Miss Missouri .... 
 
 
 3 
 
 6844 
 
 331.0 
 
 Pedro's Emily Harris 
 
 
 3 
 
 5271 
 
 238.5 
 
 Pedro's Estella . . . 
 
 
 2 
 
 8807 
 
 462.1 
 
 Pedro's Alphea Ward 
 
 
 1 
 
 4728 
 
 267.0 
 
 Pedro's May Hubbard . 
 
 
 4 
 
 4073 
 
 184.9 
 
 Pedro's Virginia Meredith . 
 
 3 
 
 5776 
 
 320.6 
 
 195. New characters originate in the germ-plasm. — 
 In the preceding discussion of the possibiUty of the 
 inheritance of acquired characters, we have followed 
 closely Weismann's definition of acquired characters. It 
 must be admitted, however, that in the discussion of 
 this subject by many students of heredity, the use of 
 the term has not been confined strictly to Weismann's 
 interpretation. Many biologists would include under 
 the discussion of this subject all acquired characters, 
 regardless of whether they may have originated through 
 
 1 Eekles, Missouri Experiment Station, Research Bulletin, 
 No. 2, p. 108. 
 
VARIATION 207 
 
 environmental influences acting upon the soma-cells or 
 from variations directly affecting the germ-plasm itself. 
 
 Many new characters appearing in plants and animals 
 cannot be traced to environmental influences acting upon 
 the soma-cells. Many characters seem to arise inde- 
 pendently of external causes. They undoubtedly have 
 their origin in the germ-plasm itself. Such variations 
 are fundamentally different from the characters which 
 are acquired by the soma-cells as the result of environment, 
 use or disuse, disease and mutilations. 
 
 The germ-cell which contains within its own substance 
 the materials needed for giving direction to the develop- 
 ment of the new individual is the result of the union of 
 two other germ-cells from individuals which may repre- 
 sent widely different characters. It is impossible that 
 the new individual arising from such a germ-cell shall 
 possess characters identical with either parent. The 
 offspring represents a certain amount of variation which 
 had its origin in the germ-cell itself. 
 
 The mechanism of reproduction, including the matura- 
 tion and reduction of the germ-cells and the union of the 
 chromosomes, provides ample opportunity for new com- 
 binations of characters which may profoundly change 
 the whole physiological history of the offspring. 
 
 196. Mutilations. — Many examples of mutilations 
 and their supposed transmission from parent to offspring 
 have given to advocates of the belief in the transmission 
 of acquired characters many of their most interesting 
 examples. Various investigators have cut off the tails 
 of mice for many generations with a view to investigating 
 the result of such mutilation upon its transmissibility. 
 Cope, Mantegazza and Rosenthal cut off the tails of mice 
 for eleven generations. Bos for fifteen, and Weismann 
 
208 THE BREEDING OF ANIMALS 
 
 for nineteen generations, but in no single case was there 
 the sHghtest evidence that this form of mutilation was 
 transmitted. 
 
 The tails of sheep have been cut off for many hundred 
 years by shepherds, but tails reappear regularly with the 
 normal number of vertebrse and without diminution in 
 length. 
 
 A large number of examples have been given of cats 
 whose tails have been removed and who have later trans- 
 mitted to their offspring a tendency to short tails. In 
 the Eiffel, the peasants shorten the tails of cats. It is 
 reported by Tietz that cats with defective tails are common 
 in this region. Many similar examples are reported. In 
 this and most other examples of the inheritance of acquired 
 characters, there is no evidence that the artificial shorten- 
 ing of the tails is the direct cause of the atrophied tails 
 observed in the kittens. Such defective tails are not 
 uncommon in races of cats with normal tails. It must 
 also be remembered that there are tailless breeds of cats 
 such as the Manx and Japanese breeds, and the admixture 
 of such breeds might be sufficient to explain the observed 
 variations. 
 
 The cattlemen of the Nile Valley have for an unknown 
 period of time caused the horns of cattle to grow in curi- 
 ous spiral forms, but there is no evidence that such 
 deformities are transmitted to the offspring.^ 
 
 197. The Brown-Sequard experiments,^ — The most 
 frequently quoted and credible scientific experiment 
 conducted for the purpose of causing somatic modifica- 
 tions and observing their transmission from parent to 
 
 1 Hartman, "Die Haussaugethiere der Wildlander," Ann. 
 Landwirthsch., Berlin, 1864, p. 28. 
 
 2 Romanes, "Darwin and after Darwin," vol. II, chap. IV. 
 
VARIATION 209 
 
 offspring are the famous Brown-Sequard experiments 
 with guinea pigs. From 1869 to 1891, Brown-Sequard 
 cut the sciatic nerve of the leg or the spinal cord in the 
 dorsal region, causing an abnormal nervous condition 
 resembling the symptoms of epilepsy. These animals when 
 allowed to breed produced offspring, many of which were 
 epileptic like the parents. Similar results were later 
 secured by Westphal, Dupuy, Obersteiner and Romanes. 
 This interesting investigation has been promptly accepted 
 by the special advocates of the transmission of acquired 
 characters as fulfilling the oft repeated demand for direct 
 evidence of the inheritance of somatic modifications. 
 
 In discussing the results it must not be forgotten that 
 the mutilation was never transmitted, but only the epilep- 
 tic state resulting from the mutilation. The results from 
 this type of mutilation were very diverse. According to 
 Romanes, the epileptic condition was rarely transmitted. 
 Brown-Sequard admitted that certain particular results 
 were exhibited in only one or two per cent of cases. If 
 this mutilation had actually influenced the germ-plasm 
 in such a way as to add to its fundamental constitution 
 the determiners essential for the development of the new 
 characters, then surely we might expect a larger part of 
 the offspring to be affected with the acquired character. 
 
 Max Sommer in 1900 repeated the Brown-Sequard 
 experiments, but failed to confirm the conclusion that 
 this experiment had proven the existence of acquired 
 characters. " As regards the hereditary transmission of 
 epilepsy in guinea pigs," says Sommer, "or of other 
 accidentally acquired pathological symptoms — e.g. de- 
 fects in the toes — we have not been able to confirm 
 the experiments of Brown-Sequard and Obersteiner; 
 and we do not think that these can any longer serve as 
 
210 THE BREEDING OF ANIMALS 
 
 a support to the doctrine of the inheritance of acquired 
 characters." ^ 
 
 198. Causes of variation. — The nature of variation 
 is still obscure. The fundamental causes are not easily 
 determined. " Our ignorance of the laws of variation 
 is profound/' says Dgj'win. 
 
 The results of the investigations in cytology have given 
 a more reasonable basis for understanding the subject 
 of variation, but it has not yet given us a wholly satis- 
 factory knowledge of the causes of variation. Bateson 
 holds that we are yet far from a satisfactory explanation 
 of the real nature of variation. He has concluded that 
 '' Inquiry into the causes of variation is, in my judgment, 
 premature." We are, however, able to recognize and 
 classify certain apparent causes of variation. Such clas- 
 sification recognizes causes of variation as external and 
 internal. 
 
 Davenport ^ has further classified the internal causes 
 of variation as: ''1. Internal influences affecting pri- 
 marily the individual, and 2. internal influences affecting 
 the race as a whole." 
 
 199. Cell division a cause of variation. — Every animal 
 is the product of the union of the germ substance of two 
 other animals. The union of the germ-cells is a union 
 of the characters of the parents. This combination of 
 the germinal matter of the two parents results in a rear- 
 rangement of some of the characters, and these may vary 
 materially from the original characters of the parents. 
 Weismann calls this mixing of the germ-plasm amphimixis. 
 He is of the opinion that sexual reproduction by cell union 
 and cell division is nature's plan for increasing variation. 
 
 1 Thomson, " Heredity," pp. 230-236. 
 
 - Davenport, "Principles of Breeding," p. 155. 
 
VARIATION 211 
 
 New characters may arise or old ones be lost through 
 accidents to the germ substance during the processes of 
 cell division incident to reproduction and growth. It is 
 conceivable that a chromosome bearing within its ma- 
 terial substance a character or set of characters may be 
 lost or destroyed at some stage of the complicated pro- 
 cesses which eventually result in the formation of a new 
 germ-cell. If such a thing occurs, it must influence 
 greatly the ultimate characters of the individual. It is 
 also apparent that a fundamental change in the germinal 
 material may influence not alone the resulting individual 
 but the race or breed. Sudden marked variations may 
 and do often occur, and these may become the beginnings 
 of new races. These sudden variations are called muta- 
 tions by De Vries, and the mutation theory of evolution 
 is regarded as one of the most important advances since 
 Darwin. A fuller discussion of mutations will be found 
 on another page. 
 
 It is difficult to differentiate between those variations 
 which are merely the result of the action of environment 
 on the soma- or body-cells and those variations which 
 are the result of a fundamental change in the constitu- 
 tion of the germ substance. The former are generally 
 temporary and affect only the individual, but do not 
 influence the germ sufficiently to cause the same varia- 
 tion to appear in the offspring. The highly improved 
 types of domestic swine if permitted to run wild in the 
 woods lose their rounded full-fleshed form and assume 
 much the appearance of the unimproved " razor-back.'* 
 Their appearance is so changed by this treatment that 
 the most skillful judge of swine would be greatly deceived. 
 The ^' razor-back," on the other hand, has subsisted for 
 generations upon the mast of the forest. This has in- 
 
212 THE BREEDING OF ANIMALS 
 
 volved much exercise and the ability to Hve on a scant 
 supply of food at certain seasons. These conditions have 
 resulted in changing the form of the body. The neck 
 and jaws are larger and well muscled. The back is sharp, 
 legs longer and ribs flatter than in the improved forms. 
 If the young pigs of these unimproved swine are placed 
 under conditions where they are supplied with an abun- 
 dance of nutritious food, they approach somewhat the well- 
 rounded form of the improved type. In each of these 
 cases the environment has resulted in causing a distinct 
 variation from the parent form. This variation can be 
 easily observed, it can be measured. But whether this 
 environment has influenced in any way or how much it 
 has influenced the elemental carriers of heredity in the 
 germ, it is impossible to do more than conjecture. It 
 cannot be accurately measured. Biologists are generally 
 agreed that in a case of this kind the germ is not funda- 
 mentally changed. 
 
 200. Influence of use and disuse in causing modifica- 
 tions. — The constant use of an organ in the performance 
 of work will modify the organ in accordance with the work 
 performed. Any organ of the body that is not used may 
 atrophy. Changes resulting from excessive use of the 
 various parts of the body may be so extensive as to appear 
 almost as new characters. If modifications resulting 
 from food, climate or mutilations are transmitted, the 
 changes resulting from the constant use of an organ should 
 be transmitted with equal or greater force. 
 
 Lamarck's theory of evolution was largely based upon 
 the supposed adaptation of the various organs of the 
 body to their environment, and that such adaptations 
 were readily transmitted. Thus the giraffe, forced by 
 conditions to feed upon the leaves of trees, gradually 
 
VARIATION 213 
 
 extended his neck, which became longer, and this increase 
 in length was transmitted from generation to generation. 
 Wading birds, feeding in the shallow water along the shore, 
 gradually waded deeper and deeper into the water. 
 Their legs became longer, and the additional length gained 
 by each generation was transmitted. The long tongue 
 of the ant-eater, of woodpeckers, and humming birds, 
 was developed . in a similar manner. The rudimentary 
 eyes of subterranean animals and fish in caves is another 
 supposed example of the loss of an organ through disuse. 
 
 Among domestic animals, there are numerous examples 
 of a high degree of development of organs through con- 
 tinued exercise. The milking function in the dairy cow 
 can undoubtedly be greatly improved in any individual 
 by skillful exercise and use. The training of running and 
 trotting horses has resulted in very greatly increasing 
 the ability of an animal in those particular types of speed. 
 Are these modifications, the result of use or disuse, trans- 
 mitted by heredity? Such inheritance would be of the 
 very greatest importance to the breeder of domestic 
 animals. In answer to this question no direct proof has 
 been offered that characters acquired by exercise or lost 
 by disuse are actually transmitted by heredity. 
 
 201. Importance of causes of variation to the breeder 
 of domestic animals. — While the researches of biologists 
 have led them to believe that the germ-plasm is very 
 stable and its character not easily changed by the environ- 
 ment of the body, it is nevertheless true that breeders of 
 the domestic animals have long believed that the amount 
 and kind of food, climate and training which animals 
 receive has an influence not only upon the individuals 
 benefiting by or suffering from such environment, but 
 likewise may have a profound influence upon their pos- 
 
214 THE BREEDING OF ANIMALS 
 
 terity. The breeder of beef cattle believes that the off- 
 spring of parents which are kept in good or even in fat 
 condition are more apt to possess a tendency to fatten 
 readily than the offspring of parents kept in very thin 
 condition. The breeder of trotting horses prefers to use 
 in his stud a stallion that has a record and mares that 
 have benefited from severe training. 
 
 In this case the biologist ivS, probably in the main cor- 
 rect in his conclusions from the standpoint of inheritance. 
 But it is also true that the breeder of beef cattle is right 
 in maintaining his beef animals on a high plane of nutri- 
 tion, not because this will materially affect the germ-plasm, 
 but because such treatment gives the breeder an accurate 
 measure of the beef-producing characters of his breeding 
 animals. How can the breeder know that a particular 
 bull or cow possesses the ability to lay on fat rapidly 
 unless he actually tests the animal? The breeder of 
 trotting horses likewise cannot judge accurately from an 
 external examination of a horse how fast he can trot. He 
 must be trained and his full speed developed. 
 
 Such treatment on the part of the breeder is not for 
 the purpose of changing the hereditary capacities of an 
 animal, but for the purpose of aiding selection. Animals 
 so treated that do not come up to the standard set by the 
 breeder are eliminated. The desirable animals are pre- 
 served and encouraged to reproduce. 
 
 202. Germinal variations. — The term variation has 
 suffered from careless use, and such use has led to some 
 confusion of ideas. Differences appearing in the offspring 
 may be due to variations in the germ, or they may be due 
 to the influence of environment. What the animal 
 actually is depends upon the constitution of the germ. 
 The offspring may be exactly like the parent in the con- 
 
VARIATION 215 
 
 stitution of the germ substance from which each has 
 been developed, but they may appear to be different. 
 Such differences may be due to a change in the environ- 
 ment which, acting upon the organism, may have modified 
 the apparent character of the individual. Such changes 
 are not variations in the true sense, but rather modifica- 
 tions. It is not always possible to distinguish readily 
 between changes which are merely modifications and 
 variations which are due to fundamental changes in the 
 germ. To the practical breeder, it is in the highest 
 degree important that this distinction between mere 
 modifications due to environment and germinal varia- 
 tions due to a change in the constitution of the germinal 
 substance be clearly recognized. The latter variations 
 are strongly transmitted by heredity; the former are 
 not transmissible. Domestic animals kept under the 
 same conditions often exhibit wide variations, and these 
 are often germinal and consequently inherited. Those 
 variations or, more properly, modifications which appear 
 in individuals and are the result of environment are of 
 little significance to the breeder. If the breeder of speed 
 horses confined his selection solely to those horses that 
 had been trained, he might not secure the sum total of 
 those characters in the fundamental constitution of the 
 animal which represent the highest capacity for speed. 
 It is true that among horses of similar ancestry the train- 
 ing and development is the most accurate index of the 
 capacities which they have inherited. But a horse 
 that has not been trained and hence modified by environ- 
 ment may actually possess through inheritance a greater 
 capacity for speed. The latter horse may show less 
 speed than the horse that has been carefully developed, 
 but he will be a better breeder. Let us assume for example 
 
216 THE BREEDING OF ANIMALS 
 
 that we have two horses under consideration, of the same 
 ancestry. One horse has through germinal variation 
 been endowed with an abihty to trot or run at a certain 
 speed without training. The other horse cannot attain 
 the same speed except as the result of long and careful 
 training. They have attained the same rate of speed, 
 but one has acquired this speed through the influence 
 of environment and this increased speed becomes, there- 
 fore, a mere modification. The other horse owes his 
 ability to go fast to a variation in the fundamental con- 
 stitution of the germ substance. The latter horse will 
 be the better breeder because germinal variations are 
 transmitted, and modifications which result from the 
 influence of environment are apparently not transmitted. 
 
CHAPTER XI 
 IN-BREEDING 
 
 The breeder of domestic animals is frequently confronted 
 with the problem of in-breeding. If in-breeding is not 
 followed by injury, it would often be a convenient method 
 of improvement. The value of a proven and tested sire 
 is so great that if he could be safely mated with his own 
 offspring it would be of great economic advantage to 
 the breeder. If, on the other hand, positive advantages 
 follow the mating of closely related animals, the breeder 
 should know what these advantages are and how and when 
 they may be most certainly realized. 
 
 203. Definitions. — In-breeding has been variously 
 designated as close-breeding, consanguineous breeding, 
 in-and-in-breeding, inter-breeding and incestuous breed- 
 ing. The term in-breeding is used to indicate the mating 
 of animals which are near of kin or closely related. The 
 degree of relationship which it is proper to designate 
 as in-breeding is a matter of some disagreement. Stone- 
 henge, for example, has defined in-breeding as '' The 
 pairing of relations within the degree of second cousins, 
 twice or more in succession." Randall would restrict 
 the application of the term to " animals of precisely the 
 same blood as own brother and sister." 
 
 It would be very desirable if the term " in-breeding " 
 could be limited in its application as suggested by Mor- 
 
 217 
 
218 THE BREEDING OF ANIMALS 
 
 gan} " For species with separate sexes the term ' in- 
 breeding ' is used to express either the union between 
 brothers and sisters or between offspring and parent, in 
 one or more generations." Unfortunately the Hterature 
 on the subject of in-breeding has not placed such narrow 
 limitations on the term. 
 
 It must be recognized that there are different degrees 
 of in-breeding. Animals may be closely in-bred as, for 
 example, results from the mating of parent and offspring, 
 or brother and sister. The union of more distant rela- 
 tionships, as third or fourth cousins, would not be expected 
 to show the same good or bad results in the offspring as 
 the more closely related parents. In the literature of 
 the subject, the discussions generally have reference to 
 the most intensive forms of close-breeding. The results, 
 good or bad, therefore, are those which may be expected 
 to follow the most intensive in-breeding. After all, the 
 real question of importance for the practical breeder to 
 answer is not whether any form of in-breeding should 
 be practiced, but to what extent it may be practiced and 
 its known advantages become realized. In a sense, prac- 
 tically every registered improved breed to-day is the 
 result of a certain amount of in-breeding. David Starr 
 Jordan has calculated that if no in-breeding of any degree 
 had taken place in the human race, each person born 
 in the thirtieth generation from William the Conqueror 
 would have had 8,598,094,592 living ancestors at the 
 time when the Conqueror was alive. 
 
 204. Advantages claimed for in-breeding. — The mat- 
 ing of animals having the same parentage, has resulted 
 in certain definite advantages to the race or breed. These 
 results are as easily demonstrable as are the results from 
 
 1 Morgan, "Experimental Zoology," 1907, p. 186. 
 
IN-BREEDING 219 
 
 any other system or method of breeding. The particular 
 beneficial result most commonly claimed is that in-breed- 
 ing is the quickest method of fixing and perpetuating a 
 desirable character. Closely related animals are most 
 likely to possess the character sought, and mating animals 
 having the qualities which the breeder particularly desires 
 to perpetuate in the breed is the most natural method 
 of accomplishing his purpose. In-breeding tends to in- 
 tensify the good qualities which the breeder is striving 
 to make dominant. It does not cause new and desirable 
 characters to appear, but is merely a method of making 
 the greatest possible use of such characters. 
 
 Thus in-bred animals are strongly prepotent. They 
 possess to an unusual degree the power of fixing their 
 qualities upon their offspring. This is manifestly the 
 most important characteristic in a highly improved breed- 
 ing animal. Next to the possession of the highly improved 
 characters which make the domestic animals useful to 
 man, their ability to transmit those qualities is most 
 important. In-breeding is one certain means of develop- 
 ing the prepotency of animals. 
 
 It is a fundamental principle of breeding that the 
 smaller the number of qualities selected for improvement 
 by the breeder, the more rapid and certain will be his 
 progress in the improvement of the breed. In- 
 breeding tends to reduce the number of characters, sim- 
 plify the breeding operations, and thus makes more 
 certain the continued reappearance of the valuable 
 characters in succeeding generations. 
 
 205. Bad results from in-breeding. — In recounting 
 the well-known benefits which follow intelligent in-breed- 
 ing, it is not intended to convey the impression that 
 in-breeding results only in success. The biological pro- 
 
220 THE BREEDING OF ANIMALS 
 
 cesses which result in simphfying the germ-plasm and 
 intensifying the powers of transmission act impartially 
 on all characters alike, bad as well as good. Lurking 
 tendencies to evil may become strengthened along with 
 the good, and thus be more strongly transmitted than 
 before. 
 
 Such a result cannot always be foreseen and hence 
 when breeding closely related animals, there is always 
 the risk that we will produce offspring which are not only 
 more prepotent in respect to the good qualities we are 
 seeking to develop and perpetuate, but we may at the 
 same time bring about the same result in connection with 
 the bad qualities. 
 
 But aside from the bad results following in-breeding 
 which may be ascribed to the simplifying of the germ- 
 plasm and the intensifying of the tendencies to evil, it 
 has long been held by many eminent biologists and by 
 practical breeders that certain definite evil results always 
 follow long-continued in-breeding. The most important 
 of these necessary evils are loss of vigor, decreased fer- 
 tility and diminished size. 
 
 206. Decreased fertility and vigor from in-breeding. — 
 Many breeders believe that continuous in-breeding results 
 in a loss of fertility. It is admitted that most other 
 qualities may be advantageously improved by close- 
 breeding, but that the quality of fertility is an exception. 
 This belief is firmly implanted in the minds of the greater 
 number of breeders and of many biologists. The basis 
 for such a belief is found in the results of certain specific 
 investigations and the general experience of breeders. 
 Fertility is a character of prime importance in the domestic 
 animals. This character is undoubtedly subject to the 
 same general laws of transmission as are all other hered- 
 
IN-BREEDING 221 
 
 itary qualities. We have seen how in-breeding may be 
 used to intensify and fix the other desirable characters 
 of a breed, and incidentally greatly increase their pre- 
 potency. If an animal is possessed of the quality of 
 fertility to an unusual degree, why may not in-breeding 
 be employed to increase fertility as well as to improve 
 the qualities of speed in horses or of early maturity 
 in meat-producing animals ? Let us answer the question 
 by an examination of the available data. Is in-breeding 
 yer se specifically injurious to the fertility of plants and 
 animals? If in-breeding is injurious at all, how serious 
 is the injury and how far can the breeder take advantage 
 of the known good results without sacrificing the impor- 
 tant quality of fertility ? The data available for answer- 
 ing these questions are to be found in the practical experi- 
 ence of breeders and the results from carefully planned 
 experiments where all other factors have been eliminated 
 excepting only the factor of in-breeding. 
 
 207. Darwin's researches. — The greatest single con- 
 tribution to the subject of in-breeding was made by Dar- 
 win. Recognizing the advantages of close in-breeding 
 in fixing desirable characters and admitting that these 
 advantages may outweigh possible injur^^ he brings 
 forward an array of examples of the injurious effects of 
 in-breeding which are convincing. His conclusions are 
 best stated in his own words : 
 
 ^ " That any evil directly follows from the closest 
 inter-breeding has been denied by many persons ; but 
 rarely by any practical breeder; and never, as far as I 
 know, by one who has largely bred animals which prop- 
 agate their kind quickly. Many physiologists attribute 
 
 ^ Darwin, "Animals and Plants under Domestication," vol. 
 II, p. 94. 
 
222 THE BREEDING OF ANIMALS 
 
 the evil exclusively to the combination and consequent 
 increase of morbid tendencies common to both parents; 
 and that this is an active source of mischief there can be 
 no doubt. It is unfortunately too notorious that men 
 and various domestic animals endowed with a wretched 
 constitution, and with a strong hereditary disposition 
 to disease, if not actually ill, are fully capable of procre- 
 ating their kind. Close inter-breeding, on the other hand, 
 often induces sterility ; and this indicates something quite 
 distinct from the augmentation of morbid tendencies 
 common to both parents. The evidence immediately 
 to be given convinces me that it is a great law of nature, 
 that all organic beings profit from an occasional cross 
 with individuals not closely related to them in blood ; 
 and that, on the other hand, long-continued close inter- 
 breeding is injurious." 
 
 Darwin's conclusions are based upon a very large 
 number of observations. Experienced breeders who are 
 accurate observers, such as Sir J. Sebright,^ Andrew 
 Knight and Herman von Nathusius, all agree as to the 
 certain injury which always follows long-continued in- 
 breeding. 
 
 Darwin's investigations led him to believe that while 
 many species of plants and animals are hermaphroditic 
 and hence self-fertilizing, and these might be presumed 
 perpetually to fertilize themselves, yet he failed to find 
 a single species in which nature had provided structures 
 which insured self-fertilization. On the other hand, he 
 found innumerable instances in which nature had pro- 
 vided special structures for the sole apparent purpose of 
 insuring cross-fertilization and thus preventing perpetual 
 in-breeding. 
 
 1 Sebright, "The Art of Improving the Breed," 1809. 
 
IN-BREEDING 223 
 
 208. In-breeding cattle. — BakewelFs ^ (1725-1795) 
 phenomenal success in the rapid improvement of horses, 
 cattle and sheep was possible only because he utilized 
 to the fullest extent the method of mating animals of 
 the closest possible relationship, not because they were 
 closely related but because they possessed the particular 
 qualities desired. By in-breeding he was able to " sim- 
 plify " the germ-plasm and bring about a homozygous 
 condition of these particular characters. The available 
 breeding records of the activities of Robert and Charles 
 Colling, Thomas Bates and the Booths are eloquent in 
 their testimony of the fact that great progress was achieved 
 from intelligent in-breeding. 
 
 The Shorthorn bull, Duke of Airdrie (12,730),2 traces 
 through five or six generations to but six animals famous 
 in the early history of the Shorthorn breed. The six 
 animals all trace back through five or six generations to 
 one bull Favourite, himself the son of half-brother and 
 sister. Says Darwin,^ " But the Shorthorns offer the 
 most striking case of close inter-breeding ; for instance, 
 the famous bull Favourite (who was himself the offspring 
 of a half-brother and sister from Foljambe) was matched 
 with his own daughter, granddaughter, and great-grand- 
 daughter; so that the produce of this last union, or the 
 great-great-granddaughter, had 15-16ths, or 93.75 per 
 cent of the blood of Favourite in her veins. This cow 
 was matched with the bull Wellington, having 62.5 per 
 cent of Favourite blood in his veins, and produced Cla- 
 rissa ; Clarissa was matched with the bull Lancaster, hav- 
 
 lYouatt, ''Cattle," p. 199. 
 
 2 A valuable discussion of in-breeding among early breeders 
 is to be found in Miles' "Stock Breeding," pp. 137-189. Also 
 Huth, "The Marriage of Near Kin," pp. 242-292. 
 
 ^ Darwin, "Animals and Plants under Domestication," p. 96. 
 
224 THE BREEDING OF ANIMALS 
 
 ing 68.75 of the same blood, and she yielded valuable 
 offspring. Nevertheless Collings, who reared these ani- 
 mals, and was a strong advocate for close-breeding, once 
 crossed his stock with a Galloway, and the cows from 
 this cross realized the highest prices. Bates's herd was 
 esteemed the most celebrated in the world. For thirteen 
 years he bred most closely in-and-in ; but during the 
 next seventeen years, though he had the most exalted 
 notion of the value of his own stock, he thrice infused 
 fresh blood into his herd : it is said that he did this, not 
 to improve the form of his animals, but on account of 
 their lessened fertility." 
 
 The opinion of a great breeder who has practiced 
 very close in-breeding for eighty years and who has also 
 been noted for the general success of his breeding opera- 
 tions and the high quality of his cattle, so much so as to 
 have been called one of the founders of the breed, is of 
 great interest in this connection. Such a breeder was 
 Price of England. He says,^ " My herd of cattle has, 
 therefore, been bred in-and-in, as it is termed, for upward 
 of eighty years, and by far the greater part of it in a direct 
 line, on both sides, from one cow now in calf for the twen- 
 tieth time. I have bred three calves from her, by two 
 of her sons, one of which is now the largest cow I have, 
 possessing also the best form and constitution ; the other 
 two were bulls, and proved of great value, thus showing 
 indisputably that it is not requisite to mix the blood of 
 the different kinds of the same race of animals, in order 
 to keep them from degenerating." 
 
 209. The Chillingham cattle. — The wild white cattle 
 of Great Britain are believed to be the only living pure 
 descendants of the original wild cattle of the British Is- 
 
 1 Farmers' Magazine, 1841, vol. XIV, p. 50. 
 
IN-BREEDING 225 
 
 lands. These cattle have been kept pure in various 
 private parks of Great Britain and have for many hundred 
 years been subjected to conditions which compelled 
 extensive in-breeding. These cattle have not perished, 
 they are not weak in constitution and are not decreasing 
 in size. This example is often quoted as an argument 
 in favor of in-breeding. Darwin's critical analysis of 
 this classic example leaves us still in doubt as to its value 
 as a demonstration of the beneficial results which may be 
 expected to follow long-continued in-breeding. 
 
 ^ " The half-wild cattle," says Darwin, " which have 
 been kept in British parks probably for 400 or 500 years, 
 or even for a longer period, have been advanced by Culley 
 and others as a case of long-continued inter-breeding within 
 the limits of the same herd without any consequent injury. 
 With respect to the cattle at Chillingham, the late Lord 
 Tankerville owned that they were bad breeders. The 
 agent, Mr. Hardy, estimates (in a letter to me dated 
 May, 1861) that in the herd of about 50 the average num- 
 ber annually slaughtered, killed by fighting and dying, 
 is about 10, or one in five. As the herd is kept up to 
 nearly the same average number, the annual rate of in- 
 crease must be likewise about one in five. The bulls, 
 I may add, engage in furious battles, of which battles 
 the present Lord Tankerville has given me a graphic 
 description, so that there will always be rigorous selec- 
 tion of the most vigorous males. I procured in 1855 
 from Mr. D. Gardner, agent to the Duke of Hamilton, 
 the following account of the wild cattle kept in the Duke's 
 park in Lanarkshire, which is about 200 acres in extent. 
 The number of cattle varies from 65 to 80 ; and the num- 
 ber annually killed (I presume by all causes) is from 8 
 
 1 Darwin, "Animals and Plants under Domestication," p. 97. 
 Q 
 
226 THE BREEDING OF ANIMALS 
 
 to 10; so that the annual rate of increase can hardly be 
 more than one in six. Now in South America, where 
 the herds are half-wild, and therefore offer a nearly fair 
 standard of comparison, according to Azara the natural 
 increase of cattle on an estancia is from one-third to one- 
 fourth of the total number, or one in between three and 
 four, and this no doubt applies exclusively to adult ani- 
 mals fit for consumption. Hence the half-wild British 
 cattle which have long been inter-bred within the limits 
 of the same herd are relatively far less fertile. Although 
 in an unenclosed country like Paraguay there must be 
 some crossing between the different herds, yet even there 
 the inhabitants believe that the occasional introduction 
 of animals from distant localities is necessary to prevent 
 ' degeneration in size and diminution in fertility.' The 
 decrease in size from ancient times in the Chillingham 
 and Hamilton cattle must have been prodigious, for 
 Professor Rutimeyer has shown that they are almost 
 certainly descended from the gigantic bos primigenius. 
 No doubt this decrease in size may be largely attributed 
 to less favorable conditions of life ; yet animals roaming 
 over large parks, and fed during severe winters, can hardly 
 be considered as placed under very unfavorable condi- 
 tions." 
 
 210. Deer in parks. — In many English parks fallow 
 deer have been kept for many decades, and in-breeding 
 must often result. An investigation by Darwin dis- 
 closed the fact that the managers of such parks found it 
 necessary to introduce new blood to improve the size, 
 constitution, vigor and prevent the taint of " rick back," 
 which follows too close breeding. 
 
 211. In-breeding among pigs. — The evil results from 
 in-breeding are naturally more quickly apparent among 
 
IN-BREEDING 227 
 
 animals which produce large numbers of young at a birth 
 and have a comparatively short period of gestation. 
 Domestic swine fulfill these conditions admirably and 
 are therefore most valuable material for breeding experi- 
 ments. 
 
 ^ '' Mr. J. Wright, well known as a breeder, crossed 
 the same boar with the daughter, granddaughter, and 
 great-granddaughter, and so on for seven generations. 
 The result was, that in many instances the offspring failed 
 to breed; in others they produced few that lived; and 
 of the latter many were idiotic, without sense, even to 
 suck, and when attempting to move could not walk 
 straight. Now it deserves especial notice, that the two 
 last sows produced by this long course of inter-breeding 
 were sent to other boars, and they bore several litters 
 of healthy pigs. The best sow in external appearance 
 produced during the whole seven generations was one 
 in the last stage of descent; but the litter consisted of 
 this one sow. She would not breed to her sire, yet bred 
 at the first trial to a stranger in blood. So that, in Mr. 
 Wright's case, long-continued and extremely close inter- 
 breeding did not affect the external form or merit of the 
 young; but with many of them the general constitution 
 and mental powers, and especially the reproductive func- 
 tions, were seriously affected." 
 
 Nathusius reports that as a result of closely in-breed- 
 ing Yorkshire swine for three generations the offspring 
 were weak in constitution and their fertility was impaired. 
 
 212. In-breeding sheep. — The American Merino sheep 
 is a remarkable example of what intelligent breeding and 
 
 1 Darwin, "Animals and Plants under Domestication," p. 
 101. 
 
 Also Journal of Royal Agricultural Society, 1846, vol. 7, p. 205. 
 
228 THE BREEDING OF ANIMALS 
 
 selection can accomplish in the improvement of the 
 domestic animals. The first importation of Spanish 
 Merino sheep to America was made in 1815. The aver- 
 age weight of fleece of these sheep at that time was 
 three or four pounds a head. This average was in- 
 creased by- American breeders until, in 1880, the average 
 fleece from selected flocks was fifteen pounds a head, and 
 single individuals were produced which sheared as high 
 as thirty-five pounds. Plumb ^ reports that the heaviest 
 fleece on record weighed 44 pounds and 3 ounces and was 
 taken from a two-year-old ram at the public shearing 
 of the Vermont Sheep Shearing Association. But the 
 finest specimens of the American Merino breed were the 
 result of in-breeding. '' Mr. Atwood bred his entire flock 
 from one ewe, — and thus, after being drawn beyond all 
 doubt from an unmixed Spanish Cabana, they have 
 been bred in-and-in, in the United States, for upward 
 of sixty years." ^ " The ram Gold Drop for which Mr. 
 Hammond refused twenty-five thousand dollars," ^ was 
 closely in-bred. 
 
 213. In-breeding dogs. — Many examples of in-breed- 
 ing among dogs are mentioned in the literature of breed- 
 ing, but unfortunately the records of these cases are very 
 incomplete and many are of doubtful scientific value. 
 The author has had an opportunity to examine somewhat 
 carefully the results of long-continued in-breeding among 
 fox terriers. Arthur Rhys, the herdsman at the University 
 of Missouri, has practiced very close in-breeding of fox 
 terriers for nine generations. Daughter No. 1, from 
 wholly unrelated parents, was bred back to Designer, her 
 
 ^ Plumb, "Types and Breeds of Farm Animals," p. 349. 
 
 2 Randall, "Practical Shepherd." 
 
 3 Miles, "Stock Breeding," p. 150. 
 

 f » .*-^» 
 
 Plate XIV. — Upper. Close in-breeding of fox terrier. "Dis- 
 patcher" at age nine months ; ninth generation of intense in-breeding. 
 Lower. "Designer 2d" at age four months; eighth generation of in- 
 tense in-breeding. 
 
IN-BREEDING • 229 
 
 own sire, producing two litters of six and seven each. 
 Female No. 2, a daughter of No. 1, was bred to Designer, 
 her own sire, who was also her grandsire. She produced 
 a litter of eight. Female No. 3, a daughter of No. 2, 
 was bred again to Designer, her own sire, who was also 
 her grandsire and great-grandsire. Female No. 4 was 
 again bred to Designer, her own sire, who was also 
 her grandsire, great-grandsire and great-great-grandsire. 
 She produced a litter of eight. Thus in turn Females 
 Nos. 5, 6, 7 and 8 were bred to their own sire, Designer. 
 Female No. 8, resulting from this long-continued in-breed- 
 ing, was bred to her own son, and from the litter result- 
 ing a brother and sister were selected and in-bred. Mr. 
 Rhys states that, " I see no evidence of decrease in size 
 of bone, in constitution or in fertility as a result of my 
 experience in in-breeding fox terriers." The only pecul- 
 iarity which has been observed in the later generations 
 as compared with the original animals is a slight lack of 
 courage or " nerve " in the later animals. A normal fox 
 terrier never flinches in the face of sudden danger. 
 
 The illustration, Plate XIV, lower, represents Designer 
 II, at four months old, one of the seven dogs in the 
 eighth generation of continuous in-breeding. Every litter 
 for eight generations was sired by Designer I. The illus- 
 tration, Plate XIV, upper, pictures the dog Dispatcher of 
 the ninth generation, son of own brother and sister. 
 
 214. Cornevin's ^ experiments. — The French breeder 
 and author, Cornevin, practiced in-breeding with swine, 
 cattle and sheep for considerable periods without injury. 
 He in-bred Jersey cattle for seven years, Hollander cattle 
 for twelve years, and Merino sheep eleven years without 
 observing any evidences of degeneracy. His experi- 
 
 1 Cornevin, "Traite de Zootechnie Generale " (1891). 
 
230 THE BREEDING OF ANIMALS 
 
 ments with swine were unfavorable to the practice of 
 in-breeding. According to Cornevin, among pigeons it 
 is the rule for brother and sister to mate. The same 
 is also generally true of ducks, geese, guinea fowls 
 and swans. After eleven years of in-breeding pigeons 
 and geese, he was unable to observe any changes in 
 color, weight or fecundity which could be ascribed to 
 in-breeding. 
 
 Georg Wilsdorf,^ the German authority, has found 
 by investigation that most pure breeds have resulted 
 from in-breeding. He says, " In our studies of the his- 
 tory of various breeds, we next made the astonishing 
 discovery that the best living individuals belonged to 
 families which, when their pedigrees were traced, were 
 found all to come from a single family — often from a 
 single individual. By way of illustration I might cite 
 the Hanoverian halfbloods, which we know particularly 
 through the studies of de Chapeaurouge and Grabensee 
 to have come almost altogether from three stallions, of 
 which Norfolk has hitherto had the greatest influence on 
 the breed — an influence that is increasing all the time. 
 Researches into the swine breeding of the Visselhovede 
 district, and into that of Hildesheim in Bavaria, have 
 shown that in each case a single boar was the ancestor 
 of various valuable families, to-day widely scattered. 
 And Hoesch of Neukirchen has found that his valuable 
 strain of swine is principally due to the blood of a single 
 early boar Richard." 
 
 " The modern science of breeding, however, stands 
 firm in its belief that for the production of definite types 
 for special purposes in-breeding is the quickest and most 
 certain method of procedure, and all great breeders who 
 
 1 Journal of Heredity, March, 1915, pp. 110-111. 
 
IN-BREEDING 231 
 
 work toward any particular goal depend largely on in- 
 breeding, knowingly or unknowingly." ^ 
 
 215. Weismann's and Von Guaita's experiments. — 
 Weismann ^ in-bred mice for twenty-nine generations. As 
 shown in the following table, there was a constant and 
 fairly uniform decrease in fertility from the first to the 
 last generation : 
 
 1 to 10 generations ; 1345 young ; 219 litters ; avg. per litter 
 
 6.1 
 
 11 to 20 generations; 252 young; 62 litters; avg. per litter 
 
 5.6 
 
 21 to 29 generations ; 124 young ; 29 litters ; avg. per litter 
 
 4.2 
 
 The average number of young to a litter decreased from 
 6.1 in the first ten generations to 4.2 in the last ten genera- 
 tions. Whether this decrease is due directly to the specific 
 action of in-breeding on the quality of fertility, or whether 
 it simply represents an intensification of an innate tend- 
 ency to low fertility which existed in this particular strain, 
 it is not possible to determine. Von Guaita, working 
 with the same strain of mice and beginning with the 
 last generation (29th) bred by Weismann, obtained the 
 following results : 
 
 1st and 2d generations, avg. per litter, 3.5 
 3d and 4th generations, avg. per litter, 3.6 
 5th and 6th generations, avg. per litter, 2.9 
 
 There is here a clear loss of fertility from an average 
 of 6.1 to a litter to 2.9 to a litter in 35 generations, trace- 
 able to in-breeding. 
 
 1 Georg Wilsdorf, "Tierzuehtung," 1912. 
 
 2 "Berichte der Naturforschenden Gesellschaft zu Freiburg," 
 1900. 
 
 See Morgan, "Experimental Zoology," p. 188. 
 
232 THE BREEDING OF ANIMALS 
 
 216. Researches of Ritzema Bos. — An interesting 
 experiment with in-breeding white rats for thirty genera- 
 tions is reported by Ritzema Bos.^ Beginning with an 
 albino female mated with a wild rat, the first mating re- 
 sulted in twelve offspring. Seven of this litter were 
 bred to a white male but unrelated. The resulting off- 
 spring were closely in-bred for six years. The matings 
 were brothers to sisters and parents to offspring. The 
 average size of the litters for twenty generations and 
 covering a period of four years remained practically 
 constant. The last ten generations born during the 
 last two years of the experiment showed a decided decrease 
 in the fertility of the matings. The average size of 
 litters by years is shown in the table. 
 
 Decreased Fertility Due to In-breeding. (Bos) 
 
 1887 
 
 1888 
 
 1889 
 
 1890 
 
 1891 
 
 1892 
 
 7i 
 
 71 
 
 '712 
 
 7t7 
 
 6fi 
 
 4tV 
 
 3i 
 
 Not only the average size of the litters decreased in 
 thirty generations from 7J to 3j, but the number of mat- 
 ings which were sterile increased greatly from the first 
 to the last generations, as shown in the following table : 
 
 Matings Which Proved Sterile. (Bos) 
 
 1887 
 
 1888 
 
 1889 
 
 1890 
 
 1891 
 
 1892 
 
 
 
 2.63 
 
 5.55 
 
 17.39 
 
 50 
 
 41.18 
 
 There is evidence also in this experiment that the 
 constitutional vigor of the offspring of parents which 
 were the result of long-continued in-breeding was materi- 
 ally injured. The time of the appearance of weakness 
 
 1 Ritzema Bos, "Biol. Centralb.," XIV, 1894. See alsoMor- 
 gan, "Experimental Zoology," p. 188. 
 
IN-BREEDING 233 
 
 in the offspring was coextensive with the decHne in 
 fertihty. 
 
 The comparative mortaHty of the young increased 
 rapidly, as shown in the following table : 
 
 Increased Rate of Mortality Due to In-breeding. (Bos) 
 
 1887 
 
 1888 
 
 1889 
 
 1890 
 
 1891 
 
 1892 
 
 Per cent 
 
 Per cent 
 
 Per cent 
 
 Per cent 
 
 Per cent 
 
 Per cent 
 
 3.9 
 
 4.4 
 
 5.0 
 
 36.7 
 
 36.4 
 
 45.5 
 
 The bad effects from in-breeding were more noticeable 
 when brother and sister were mated than when parents 
 were mated with offspring. Of the matings between 
 parent and offspring 21.4 per cent were sterile, while 
 those between brother and sister were 36 per cent infertile. 
 A tendency to decrease in size is indicated by the record 
 of weights of different generations. Full-grown male 
 rats of the first generation weighed 300 grams each. In 
 the tenth generation the weight had decreased to 275 
 grams and at the end of six years the weight of rats had 
 declined to 240 grams. 
 
 217. The Wistar Institute experiments. — Extensive 
 in-breeding experiments by Helen Dean King ^ at the 
 Wistar Institute, Philadelphia, with white rats seem to 
 have resulted in disproving the theory that in-breeding 
 is always and necessarily followed by evil results. In 
 this investigation white rats have been as closely in-bred 
 as possible for twenty-two generations. More than 
 10,000 in-bred rats have been observed during a period 
 of seven years. The original stock was two pairs of 
 albino rats. Each pair was used as the foundation for a 
 series of in-breeding experiments. In each generation 
 
 1 Journal of Heredity, vol. 7 (1916), p. 70. 
 
234 THE BREEDING OF ANIMALS 
 
 the best rats from the standpoint of size, vigor, fecundity 
 and general quaHty were carefully selected. 
 
 The actual results of this investigation after twenty- 
 two generations of in-breeding are that the male in-bred 
 rats are about fifteen per cent heavier and the female 
 in-bred rats about three per cent heavier than stock rats. 
 The size of litters among the stock rats has been seven, 
 while among the in-bred rats the litters have increased 
 and now average seven and four-tenths each. The thrift 
 and vigor of in-bred rats in these experiments was appar- 
 ently not injured by in-breeding. " The results so far 
 obtained with these rats," says Dr. King, " indicate 
 that close in-breeding does not necessarily lead to a loss 
 of size or of constitutional vigor or of fertility, if the 
 animals so mated come from sound stock in the beginning 
 and sufficient care is taken to breed only from the best 
 individuals." 
 
 218. In-breeding Berkshires by Mr. Gentry. — The 
 remarkable success which may follow the practice of 
 in-breeding when intelligently conducted by a skillful 
 breeder is shown in the experience of N. H. Gentry of 
 Sedalia, Missouri. Probably no American breeder has 
 been so successful in developing all those desirable qualities 
 in Berkshire swine which give this breed its great economic 
 value. At the Chicago World's Fair in 1893 Gentry's 
 Berkshires won twenty-three of the twenty-eight first 
 prizes offered, and many of the other winners were de- 
 scended from stock bred by him. At the St. Louis World's 
 Fair in 1903, all the Berkshires which came within the 
 five cash prizes offered, with three exceptions, were de- 
 scended from animals bred by Gentry. The entire 
 Gentry herd was strongly in-bred, carrying a very high 
 proportion of the blood of Longfellow. Describing his 
 
IN-BREEDING 235 
 
 breeding practice, Gentry says:^ *'It has long been con- 
 ceded that Longfellow 16,835 was the greatest boar known 
 to the breed, in this country at least. He was out of an 
 imported sow and one of the best I ever saw. His sire, 
 Charmar's Duke 13,360, I bred, and he was a great one, 
 too. He was sired by an imported boar and was out of 
 an imported sow, and this sow and the dam of Longfellow 
 were got by the same boar. After the death of Charmar's 
 Duke 13,360, which happened when he was only a two- 
 year-old, I kept his best son, Longfellow, and after I^ong- 
 fellow's death his best sons, and after their death, their 
 best sons. Thus Longfellow, Longfellow's sons, and now 
 his grandsons, have followed each other in use on my herd. 
 One of the largest and best boars I have ever produced, 
 one which I showed at the World's Fair at Chicago in 
 1893, weighing at 13 months and 6 days of age, 660 pounds, 
 with as much action, strength, vigor and masculine 
 development as any boar I ever saw, was produced by a 
 son of Longfellow out of a daughter of Longfellow sired 
 by the sire of Longfellow. Thus the three top successive 
 sires in his pedigree were the sire of Longfellow, Longfellow 
 and a son of Longfellow. I could name many good ones 
 bred as closely and, in fact, almost every animal in my 
 herd has been produced by as close in-breeding on both 
 sides." (See Plate XV.) 
 
 " I have practiced in-breeding more from necessity 
 than from any other reason. I believe I have not used a 
 boar other than my own breeding for twenty years." 
 
 After a lifetime's experience with in-breeding the 
 conclusions of Gentry are significant : " If it is true that 
 in-breeding intensifies weakness of constitution, lack of 
 vigor, or too great fineness of bone, as we all believe, is 
 
 1 Gentry, Amer. Breeders' Assoc, vol. I, 1905, pp. 170-171. 
 
236 THE BREEDING OF ANIMALS 
 
 it not as reasonable and as certain that you can intensify 
 strength of constitution, heavy bone, or vigor, if you have 
 those traits well developed in the blood of the animals 
 you are in-breeding ? I think I have continued to improve 
 my herd, being now able to produce a larger percentage 
 of really superior animals than at any time in the past ..." 
 
 Another noted breeder of Berkshires who attributes 
 the high quality of his animals to the practice of in-breed- 
 ing is A. J. Lovejoy of Illinois. He is quoted in Daven- 
 port's " Principles of Breeding " as follows : 
 
 ^ " We are believers in quite close, even in-breeding. 
 We find the greatest show animals are closely in-bred. 
 Sires to half-sisters is the most common form of close 
 breeding, though cousins, nephews, and nieces, and even 
 brothers and sisters are bred together with great success. 
 It of course requires good judgment in mating animals 
 that are particularly strong in individual merit. Should 
 each have a bad defect in any way, we should expect 
 that to be more manifest in the offspring than in the par- 
 ents, and likewise the good points would be better; so 
 if one mates equally good specimens the produce will be 
 an improvement. There is no sire of any breed so pre- 
 potent as an in-bred sire. When we get to the point 
 where we feel the need of outside blood we mate an im- 
 ported sow with our best boar, and from this litter we 
 select a boar to use on the get of his own sire from other 
 sows in the herd ; that is, we breed this boar on his own 
 half-sisters." 
 
 219. In-breeding com. — Many of the principles which 
 are now universally accepted as guides to practice in 
 animal-breeding were first discovered by plant-breeders. 
 The mendelian principle is a good example of this fact. 
 
 1 Davenport, "Principles of Breeding," p. 625. 
 
IN-BREEDING 237 
 
 While the fundamental principles governing the trans- 
 mission of characters are the same in plants and animals, 
 the practical applications are sometimes widely different. 
 Wholesale advice based wholly upon plant investigations, 
 therefore, and intended to guide the practical breeder 
 of animals is not always justified for obvious reasons. 
 The experiments conducted for the purpose of testing 
 the effects of in-breeding on Indian corn {Zea Mays) have 
 been extensive. In every case, so far as the author has 
 been able to determine, in-breeding corn has resulted in 
 decreased yields if long continued. Hayes ^ and East 
 found that " the first generation of in-breeding has the 
 greatest detrimental effect." The injury from in-breed- 
 ing is not continuous, but results in separating the pure 
 lines in a variety. When once a pure line is produced 
 by in-breeding, further in-breeding apparently does not 
 reduce the yield. Shamel ^ found that four generations 
 of self-fertilization of corn so weakened the strain that 
 the seed failed to germinate. Darwin, experimenting 
 with morning glories (Ipomsea) for a period of ten years, 
 found that the strain which was screened so that insects 
 could not bring about cross-fertilization lost in vigor 
 as compared with a similar strain which had beeen left 
 in the open and cross-fertilized through the agency of 
 insects. 
 
 Wheat is a self-fertilizing plant. Unnumbered genera- 
 tions of in-breeding seem not to have decreased its vigor 
 or lowered its fertility. Castle in-bred brother and sister 
 of Drosophila (pomace fly) for 59 generations. No loss 
 of fertility or vigor was observed. 
 
 1 Hayes and East, Bui. 168, Connecticut Agricultural Experi- 
 ment Station, p. 11. 
 
 2 Shamel, U. S. Dept. of Agr., Year Book, 1905, p. 388. 
 
238 THE BREEDING OF ANIMALS 
 
 Among the domestic animals it is quite probable that 
 the effects of in-breeding on different species will differ 
 materially. 
 
 220. How long is it safe to continue in-breeding. — 
 If we limit the application of the term in-breeding to mat- 
 ings between parent and offspring or between brother 
 and sister, then we cannot escape the conclusion that 
 long-continued in-breeding results in decreasing fertility, 
 and probably also weakens the constitution and decreases 
 the size of the offspring. ^ " Continued in-breeding," 
 says Kraemer, '' always must result in weakened con- 
 stitution through its own influence." But such results 
 follow long-continued in-breeding. What are the limits 
 of safety? How long may the domestic animals be 
 closely in-bred without injury? An answer to these 
 questions is only possible when all the conditions are 
 known, including a knowledge of the inherited tendencies 
 of the in-bred animals. But it seems entirely safe to 
 conclude from the evidence available that the almost 
 universal prejudice against the practice of in-breeding 
 is in a large degree unwarranted. Such a prejudice 
 has undoubtedly limited the usefulness of many valuable 
 breeding animals and has caused real economic loss to 
 many breeders. 
 
 221. Selection important. — The practice of in-breed- 
 ing will never be successful in the absence of rigorous 
 selection. As the undesirable qualities are transmitted 
 with the same intensity as the good, constant vigilance 
 is required to guard against bringing forward latent char- 
 acters which are less desirable. Particularly animals 
 
 ^ Kraemer, "Mitteilung der Deutsches Landwirtschafts 
 Gesellschaft," September, 1913. See also Journal of Heredity, 
 1914, p. 226. 
 
IN-BREEDING 239 
 
 which are undersize, weak in constitution, or that show a 
 tendency to low fertihty should not be in-bred. It is 
 not always possible to detect the presence of these tend- 
 encies in a single generation, hence a knowledge of family 
 history and pedigree is important. Given an animal 
 of unusual merit with strong constitution, good size and 
 strongly fertile, the breeder runs little risk in practicing 
 in-breeding for a limited time. 
 
 222. The truth about in-breeding. — In the midst of 
 such diversity of opinion as exists concerning the results 
 and value of in-breeding, the practical breeder may well 
 be puzzled. Sweeping generalizations either for or against 
 the practice are apparently unwise at this time. An 
 unreasoning prejudice against the practice will result in 
 withholding from breeders a valuable method of breed- 
 ing which has been in many cases the chief reliance of 
 the world's greatest improvers of the domestic animals. 
 On the other hand, a blind following of those enthusiasts 
 who have claimed for in-breeding some mysterious power 
 in the improvement of animal character will certainly 
 lead to disaster. 
 
 The practice of in-breeding has been compared to a 
 powerful medicine which in the hands of a skillful physi- 
 cian may decide the issues of life, but in the hands of the 
 novice becomes a dangerous and often fatal instrument. 
 In-breeding may be practiced successfully, but only by 
 those who are familiar with the biological principles 
 involved, and who are familiar with the results which 
 sometimes follow the mating of nearly related animals and, 
 what is quite as important, who know the ancestral his- 
 tory of their breeding stock. 
 
 Whether we accept the view that evil is an incidental 
 result due to the intensification of undesirable qualities 
 
240 THE BREEDING OF ANIMALS 
 
 already existing in the germ-plasm of the parent stock, or 
 whether we hold that certain definite evils are a necessary 
 result of mating animals of near kin, we must admit that 
 in-breeding has often been practiced with great success 
 and no appreciable injury. It is, therefore, clearly appar- 
 ent that there are conditions which are neither unusual 
 nor extremely rare under which in-breeding can be prac- 
 ticed with the assurance of success. 
 
 223. Fixing characters by in-breeding. — In-breeding 
 has been a powerful means of fixing and perpetuating 
 valuable characteristics in the domestic animals. It is 
 still a valuable method to be employed for the same pur- 
 pose. But in-breeding is only a means to an end and not 
 the end. In-breeding possesses no magic or occult power 
 which will be exerted for the improvement of animals. 
 While it works powerfully in fixing the good qualities, 
 it is no less potent in firmly establishing undesirable 
 qualities which may be present in the parent stock. And 
 in this fact lies the chief danger from in-breeding. In 
 fixing the good characters, we may unconsciously 
 strengthen the powers of transmission in the direction 
 of bad qualities. The most skillful breeders are less 
 likely to err in the direction of perpetuating tendencies 
 to evil, and history gives ample confirmation of the cer- 
 tain good which does follow in-breeding when practiced 
 with intelligence by skillful and experienced breeders 
 and accompanied by rigorous selection. 
 
 It has often happened in the experience of breeders that 
 a sudden mutation has appeared in a single animal. This 
 mutation may represent a high degree of improvement in a 
 certain character or characters which the breeder has 
 long sought to develop in his breeding stock. This 
 variation appears in one animal only. It is highly 
 
IN-BREEDING 241 
 
 desirable not only to perpetuate this improved character 
 but to breed animals that have this quality in as pure 
 and dominant a state as in the original animal. This 
 can be accomplished by in-breeding. No other method 
 is available which will so quickly and certainly result in 
 producing offspring of similar or identical blood lines. 
 The history of animal-breeding is rich in instances of 
 great animals, famous for their individual excellence 
 but more famous because they have left a heritage 
 of potent '' blood " which has established a new and 
 better strain or even a new breed. We need only 
 recall the names of Favourite, the Shorthorn bull, Justin 
 Morgan, the founder of the Morgan breed, Hambletonian 
 10, the forerunner of the American trotting horse, and 
 scores of individuals of lesser note belonging to practically 
 every modern breed. In many of the instances to which 
 reference is here made, the great individuals would never 
 have become famous if breeders had not recognized their 
 peculiar excellences and have insured the perpetuation 
 of their valuable characters by in-breeding. 
 
 224. In-breeding and prepotency. — The prepotency 
 of animals is increased by in-breeding. There is unanimity 
 among investigators and practical breeders on this point. 
 By continuous in-breeding we may " breed out " less 
 desirable qualities, that is, in the light of mendelism the 
 characters in the germ-plasm tend to become homozygous. 
 In-bred animals are " pure-bred " animals not only in the 
 parlance of the breeder but also from the standpoint of 
 genetics. Mating animals of diverse characters tends 
 to destroy prepotency. Mixing the blood of animals of 
 widely differing characteristics results in making the 
 constituent characters of the germ-plasm heterozygous. 
 The cross-bred animal is never prepotent. 
 
 R 
 
242 THE BREEDING OF ANIMALS 
 
 225. Results of in-breeding vary with different species. 
 
 — The varying opinions regarding the benefits or injuries 
 from in-breeding may in part be accounted for from the 
 fact that investigators have based their conclusions upon 
 data gathered from researches on widely differing species 
 of animals and plants. The effects of in-breeding are quite 
 different in different species or families. Among plants, 
 nature seems to have designed some species especially to 
 insure cross-fertilization and to guard against self-fertili- 
 zation, while other species are self-fertilizing. Indian 
 corn (Zea Mays) is a good example of the former class 
 of plants. The results of continuous in-breeding on the 
 maize plant are markedly injurious. Shull found that 
 continual self-fertilization in Indian corn resulted in a 
 loss of vigor. There are other plants like wheat that are 
 self -fertilizing, and it is difficult to see how in-breeding 
 can be injurious in such species. 
 
CHAPTER XII 
 CROSS-BREEDING 
 
 The term crossing or cross-breeding, like the term 
 in -breeding, is not capable at this time of exact definition. 
 In general we may define cross-breeding as the mating of 
 individuals which are not related. The literature of the 
 subject indicates that this term has been loosely applied. 
 Some indeed have used the term to designate the mating 
 of individuals belonging to different families within the 
 same breed. As a rule, cross-breeding means the mating 
 of individuals belonging to different breeds, as a cross 
 between the Shorthorn and Hereford ; or the union of 
 animals belonging to different species, as a cross between 
 the stallion and the jennet. Cross-breeding has been 
 strongly recommended by some breeders as a valuable 
 method of improving the domestic animals. 
 
 226. Permanent and temporary results of cross-breed- 
 ing. — In recommending cross-breeding, the advocates of 
 this practice have not always been careful clearly to 
 differentiate between the permanent and lasting results 
 of cross-breeding and the more immediate and tem- 
 porary advantages. The effect of cross-breeding upon 
 the purity of the heritable characters of the breed as 
 represented by the germinal elements in the germ-plasm 
 is one thing, while the more or less temporary effect on the 
 body-cells may be quite another thing. The purpose of 
 the breeder of pure-bred registered animals is to establish 
 
 243 
 
244 THE BREEDING OF ANIMALS 
 
 a race of animals that will breed true. It matters not how 
 many good qualities the individual breeding animal may 
 possess ; if he cannot transmit these good qualities to 
 his offspring, he is not a desirable animal for breeding 
 purposes. He may be valuable for commercial purposes. 
 Such an animal might be a fast horse, a prize-winning 
 beef animal, or a great producing cow, but lacking the 
 ability to transmit these qualities this animal would not 
 be a desirable or valuable individual in a breeding herd. 
 It may be quite possible, therefore, for a method of breed- 
 ing to have a distinct economic value for the production 
 of commercial animals and at the same time be a very 
 bad method for the breeder of improved live-stock whose 
 purpose is to produce animals for breeding purposes and 
 not for slaughter or work. What effect does cross-breed- 
 ing have on the breeding powers of the domestic animals ? 
 What value, if any, has cross-breeding in the production 
 of animals for commercial purposes and which are not 
 intended to be used for breeding ? The breeder's interest 
 in cross-breeding will naturally center about the relations 
 of this practice to heredity. 
 
 227. Advantages from cross-breeding. — Breeders of 
 the domestic animals have frequently practiced cross- 
 breeding in the belief that certain very definite and specific 
 benefits followed such practice. In attempting to analyze 
 the reasons for practicing cross-breeding, it is apparent 
 that this has been generally followed for one or more of 
 the following reasons, — to increase fertility, to restore 
 weakened constitution, to increase the size or for improve- 
 ment. 
 
 228. Grading. — The practice of grading, by which 
 is meant the improvement of native or unimproved ani- 
 mals by mating with pure-bred or registered animals, 
 
CROSS-BREEDING 245 
 
 should not be confused with cross-breeding. Cross- 
 breeding is the union of two or more distinct races or 
 breeds, while grading is an attempt gradually to develop 
 a type by continually breeding to pure-bred sires. 
 
 Grading is one of the most successful and certain 
 methods of improvement. There are many examples 
 of successful grading among the breeders of domestic ani- 
 mals. Manifestly the more inferior the foundation mother 
 stock, the greater will be the improvement when mated to 
 a pure-bred registered sire. A few generations will often 
 suffice to produce " high-grade " cattle, horses, sheep or 
 swine that will possess most of the valuable qualities 
 which have commercial value. For commercial or eco- 
 nomic purposes, the high-grade beef animal may be as 
 valuable as the pure-bred. A high-grade dairy cow will 
 often produce as much milk and butter as the registered 
 cow. For breeding purposes, the pure-bred registered 
 animal is far superior. The grade does not transmit its 
 qualities with certainty. One object of pure breeding 
 is to develop the quality of prepotency, and this is accom- 
 plished by long years of most careful selection and mat- 
 ing. The grade animal cannot possibly possess the 
 quality of prepotency to the same extent as the pure- 
 bred form, hence it follows that even if the grade does 
 exhibit a high degree of individual merit, this is no evi- 
 dence of ability to transmit the same qualities to the 
 offspring. A high degree of individual excellence in a 
 pure-bred registered animal is more certain to be trans- 
 mitted, and for this reason the registered animal of high 
 merit is often held by the experienced breeder at values 
 which seem beyond any real economic basis. 
 
 229. Cross-breeding to increase fertility. — Some ani- 
 mals are infertile when bred to other individuals of their 
 
246 THE BREEDING OF ANIMALS 
 
 own breed. This is particularly the case if the two ani- 
 mals mated are the result of long-continued in-breeding 
 and are themselves also near of kin. 
 
 In the instance of in-breeding pigs by J. Wright already 
 cited, the seventh generation resulting from close in- 
 t)reeding consisted of one sow. This sow was infertile 
 when bred to her sire, but bred readily with an unrelated 
 boar. Darwin cites numerous instances of increased 
 fertility due to crossing. Mr. Eyton,^ a breeder of Grey 
 Dorkings, found it necessary to increase the prolificacy 
 and increase the size of his in-bred stock by cross- 
 ing. Bates,^ the great breeder of Shorthorn cattle, bred 
 closely in-and-in for thirteen years, but then found 
 it necessary to " infuse fresh blood, not to improve 
 the form of the animals but on account of lessened 
 fecundity." 
 
 Bloodhounds ^ closely in-bred lost their fertility, which 
 was restored by a single cross. 
 
 Many plants are infertile unless cross-fertilized with 
 the pollen of another variety. 
 
 230. Cross-breeding to increase size and restore 
 constitution. — The tendency of in-breeding to decrease 
 the size is promptly corrected by cross-breeding. " The 
 good effects of a cross are at once shown by the greater 
 size of the offspring." 
 
 It is the common experience of breeders that highly 
 improved strains of cattle, hogs or sheep sometimes show 
 a refinement or delicacy of constitution which in a measure 
 interferes with the economic value. In such cases a sud- 
 den out-cross to another equally valuable strain may 
 
 ^ Darwin, "Animals and Plants under Domestication," vol. 
 II, p. 105. 
 2 Ibid. 
 ' Loc. cit. 
 
^>. 
 
 y >. 
 
 
 
CROSS-BREEDING 247 
 
 quickly correct any tendency to inferior size or weakened 
 constitution. Not only are in-bred animals benefited 
 in certain definite qualities by crossing, but breeds and 
 families which have not suffered in any way from in-breed- 
 ing are sometimes improved in size, vigor and fertility 
 by crossing. 
 
 231. Crossing and heredity. — As in-breeding tends 
 to simplify the germ-plasm and strengthen the powers of 
 transmission, so cross-breeding tends to weaken the 
 prepotency and complicate the elemental constitution 
 of the hereditary substance. Crossing has a tendency 
 to break up established characters. It destroys com- 
 binations of characters which have long existed in the 
 strain and which under systems of pure breeding have 
 behaved in a manner like unit characters in trans- 
 mission. The result of crossing pure-bred animals is 
 often to destroy the results of generations of careful 
 breeding and selection. 
 
 232. First cross an improvement. — The cross-bred 
 offspring of pure-bred parents often show an improvement 
 over either of the parents. This superiority may be 
 exhibited not alone in increased fertility and more vigorous 
 constitution, but also in the very qualities which char- 
 acterize the parents. A cross between animals belong- 
 ing to distinct breeds may be a better beef animal than 
 either parent. The Scotch farmer breeds the Aberdeen 
 Angus cow to a white Shorthorn bull. The offspring is 
 the well known " blue gray " which is highly prized by 
 the feeder and in the fat cattle market commands a 
 premium over the pure-bred animals of either breed. 
 The fat cattle exhibitions of the world have not infre- 
 quently given the highest prizes of the show to cross- 
 bred animals. (See Plate XVI.) 
 
248 THE BREEDING OF ANIMALS 
 
 But when it is attempted to perpetuate the superior 
 qualities of the cross-bred animal by breeding, disappoint/- 
 ment invariably results. The second cross resulting 
 from the mating of two cross-bred animals may be totally 
 unlike either of the immediate parents or of the original 
 pure-bred forms. Crossing, therefore, is not a method to 
 be employed for rapid improvement or for fixing desir- 
 able qualities. It is opposed to in-breeding which does 
 increase prepotency and is the most rapid method known 
 of fixing desirable characters. 
 
 233. Cross-breeding as a cause of variation. — The 
 fact that crossing disturbs the balance of characters and 
 brings about recombinations in the germ-plasm gives it a 
 peculiar value in causing variations to appear. The 
 breeder who is working with pure-bred animals which owe 
 their purity of breeding to a long period of careful selec- 
 tion by skillful breeders cannot hope to cause any great 
 degree of improvement. Pure-bred animals are already 
 improved. About all any breeder working with pure- 
 bred animals can do is to select out the highly desirable 
 strains from those of lesser value already in the breed. 
 But as Johanssen has shown, there are very definite limits 
 beyond which the improvement of pure lines cannot go. 
 Marked improvement must come through variation. 
 Crossing is a common cause of variation. Variations 
 which appear as the result of crossing may be desirable 
 or undesirable. They may be relatively unimportant 
 or they may be in the nature of a valuable mutation. 
 Such valuable mutations may be perpetuated by in -breed- 
 ing and a new and valuable quality sometimes secured 
 in this way. This method is not practical for breeders 
 of registered live-stock under present conditions, but has 
 been of great service to the breeders of plants. 
 
Plate XVII. — Upper. — Half-blood buffalo (bison) heifer. The 
 hybrids are larger than either parent. Lower. The bull on the left is 
 five-eighths buffalo (bison) and three-eighths Hereford. The animal on 
 the right is a three-quarter blood buffalo. These hybrids are frequently 
 sterile. 
 
CROSS-BREEDING 249 
 
 234. Crossing species. — Many species may be suc- 
 cessfully crossed. Some of these crosses are of great 
 economic value, as the cross between the mare and the jack. 
 The number of successful crosses between animal species 
 is not large. Such unions are difficult to make and 
 generally sterile. When such crosses are possible and 
 the union is fertile, the offspring is generally partially 
 or wholly sterile. Some of the successful crosses which 
 have been reported are the sheep and goat, horse and ass, 
 horse and zebra, cattle and yak, cattle and bison, brahmin 
 and domestic cow, game cock and guinea fowl, domestic 
 fowl and pheasant, dog and wolf, and dog and fox. 
 
 235. Crossing bison and cattle. — A most interesting 
 experiment in cross-breeding between the bison and 
 domestic cattle is reported by Mossom M. Boyd.^ The 
 hybrid offspring from Hereford dams and bison sire were 
 very uniform, all having white faces, were larger than 
 the bison and much smoother, broader and deeper than 
 the sire. Great difficulty was experienced in making 
 the first cross from the excessive secretion of the amniotic 
 fluid. This difficulty caused many deaths. The per- 
 centage of males from the first cross was very small. 
 Among forty-five hybrids, only six were males. Of these 
 three died at birth, one died in less than twenty-four hours 
 after birth, one proved barren, and the last male was 
 killed before determining his fertility. Charles Good- 
 night of Texas reports ^ that " no male calves have ever 
 been born ; cows conceiving them either suffer abortion 
 or die, hence only get heifer calves and only a small per 
 cent of them." The hybrids produced their first calves 
 at an average age of five years (Plate XVII). 
 
 1 Boyd, Journal of Heredity, 1914, p. 189. 
 
 2 Goodnight, Journal of Heredity, 1914, p. 199. 
 
250 THE BREEDING OF ANIMALS 
 
 Three-quarter blood bisons from pure bisons, bulls and 
 hybrid cows were similar in form and color to the bison ; 
 one cross-bred from a half Hereford dam had a white 
 face. One-quarter blood bisons from hybrid dams and 
 Hereford and Aberdeen Angus bulls were uniform in 
 conformation but varied in color. The three-quarter 
 bloods closely resembled the bison, while the one-quarter 
 bloods could not readily be distinguished from domestic 
 cattle. From twenty-four hybrid cows, only three were 
 regular breeders and fifteen were barren. From twelve 
 one-quarter blood bison cows bred to domestic animals, 
 seven were fully fertile, four were irregular breeders, and 
 one was barren. One out of four of the three-quarter 
 blood bison cows was barren. The term '' cattalo " 
 is used by Boyd to designate the third generation. When 
 both parents are of mixed blood, the cattaloes are in many 
 respects superior to ordinary domestic cattle, being hardier 
 and much less subject to disease. Cattaloes with a high 
 percentage of bison blood are probably immune from 
 Texas fever and blackleg. The cattalo grows to a greater 
 weight than domestic cattle. Goodnight ^ says, " More 
 of them can be grazed on a given area. They do not 
 run from Heel Flies nor drift in storms. They rise on 
 their fore feet instead of their hind feet. They never 
 lie down with their backs down hill, so they are able to 
 rise quickly and easily." 
 
 It seems entirely probable that a new breed will be 
 added to the list of domestic cattle, and if this result is 
 achieved, it will be one of the very few authentic cases of 
 the establishment of a new breed by crossing species. 
 
 236. The mule hybrid. — The most widely distributed 
 and most useful hybrid known is the mule, which is pro- 
 
 ^ Goodnight, Journal of Heredity, 1914, p. 199. 
 
CROSS-BREEDING 251 
 
 duced by crossing the domestic mare to the jack. In 1915 
 there were 4,479,000 mules in the United States. This 
 was more than one-fifth of the total number of horses 
 in the country at the same time. The production of 
 mules has increased at a more rapid rate than horses, and 
 the use of mules is becoming more extensive. The mule 
 hybrid is a remarkable example of the practical advantages 
 which follow a particular cross. This animal is more 
 hardy and enduring than either parent. As compared 
 with the horse, the mule is longer-lived, less subject to 
 disease or injury, and more efficient in the use of food. 
 The mule can be safely put to work at a younger age, will 
 thrive on coarser feed, and seems to be much better able 
 to avoid many dangers which menace the usefulness of 
 the horse. The mule will perform more arduous labor 
 on less food. The mule will endure the heat of southern 
 latitudes more successfully than the horse and is there- 
 fore a popular draft animal in the South. 
 
 The cross between the mare and jack is readily accom- 
 plished and the union is perfectly fertile. The conforma- 
 tion of the mule more closely resembles that of his sire. 
 The ears are long, feet long and narrow, withers sharp, 
 mane and tail scanty, and the voice a bray like the jack. 
 The mule is sterile. A few cases of supposed fertility of 
 mare mules have been reported, but the writer has investi- 
 gated several apparently reliable reports and has never 
 found an authentic case of a fertile mule. Most of the 
 erroneous reports of fertile mules have apparently arisen 
 from the not infrequent cases of mare mules which have 
 been observed suckling mule foals. The milk glands of 
 mare mules have been known to function as the result 
 of the stimulation afforded by a suckling foal. A case 
 of a mare mule giving milk was reported to the writer 
 
252 THE BREEDING OF ANIMALS 
 
 by L. O. Swarner of Boonville, Missouri, in 1913. This 
 mare was six years old and at the time had been giving 
 milk for five weeks. The milk glands had not been stimu- 
 lated in any way, but the milk " streamed " from the 
 udder. It is also of interest to know that this mare mule 
 showed unmistakable evidences of what in the ordinary 
 mare would be regarded as complete sexuality. She 
 came in heat regularly. The mule was bred frequently 
 when in season to both the stallion and jack, but failed 
 to conceive. A sample of the milk was analyzed by the 
 Chemical Department and found to contain 2.46 per cent 
 protein, 5.8 per cent sugar, 1.45 per cent fat, and .4 per 
 cent ash. (See Plate III.) 
 
 The mare mules apparently have all the essential 
 organs of reproduction and come in heat with considerable 
 regularity. The horse mule also has the essential sexual 
 organs well developed and his sexual instincts are so well 
 developed that castration of young mules is universally 
 practiced. The cause of sterility in the horse mule is not 
 due to a failure to develop spermatozoa, but the sperm- 
 cells are imperfect. In some cases the sperm-cells lack 
 the tail or fl^gellum. 
 
 237. The hinny hybrid. — The reciprocal cross between 
 the jennet and the stallion is accomplished without 
 difficulty and the union is very fertile. The hybrid from 
 the cross is called a hinny. Some authorities have held 
 that the hinny resembled the horse much more closely 
 than the mule, but this is denied by most practical breeders. 
 The hinny is not commercially important as the jennet 
 is too valuable for the production of jacks to be used for 
 crossing. The hinny is sterile. (See Plate XVIII, upper.) 
 
 238. Crossing the horse and the zebra. — The horse 
 and zebra have been successfully crossed by Ewart of 
 
Plate XVIII. — Upper. A five-year-old hinny. Dam a jennet, 
 sire a Percheron stallion. Lower. Sheep-goat hybrid. 
 
CROSS-BREEDING 253 
 
 Edinburgh, Scotland, the United States Department of 
 Agricuhure and many others. The zebra-horse hybrid 
 is easily domesticated and can be successfully broken 
 to harness. The first cross is not so easily made as that 
 between the jack and the mare but is not impossible or 
 extremely difficult. The zebra possesses a much smoother, 
 finer and more horse-like form than the ass, and the 
 zebra hybrid therefore is possessed of more quality and 
 " finish " than the mule. This hybrid should prove 
 valuable, particularly in those regions where the " tsetse " 
 fly is fatal to horses but not to zebras and probably not 
 to the zebra hybrids. 
 
 239. Crossing cattle and. zebu. — Many crosses have 
 been made between the zebu and European cattle and 
 between the zebu and the cattle of Tunisia. The first 
 cross in practically all of the experiments seems to have 
 been successful. 
 
 The cross-bred zebu is resistant to Texas fever and 
 anthrax and is not seriously inconvenienced by foot and 
 mouth disease.^ In Brazil ^ the zebu cross is popular. 
 It is claimed that the cross-bred zebu is more prolific and 
 that these animals herd together better than the ordinary 
 domestic cattle. The zebu hybrids are less tractable 
 and docile than domestic cattle, but are very active and 
 enduring draft animals. « 
 
 Because of the disease-resisting qualities of the zebu, 
 its prolificacy, adaptability to hot climates and general 
 hardiness, Nabours ^ is of the opinion that this type of 
 cattle may yet become an important breed in the United 
 States. 
 
 1 Roederer, Journal of Heredity, 1915, p. 201. 
 
 2 Hunnicutt, Journal of Heredity, 1915, p. 195. 
 
 * Nabours, American Breeder's Magazine, 1913, p. 38. 
 
254 THE BREEDING OF ANIMALS 
 
 240. Sheep-goat hybrid. — The cross between the 
 sheep and goat has been successful in a number of in- 
 stances. Spillman reports such a hybrid belonging to E. 
 Armand of Monett, Missouri. (See Plate XVIII, lower.) 
 
 The covering of the body of this hybrid was generally 
 goat hair, but the back was covered with '' shaggy wool." 
 " This hybrid is a female and appears to be infertile, but 
 not absolutely so, for it has once produced a half-grown 
 foetus." 1 
 
 1 Spillman, Journal of Heredity, 1913, p. 69. 
 
CHAPTER XIII 
 
 DEVELOPMENT 
 
 The qualities which an animal possesses are due in 
 the first place to inheritance and in the second place to 
 the manner in which the inherited qualities have been 
 developed. An animal cannot develop beyond the capaci- 
 ties which have come to it through the germ-plasm. It 
 is also true that the capacities which are inherited cannot 
 benefit the individual unless they are developed through 
 a favorable environment. It is seldom that an animal 
 realizes fully the possibilities for development which are 
 inherent in the germ-plasm. The carefully bred beef 
 animal inheriting those valuable qualities of early ma- 
 turity, broad, deep and rounded form, rugged constitution 
 and quiet temperament, with a distinct tendency to lay 
 on fat when food is abundant, may completely fail to 
 exhibit these inborn characters and actually display the 
 form and characteristics of the unimproved animal if it 
 has been surrounded by conditions which are unfavor- 
 able for the development of these special qualities. The 
 highly improved dairy cow with the inherited capacity 
 to produce enormous quantities of milk and butter may 
 never rise above mediocrity if she is not supplied with 
 food and her milking functions intelligently developed. 
 In the selection of animals for improvement, the skillful 
 breeder can never know what results he has achieved 
 until the products of his skill have been fully developed. 
 
 255 
 
256 THE BREEDING OF ANIMALS 
 
 It is not too much to say that no man can be a successful 
 breeder who is not also skillful in developing his animals. 
 Thus, in practice, development becomes supremely im- 
 portant and throughout the history of animal-breeding 
 has been only second in importance to heredity itself. 
 A satisfactory treatment of development in all its phases 
 as related to animal husbandry would require a volume, 
 and as the chief purpose of this work is to consider how 
 the inherited capacities of animals finally appear as definite 
 characters in the germ-plasm, only a limited reference 
 can be made to developmental phases of chief importance 
 to the animal-breeder. 
 
 241. Growth. — From the fertilization of the egg until 
 the full development of the mature individual, the animal 
 increases in volume and changes in form. This increase 
 and change of form is called growth. The final size of 
 an animal is determined by the rate of growth and the 
 length of the growth period. The guinea pig and rabbit 
 come to full maturity at about the same age, but the rabbit 
 is larger because its rate of growth is more rapid. The 
 rate of growth in the rabbit and man is about equal, 
 but man is much larger at maturity because the period 
 of growth is much longer.^ 
 
 242. The growth impulse. — The young of any species 
 tend to develop and grow in accordance with the normal 
 habit of the species. This applies in a special sense to 
 the skeletal system. Even in the absence of a sufficient 
 supply of feed and other favorable conditions, the young 
 animal displays a remarkable physiological impulse to 
 continue to increase in the skeletal parts. ^ Animals fed 
 
 1 Morgan, "Experimental Zoology," p. 245. 
 
 2 Waters, "Capacity of Animals to Grow under Adverse 
 Conditions." 
 
DEVELOPMENT 257 
 
 on a limited ration will continue to increase in height, 
 length of body, and other parts of the skeleton, at the 
 same time becoming thinner and thinner in flesh. Even 
 during starvation the same tendency is apparent. This 
 fact has been noted by H. Aron,^ who found that while 
 fasting, the skeleton grows at the expense of the other 
 body tissues. 
 
 243. Factors influencing growth. — The chief factors 
 influencing growth in the domestic animals are food, 
 heat, light, age, gestation and lactation. The chief 
 condition influencing growth in normal animals is the 
 food supply. 
 
 244. Growth and food supply. — While it is true that 
 the animal may for a limited time add to its tissues when 
 food is insufficient in either quantity or quality, it is 
 also tru^ that a long-continued deficiency in the food 
 supply of young growing animals will invariably check 
 their growth. The check to growth in such cases may 
 be only temporary, or it may result in permanently decreas- 
 ing the normal size of the mature animal. (See Plates XIX 
 and XX.) 
 
 245. Capacity to grow. — The young animal that is 
 stunted as a result of insufficient food does not lose the 
 capacity to grow. The organism seems to be able to 
 continue to function and maintain a certain equilibrium. 
 If later a greater abundance of food is supplied, the rate 
 of growth may be reestablished. If after a period of 
 partial starvation the food supply is abundant, the rate 
 of growth may for a time be even more rapid than before. 
 That the capacity of an animal to grow is not destroyed 
 by stunting is shown by the results of an investigation 
 at the Missouri Experiment Station by Waters and 
 
 1 H. Aron, Exp. Sta. Record, vol. 24, p. 765. 
 
 s 
 
258 THE BREEDING OF ANIMALS 
 
 P. F. Trowbridge.^ These investigators fed a beef steer 
 from the age of three months to thirty-eight months old. 
 From three to twelve months of age the animal was fed 
 on a maintenance ration (Plate XXI). An attempt was 
 made to feed the young calf in such a way that it would 
 neither gain nor lose in live weight. At the beginning of 
 the period (three months old) (Plate XXI, upper left) 
 the animal weighed 175 pounds; at twelve months 
 (Plate XXI, upper right) the animal weighed 212 pounds. 
 Another animal similar in every way at the beginning 
 was fed a full ration of nutritious feed. The latter 
 animal increased in weight from 200 pounds at four 
 months (see Plate IX) to 875 pounds at 336 days of 
 age (Plate VIII, upper). The animal fed on a sparse 
 ration continued to increase in height, length of body, 
 size of bone, and other skeletal measurements but lost 
 constantly in fat and gradually became leaner and thinner. 
 At the end of the twelve months the steer was much 
 emaciated and showed symptoms of starvation. From 
 the standpoint of the practical feeder, the animal was. 
 clearly stunted in its growth, and in the opinion of many 
 breeders he had lost very greatly in his capacity to gain 
 in live weight and to do so on what would be regarded as 
 a normal amount of food. In other words, his economic 
 value for the production of beef was very greatly dimin- 
 ished. After twelve months the animal was given a 
 gradually increasing amount of nutritious food until 
 he was consuming a normal ration. The animal rapidly 
 improved in condition and at twenty-four months (Plate 
 XXII) had reached a total weight of 1055 pounds, a total 
 gain of 842 pounds in twelve months. This gain was not 
 expensive in that a large amount of feed was required to 
 
 1 Missouri Experiment Station, unpublished data. 
 
Plate XXI. — Starvation does not destroy capacity to grow. Upper 
 left. Steer 529 weighing 175 pounds at age 96 days. Ration greatly 
 restricted until age 365 days. Upper right. Steer 529 weighing only 
 200 pounds at age 310 days. Resulting from feeding greatly restricted 
 ration. Lower. Same animal at age 38 months and weighing 1487 
 pounds. 
 
a >.^ 
 
 fed -t^ s 
 
 c3 
 
 I— I t3 
 
 o3 c3 ^M 
 
 ^ M 
 
 ►J ^ g bc 
 
DEVELOPMENT 259 
 
 produce a pound of gain, but on the other hand the gain in 
 live weight was accompHshed by feeding only five and six 
 one-hundredths pounds of grain and two and four-tenths 
 pounds of hay for each pound of gain. The steer that 
 had been fed generously for the first twelve months of 
 its life gained only 500 pounds during the period in 
 which the stunted one had gained 842 pounds. In the 
 production of the 500 pounds the full-fed steer had con- 
 sumed nine and eight-tenths pounds of grain and four 
 and two-tenths pounds of hay for each pound of gain in 
 live weight. Over forty per cent less feed was required by 
 the stunted animal for each pound of increase in live 
 weight. Not only did the stunted animal not lose 
 its capacity to grow, but in certain respects its growth 
 processes were accelerated during the period covered 
 by this experiment as a result of its difficult struggle 
 for existence during the first twelve months of its 
 life. 
 
 246. Growth and the cell. — Increase in the size of 
 animals which follows growth is due to a multiplication 
 of cells and not to an increase in their size. The size 
 of cells varies between rather narrow limits. The larger 
 size of some animals is not due to larger cells in their 
 organization but to a larger number of cells. It is also 
 true that the cells in any individual animal vary but 
 little in size. The increase in size of any part of an animal 
 is due, therefore, to an increase in the number of cells 
 and not to an expansion of cells already formed. It is 
 true, of course, that certain minor exceptions to this rule 
 are to be observed. The nerve cells vary in size with the 
 size of the animal. The nerve cells of an ox are much 
 larger than those of the pig. The frog has very large 
 cells, while the starfish is composed of small cells. But 
 
260 THE BREEDING OF ANIMALS 
 
 a large frog differs from a small frog in the number of 
 cells, not in their size. Each individual animal begins its 
 existence as a single cell. Through cell division the em- 
 bryonic organism rapidly increases in size until maturity 
 is reached. The rate of growth of the individual is most 
 rapid during the very early stages in the development of the 
 embryo. The rate of growth decreases gradually from this 
 time until full maturity, when nominally growth ceases. 
 
 247. When the growth impulse is strongest. — The 
 growth impulse is strongest in the animal while still exist- 
 ing in the uterus of the mother. After birth the growth 
 continues less rapidly, but is still very rapid when compared 
 with the increase in size during the later months of the 
 growth period. It is for this reason that the period of 
 gestation is so fundamentally important in the life of the 
 animal. During this period of exceedingly rapid increase 
 in size and development of the vital organs and other parts 
 of the body, any abnormal condition which interferes 
 with the normal requirements of the unborn animal may 
 cause arrested development and result in seriously retard- 
 ing the growth or permanently crippling the individual. 
 It is undoubtedly true that during this period the prac- 
 tical breeder may through skillful feeding and care ma- 
 terially influence for good or evil the development of the 
 valuable characters of the domestic animals. 
 
 248. Development of the foetus. — The development 
 of the fertilized egg through the embryonic stages of the 
 life of the mammalian animal is influenced by a number 
 of conditions which may have a profound influence upon 
 the material well-being of the future mature animal. 
 Some of these influences are as yet obscure and not well 
 understood, while others are more clearly determined 
 and their effects more easily recognized. 
 
DEVELOPMENT 261 
 
 The development of the foetus is influenced by heredity, 
 and the physiological environment of the pregnant mother. 
 Among the latter are the general health or well-being 
 of the mother, age, the quantity and quality of the food 
 supply and mental impressions. 
 
 249. Heredity and foetal development. — The inherited 
 tendencies of an animal are exhibited from the very be- 
 ginnings of its existence in the fertilized egg-cell. Its foetal 
 development, therefore, must be influenced to a certain 
 extent by those inherent determiners which have come to 
 the fertilized egg-cell from the male parent. The size of 
 the foetus at various stages of development then would be 
 determined, not alone by the maternal heredity and en- 
 vironment, but also by the inherited characteristics which 
 have been acquired through the male. At the same time 
 it is probable that the maternal environment has a much 
 more important influence on the foetal development than 
 its paternal hereditary tendencies. If it were otherwise, 
 serious consequences might follow the mating of smaller 
 females to much larger males among the domestic animals. 
 
 Pony mares weighing 700 to 900 pounds are not infre- 
 quently mated with large stallions of the draft breeds 
 weighing 2000 pounds or more. Under these conditions 
 the foetus is not as much larger than the normal foetus 
 of the mother as might be expected from the much greater 
 size of the stallion. Small burro mares weighing 400 
 or 500 pounds have been artificially inseminated with 
 the sperm of Percheron and other heavy draft stallions. 
 The growth of the foetus in this case is undoubtedly some- 
 what greater during the normal period of gestation than 
 the growth of a pure burro foetus, but the increased size 
 is not a mean between the normal size of a Percheron and 
 a burro foetus, but is much smaller. 
 
262 
 
 THE BREEDING OF ANIMALS 
 
 Relation of Weight of Dam to Birth Weight of 
 
 Lamb 
 
 Weight op Dams 
 
 Number 
 
 OF 
 
 Single 
 Lambs 
 
 Average 
 
 Birth 
 
 Weight 
 
 OF 
 
 Single 
 Lambs 
 
 Number 
 
 OF Twin 
 
 Lambs 
 
 Average 
 
 Birth 
 
 Weight 
 
 OF Twin 
 
 Lambs 
 
 Average 
 Birth 
 
 Weight 
 OF All 
 Lambs 
 
 Below 90 lbs. . . 
 90 to 100 lbs. . 
 100 to 110 lbs. . 
 110 to 120 lbs. . 
 120 to 130 lbs. . 
 
 8 
 
 6 
 
 14 
 
 12 
 
 13 
 
 7.2 lbs. 
 7.4 lbs. 
 
 8.6 lbs. 
 
 8.7 lbs. 
 8.9 lbs. 
 
 8 
 20 
 10 
 
 6.4 lbs. 
 7.2 lbs. 
 7.6 lbs. 
 
 7.2 lbs. 
 
 7.4 lbs. 
 
 7.5 lbs. 
 7.9 lbs. 
 
 8.3 lbs. 
 
 250. Birth weight of lambs. — The author/ investi- 
 gating the birth weight of lambs from grade Merino ewes 
 bred successfully to Shropshire, Hampshire and Merino 
 rams, found that the size of lambs at birth is primarily 
 determined by the nutrition of the foetus while carried 
 in the uterus of the mother. The nutrition of the foetus 
 will of course be determined entirely by the physiological 
 condition of the mother during gestation. This is shown 
 in one test in which the birth weight of twenty-nine lambs 
 sired by two heavy rams averaging 237 pounds in weight 
 was 8.16 pounds. The average weight of two other 
 rams of the same breeds was 142^ pounds. The two 
 lighter rams sired twenty-five lambs from the same ewes, 
 or ewes of the same type. The average birth weight of 
 these lambs was 8.75 pounds. The weight of the sires 
 in this case seemed to have little influence on the weight 
 of lambs at birth. In attempting to discover the real 
 factors determining the growth of the foetus as measured 
 by the weight of lambs at birth, it was found that the 
 
 IF. B. Mumford, "Some Facts Influencing the Weight of 
 Lambs at Birth," Bulletin 53, Missouri Experiment Station. 
 
DEVELOPMENT 263 
 
 nutritive condition and weight of the mothers had an 
 important influence on the development of the foetus. 
 This fact is shown in the table on page 262. 
 
 Summarizing the results of four years' work, the author 
 says/ ^' We must conclude from the exhibit here made, 
 comprising the results of 61 births, that the weight of 
 the mother has a direct influence upon the birth weight 
 of the offspring and that in general the lambs having a 
 heavier weight at birth are produced from the larger 
 ewes." 
 
 251. Effect of protein and ash in ration on fcetal 
 development. — The development of the foetus may be 
 materially influenced by the ration given to the mother 
 during pregnancy. Evvard ^ has shown that if pregnant 
 sows are fed a ration poor in protein, the pigs are smaller 
 at birth. Not only were the offspring smaller at birth, 
 but they were weaker and the death rate greater. The 
 first investigation was made with young sows in 1910- 
 1911. These were fed the rations indicated in the table 
 on page 264 for a considerable period. The results are 
 summarized in the table. 
 
 ^ " The basal ration was corn alone. Corn we know is 
 quite deficient in protein (the zein which comprises prac- 
 tically 58 per cent of said protein is peculiarly lacking in 
 two quite important amino acids, namely, tryptophane 
 and lysine) and calcium. It is somewhat surprising to 
 know that calcium comprises practically two-thirds as 
 much of the body substance as does nitrogen, the basal 
 element of protein." 
 
 " Note that the supplemented rations not only pro- 
 duced larger but stronger pigs at birth. A studied survey 
 
 ^ Mumford, loc. ciL, p. 176. 
 
 2 Evvard, Iowa Academy of Science, Report 1913, p. 326. 
 
264 
 
 THE BREEDING OF ANIMALS 
 
 of the above figures shows most clearly that even though 
 the carbohydrates were limited, as in the meat meal 
 lots, the increase in protein and ash was such as to mark- 
 edly influence the size and strength of the new-born pigs. 
 That clover and alfalfa should also have a marked effect 
 is logical because these hays are leguminous in character, 
 run high in protein and calcium, and also have an alkaline 
 ash which is probably beneficial." 
 
 Effect on Offspring of Feed Fed Pregnant Swine ^ 
 Gilts. — Five in a Lot, 1910-1911 
 
 Gilt Record 
 
 Offspring Record 
 
 
 a 
 O 
 
 Feed Daily 
 
 .1 
 
 
 Per cent Vigor 
 
 
 
 
 
 
 
 
 
 Pregnancy Ration 
 OP Gilts 
 
 > 
 
 < 
 
 Shelled 
 Corn 
 Lbs. 
 
 Supple- 
 ment 
 Lbs. 
 
 6i^ 
 
 < 
 
 Av. wt. 
 
 born P 
 
 Lbs. 
 
 a 
 B 
 
 
 0) 
 
 Q 
 
 Corn Only . . . 
 
 .354 
 
 3.65 
 
 None 
 
 7.6 
 
 1.74 
 
 68 
 
 16 
 
 16 
 
 
 
 Corn +Meat Meal 
 
 
 
 
 
 
 
 
 
 
 (Light) . . . 
 
 .582 
 
 3.21 
 
 0.127 
 
 7.4 
 
 2.01 
 
 92 
 
 5 
 
 3 
 
 
 
 Corn+MeatMeal 
 
 
 
 
 
 
 
 
 
 
 (Heavy) . . 
 
 .635 
 
 2.75 
 
 0.432 
 
 8.8 
 
 2.23 
 
 93 
 
 5 
 
 2 
 
 
 
 Corn + Clover . . 
 
 .528 
 
 3.67 
 
 0.302 
 
 6.4 
 
 2.21 
 
 94 
 
 
 
 6 
 
 
 
 Corn+Alfalfa . . 
 
 .627 
 
 3.74 
 
 1.106 
 
 7.6 
 
 2.29 
 
 89 
 
 8 
 
 
 
 3 
 
 A similar test with older (^-earling) sows confirmed the 
 conclusions from the first investigation. In the latter 
 trial there was evidence that animal protein supplied in 
 meat meal was more efficient than vegetable protein 
 supplied in linseed oil meal. 
 
 252. High calcium rations for pregnant swine. — The 
 ordinary rations fed to farm animals in most localities 
 
 1 Evvard, Iowa Academy of Science, Report 1913, p. 326. 
 
DEVELOPMENT 265 
 
 are known to be deficient in calcium. This is particu- 
 larly true when, as in the case of swine, the rations are 
 chiefly composed of grain with a relatively small propor- 
 tion of roughage. It is a popular notion that feeding 
 pregnant farm animals a high calcium ration will cause 
 the skeletal systiem of the foetus to develop even beyond 
 what may be regarded as normal. As a result of this 
 greater development of the skeleton, it has been alleged 
 that the mother may sometimes have serious difficulty 
 in expelling the foetus. Some confirmation of this belief 
 is apparently found in the work of Evvard already de- 
 scribed. But in this investigator's trials a ration abnor- 
 mally deficient in calcium and protein is compared with 
 normal rations. Adding an excess of calcium to a normal 
 ration may not necessarily increase the size or change the 
 composition of the foetus. In this respect we know that 
 similar changes in the ration do not change the composi- 
 tion of the milk. At the Wisconsin Experiment Station, ^ 
 Hart, Steenbock and Fuller compared normal rations 
 with a high calcium ration fed to pregnant swine. Eight 
 Poland China sows were fed in lots of tw^o each. Three 
 lots were fed on a high calcium ration by the addition of 
 calcium carbonate, calcium phosphate (floats) and alfalfa. 
 One lot was fed a normal standard ration known to be 
 adequate for pregnant swine. These rations were fed 
 throughout the gestation period. Although the calcium 
 rations contained five times the amount of this mineral 
 present in the normal ration, there was no evidence 
 that the skeleton of the foetus was influenced in 
 any degree. The authors in summarizing their results 
 
 ^ Hart, Steenbock and Fuller, " Calcium and Phosphorus 
 Supply of Farm Feeds and their Relation to the Animal's Re- 
 quirements," Wisconsin Research Bulletin No. 30. 
 
266 THE BREEDING OF ANIMALS 
 
 conclude that " High calcium rations, as compared with 
 low calcium rations, had no effect whatever during a 
 single gestation period on the size or calcium content of 
 the skeleton of the foetus. The skeleton is not increased 
 in any dimension by a wide variation in the amount of 
 calcium fed the mother." 
 
 253. Size and vigor of foetus as influenced by corn and 
 wheat rations. — The particular rations fed to breeding 
 animals may profoundly influence the character of the 
 foetus. It is not enough that the prospective mother 
 should receive a ration containing the right proportions 
 of protein, carbohydrate and mineral substances, but 
 these minerals must be of the kind of substances which 
 are known to satisfy the nutritive necessities of the ani- 
 mal. A most interesting demonstration of this fact was 
 made possible through the valuable work of Hart,^ McCol- 
 lum, Steenbock and Humphrey at the Wisconsin Experi- 
 ment Station. In May, 1907, these investigators began 
 feeding four heifers a ration of corn meal, corn stover and 
 gluten feed, all corn products. Another group of four 
 was fed wheat meal, wheat straw and wheat gluten, nutri- 
 ents derived entirely from the wheat plant. The mate- 
 rials supplied in each ration were proportioned in such a 
 manner as to furnish each group of animals a well- 
 balanced ration in accordance with the accepted feeding 
 standards. The feeding continued for two years and 
 accurate records were kept of feed consumed, gains in 
 live weight, and physiological condition of all animals in 
 the experiment. 
 
 1 Hart, McCoUum, Steenbock and Humphrey, "Physio- 
 logical Effect on Growth and Reproduction of Rations Balanced 
 from Restricted Sources," Research Bulletin No. 17, Wisconsin 
 Experiment Station. 
 

 
 ■X- 
 
 
 ■■>.--s-*^-^H?ij 
 
 .-5 - r: 
 
 .■^. 
 
 "/IS^'^'^* 
 
 -A^ •-. 
 
 --— -«„-^_ '>, , 
 
 ..,_. r -^ 
 
 -^ T_„..^— ' 'C. ' ■ -v 
 
 
 ' J : '■ 
 
 in 
 
 ^' '" ' "■"■ 
 
 - . -*^"/ ^■* 
 
 
 1 ' 
 
 N «.^. ^^^^^m^^IRh 
 
 
 r^ , ^tt 
 
 
 AHflJ^^^H 
 
 
 1 
 
 « 
 
 
 HH 
 
 
 
 
 ~ ^^^1 
 
 P^^ 
 
 
 ^ ^' 
 
 r 
 
 
 
 r^ M 
 
 '». '"C^^^ 
 
 ■,_>..-■ -_.',. 
 
 :v._.:_., v.:«l 
 
 BHfe-L-...:' 
 
 
 hhh 
 
 Plate XXIII. — Upper. A normal healthy cow in good nutritive 
 condition fed exclusively on nutrients derived from Indian corn. 
 Lower. This vigorous, thrifty, well-developed new-born calf from dam 
 (upper) fed exclusively corn ration before and during gestation. 
 
Plate XXIV. — Upper. Unthrifty cow clearly in bad nutritive con- 
 dition due to having been fed wheat products exclusively. Lower. Calf 
 of low vitality from dam (upper) fed exclusively on wheat products, 
 lived only twelve hours. 
 
DEVELOPMENT 267 
 
 The rate of growth of all animals in the two groups 
 was very similar, indicating little difference in the effi- 
 ciency of the rations. But that there was a difference 
 is indicated by the author's description : ^ " The corn-fed 
 animals (Plate XXIII) looked smooth of coat, fuller through 
 the barrel ; and, as expressed by experienced feeders and 
 judges of domestic animals, they were in a better state of 
 nutrition. On the other extreme stood the wheat-fed 
 group with rough coats, gaunt and thin in appearance, 
 small of girth and barrel, and to the practical eye, in rather 
 a lower state of nutrition." But perhaps the most sig- 
 nificant results of this experiment were the effects of these 
 rations on the reproductive functions of the mothers and 
 the vitality of the offspring. The gestation period in the 
 corn-fed mothers was practically normal, while in every 
 case the calves of the wheat-fed group were dropped 
 from two to five weeks before the end of the normal 
 gestation period. The calves from the corn-fed cows 
 were uniformly strong and vigorous and were normal 
 in every respect. The calves from the wheat-fed cows 
 were all born dead or with such low vitality that they 
 soon died. 
 
 The yield of milk from the wheat-fed (Plate XXIV) 
 cows was distinctly below that of the corn-fed group. In 
 discussing the significant results of this investigation the 
 authors say, " These results emphatically show how de- 
 pressing or stimulating the influence of a ration may become, 
 even when it is made up of supposedly normal feed materials 
 and balanced as to ordinary chemical constituents and 
 supply of energy, especially when that ration is continued 
 for a long time. The evidence for the necessity of giving 
 much weight to the physiological influence of the ration, 
 
 1 Loc. cit. 
 
268 THE BREEDING OF ANIMALS 
 
 apart from its digestible protein content and calorific 
 value, is positive." 
 
 254. The permanent effect of retarded growth. — Is 
 the retardation of growth resulting from unfavorable 
 environment a permanent condition? Is it possible per- 
 manently to stunt an animal? This question is one of 
 great interest to the practical breeder of live-stock and 
 the live-stock farmer. The animal is often employed by 
 the farmer for the purpose of disposing profitably of food 
 materials which are of limited value from the standpoint 
 of nutrients and digestibility, but nevertheless have a 
 food value. Teachers and investigators in animal hus- 
 bandry have for a long time taught that any condition 
 which resulted in stunting the young animal, perma- 
 nently affected the mature individual. It has also been 
 claimed by some that the capacity to grow was materially 
 diminished by a stunting period. 
 
 The history of two animals which were fed at the 
 Missouri Experiment Station by P. F. Trowbridge^ is of 
 great interest in attempting to answer this question. One 
 of these animals was given a full ration from birth and 
 the other animal was given a so-called maintenance ration 
 from three months of age to thirteen months. The use 
 of the term maintenance ration in this connection means 
 that it was planned to feed the animal sufficient food to 
 cause it to maintain a uniform body weight. As a matter 
 of fact, the animal added somewhat to his total weight 
 in the ten months of stunting. The tables and pictures 
 (Plate XXV) give a very clear idea of the general results 
 of this trial. The full-fed animal gained rapidly and at 
 the end of fourteen months weighed 956 pounds. The 
 young animal fed merely a maintenance ration weighed 
 
 ^ Missouri Experiment Station, unpublished data. 
 
Plate XXV. — Permanent effect of retarded growth. The animal on the 
 left (No. 527) was fed the maximum amount of a nutritious ration from birth. 
 The animal on the right (No. 529) was starved until twelve months of age 
 and then fed generously to age thirty-eight months. See table on page 269. 
 
DEVELOPMENT 
 
 269 
 
 only 207 pounds at the age of thirteen months. At that 
 time, the animal was emaciated in appearance, showed 
 every symptom of starvation, and was to all appearances 
 very severely stunted in its growth and development. 
 From twelve months to thirty-eight months, the animal 
 fed previously on a maintenance ration was later given a 
 generous ration and gained during that period a total of 
 1280 pounds. The full-fed animal during the same period 
 gained 853 pounds. At the end of the period the animal 
 that was stunted during its early life was over 300 pounds 
 lighter, was apparently somewhat shorter, with finer bones, 
 than the full-fed animal. There was little doubt but that 
 in this trial the early environrnent permanently decreased 
 the size of the adult animal. 
 
 255. Early stunting and the capacity to grow. — It is 
 interesting to know that the capacity to grow was not 
 
 The Permanent Effects of Retarded Growth 
 
 Feed and Weight Records of Two Steers for 24 Months ' 
 
 No. 527 was fed a generous ration until 38 months of 
 age. No. 529 was starved for the first 12 months and 
 then given a full ration until 38 months of age. 
 
 Initial Weight (lbs.) 
 Final Weight (lbs.) 
 Gain during Period 
 Av. Daily Gain . 
 Grain Fed Daily . 
 Hay Fed Daily . . 
 Grain per Lb. Gain 
 Hay per Lb. of Gain 
 Total Grain Eaten 
 Total Hay Eaten . 
 
 Age 1 TO 12 Mos. 
 
 No. 527 No. 529 
 
 165.0 
 
 901.8 
 
 736.8 
 2.046 
 6.926 
 3.578 
 3.384 
 1.748 
 
 2493.44 
 
 1288.12 
 
 175.0 
 
 213.5 
 38.5 
 0.106 
 0.571 
 0.895 
 5.343 
 8.370 
 
 205.73 
 
 322.53 
 
 Age 12 to 18 Mos. 
 
 No. 527 No. 529 
 
 901.8 
 1178.2 
 276.4 
 1.535 
 14.686 
 6.401 
 9.560 
 4.168 
 2643.48 
 1152.18 
 
 213.5 
 
 694.9 
 
 481.40 
 2.674 
 10.030 
 4.840 
 3.750 
 1.813 
 1805.50 
 
 872.83 
 
 Age 12 to 24 Mos. 
 
 No. 527 No. 529 
 
 901.8 
 1401.7 
 499.9 
 1.388 
 13.610 
 5.821 
 9.801 
 4.191 
 4899.86 
 2095.58 
 
 213.5 
 1054.7 
 841.2 
 2.336 
 11.829 
 5.642 
 5.062 
 2.415 
 4258.55 
 2031.13 
 
270 
 
 THE BREEDING OF ANIMALS 
 
 
 
 
 J 
 
 
 
 
 -ti 
 
 
 J 
 
 
 fl 
 
 o 
 
 
 s? 
 
 
 d 
 
 » 
 
 o 
 
 
 m 
 
 
 ^ 
 
 
 CO 
 
 O 
 
 00 
 
 
 o 
 
 |T| 
 
 «0 
 
 
 
 o 
 
 o 
 
 CD 
 
 T— 1 
 
 p 
 
 < 
 
 
 CM 
 
 O 
 
 ft 
 
 03 
 
 H 
 
 s^ 
 
 a 
 
 CD 
 
 W 
 
 
 o 
 
 ^ 
 
 CC! 
 
 s~ 
 
 <t> 
 
 4-3 
 
 fa 
 
 ^ 
 
 rO 
 
 S 
 
 o 
 
 ^ 
 
 a 
 
 
 
 
 o 
 
 
 e*-! 
 
 
 
 03 
 
 fl 
 
 
 fa 
 
 > 
 
 ai 
 
 c3 
 
 fa 
 
 5~ 
 
 1 
 
 i:-! 
 
 
 O 
 
 fl 
 
 H 
 
 O 
 
 
 «*-( 
 
 1^ 
 
 Q^ 
 
 
 o3 
 
 
 C3s 
 
 
 T3 
 
 «4-l 
 
 1^ 
 
 fin 
 
 
 
 1— H 
 
 
 
 
 1 
 
 Eh 
 
 
 
 •a 
 
 e3 
 
 
 f^ 
 
 
 
 05 
 
 
 >0 CD Tt^ '^ 10 
 
 
 
 
 05 -^ t>. CO t^ lO 1-1 
 
 § 
 
 
 ooqoO'-HC^c^r-.iOfNcD 
 
 00 
 
 »o 
 
 iOt^<M"'-5oiTt^t>lcO^(N 
 
 W 
 
 Q 
 
 t^ CO CD Tti t>. 
 
 
 
 ^ 
 
 T-H to CO »0 00 
 
 g 
 
 rH^ q-tH 
 
 i-l 
 
 
 1— I 
 
 
 
 
 
 
 CD CO GO CO ^ 
 
 « 
 
 
 lO ■* 10 CO 1— 1 c: 
 
 ^ 
 
 iM 
 
 Qqq^oq<NrHCDrHoo 
 
 10 
 
 lOLOCJi-Hi-HiOOOCOC^Tt^ 
 
 W 
 
 6 
 
 CD (M CD T-i Oi 
 
 >4 
 
 
 1— 1 00 CD to Oi 
 
 ^r^ CO ^ 
 
 ^ 
 
 
 1—1 
 
 
 
 CD -^ Tti 10 Oi 
 
 CO 
 
 05 
 
 Tti to CO »0 1-H !>. l> 
 
 &4 
 
 10 
 
 TjHoq^(NcDi-;l>T-ji>T^ 
 
 iz; 
 
 cor^-^i-H-^tOi-H-rj^t^Tt^ 
 
 
 
 
 
 1-H CO (N 1-1 r-t CO CM 
 
 § 
 
 '^ 
 
 CO to CM CD Oi 
 
 CO 
 
 
 1—1 1—1 CM 
 
 CO 
 
 
 
 
 
 -^ CO Oi 00 t^ 
 
 t^ 
 
 CD CO to 00 00 00 CO 
 
 
 
 T^OOt^i-iOi-^TfiOiCD 
 
 
 t^t6l>d^TfHo6cDCOCM 
 
 < 
 
 6 
 
 00 CM CO tH 1-1 TtH Oi 
 
 Z 
 
 CD 00 '-H to 00 
 
 
 1-1 i-H CM 
 
 
 
 l:^ CO Tt< CD 
 
 
 
 Oi to CO CO CM 00 
 
 
 05 
 
 tqooCOCDCMoqoO'^iOO 
 
 10 
 
 cor^-^r4coioi>c6toc5 
 
 ^ 
 
 Q 
 
 i-H CO CM r-i CO to 
 
 
 
 ^ 
 
 CM to CO CO to 
 
 S 
 
 CM ^ (-J-'* 
 
 00 
 
 
 1—1 
 
 CO 
 
 
 
 
 
 CO 1> CO ^ 00 
 
 
 
 00 1-1 CO CM Oi to 00 
 
 IN 
 
 1-H 
 
 IN 
 
 QOOCMi-JrHqOipi>;CD 
 
 
 U5 
 
 i-Ht6c0rHTi^CDi-5tO06cd 
 
 P^ 
 
 
 
 
 CM CM 1-1 1-1 00 
 
 < 
 
 ^ 
 
 Oi 00 Oi l> 
 
 T— 1 
 
 
 
 I5II • --IsSfl 
 
 
 
 
 
 
 ^ ^ ": g fl ^ fl ^— --3 
 
 
 
 •^ g.S 5-^ >>-S >>i^ ii . 
 5feO<10MOW^H 
 
 
 
 
 
DEVELOPMENT 271 
 
 destroyed by the early stunting resulting from insuffi- 
 cient food. The gains, the amount of food consumed, 
 and the gain in live weight based on each pound of 
 grain consumed is shown in the tables for the various 
 periods of the feeding experiment. (Tables on pages 
 269, 270.) It will be observed from the figures given 
 in these tables that the animal subjected to severe condi- 
 tions of feeding during its early life evidently had a 
 greater capacity for growth, and made better use of the 
 food consumed, than did the animal that received a 
 generous ration during the same period of its life. 
 There can be no question but that under certain con- 
 ditions a significant check to the development of an 
 animal may actually increase the rate of growth during 
 the later periods of its life. 
 
 256. Climate. — Small animals like mice and domestic 
 rabbits reared in artificially heated temperatures are 
 noticeably larger than normal size and have less hair on 
 the bodies. Cattle that are well fed and housed in warm 
 barns have much less hair than animals of similar breed- 
 ing that are required to live exposed to the rigors of severe 
 cold weather. 
 
 257. The age factor in animal-breeding. — Very large 
 numbers of farm animals are bred and produce offspring 
 while still immature. The use of young sires among 
 all classes of animals is general, but especially is their use 
 common in the breeding of hogs, sheep and cattle. 
 Various opinions exist among breeders as to the good or 
 evil effects which follow this practice. Some of the evil 
 results which it is claimed have followed the long-con- 
 tinued mating of immature animals are, a gradual decrease 
 in the size of the breed ; weakness of constitution ; loss 
 of prepotency in the transmission of valuable qualities; 
 
272 THE BREEDING OF ANIMALS 
 
 a retardation of the growth of the young parents and, in 
 some cases, a permanent dwarfing of the mother. 
 
 The supposed evil results following premature preg- 
 nancy must result either from variations produced in the 
 fundamental constitution of the germ-plasm or in changes 
 in the soma- or body-cells. Those breeders who contend 
 that long-continued breeding of immature animals results 
 in actually decreasing the size of the race or breed believe 
 that the real character of the breed has been changed, and 
 changed in such a way that the individuals of the breed 
 are no longer able to produce offspring which possess the 
 capacity to develop into animals of the recognized stand- 
 ard size of the breed. They would insist that the funda- 
 mental nature of the breed has been changed in such a 
 ■vYay as permanently to affect their hereditary character. 
 It is obvious that if this contention of breeders is correct, 
 it is contrary to our present ideas of the inheritance of 
 acquired characters. Biologists generally would first 
 insist on a more accurate demonstration of the alleged 
 fact that the size of the breed is actually diminished as a 
 result of early pregnancy and lactation. If it should 
 be found that this practice has apparently resulted in a 
 smaller breed, the biologist would undertake to explain 
 the observed fact on different grounds. 
 
 258. Premature breeding decreases size. — First, is it 
 true that premature breeding has ever resulted in decreas- 
 ing the size of the breed? It must be admitted that 
 experienced breeders are very often accurate observers. 
 Investigators who disregard the facts which have been 
 determined by practical breeders through a long period 
 of successful experience are neglecting a valuable source 
 of knowledge on many of the complex problems of heredity 
 and development. That breeders have observed that long- 
 
DEVELOPMENT 273 
 
 continued early breeding results in decreasing the size 
 of the breed is indicated from an investigation made by 
 J. M. Jones under the writer's direction in 1912. Spe- 
 cific questions were formulated and sent to a large r umber 
 of successful breeders in America and Great Britain. 
 From these replies it was determined that 216 breeders 
 had observed that early mating resulted in weakening 
 the breed, diminishing the fecundity, and decreasing the 
 size. That such results followed was denied by thirty-five 
 breeders. Of the total number replying, 158 believed 
 that the size was decreased but that fecundity was not 
 diminished. It is very clear from the statistics presented 
 and from the extended replies of the intelligent breeders 
 that under certain conditions the size of the animals 
 comprising the herd of a breeder who continually breeds 
 his animals prematurely is smaller than the size of ani- 
 mals in the herds of breeders who cause their animals to 
 mate at a more mature age. 
 
 259. Decreased size due to early breeding not in- 
 herited. — In recognizing the fact that premature breeding 
 does decrease the size of the breed under certain condi- 
 tions, it is not necessary for us to assume that the tend- 
 ency to decreased size in this case is inherited. Early 
 breeding can have no direct influence in changing the 
 fundamental constitution of the germ-plasm. It cannot, 
 therefore, change the general prepotency of the breed 
 in transmitting the recognized standard qualities of the 
 race. We must therefore look for an explanation outside 
 of the supposed influence on the hereditary powers of the 
 breed. The real effects from premature mating are to 
 be found in the development of the individuals as affected 
 by environment. The effects of gestation and lactation, 
 if observable at all, would be exhibited in the young par- 
 
274 THE BREEDING OF ANIMALS 
 
 ents or their offspring, or in permanent effects on the race 
 or breed. It might, in fact, influence all three. 
 
 260. Influence of early pregnancy on the mother. — 
 The chief harmful effect which follows the mating of 
 immature breeding animals is a retardation Or sudden 
 check to the growth of the young mother. Investigation 
 shows that the premature exercise of the breeding func- 
 tions in the young female acts in some instances as a 
 temporary inhibitor of growth. The author has for six 
 years compared the growth of immature mothers with the 
 normal growth curves of mothers mated when more 
 mature. In this investigation six Duroc Jersey sows were 
 divided into three groups. These groups of two sows 
 each were designated respectively as immature, half 
 mature and mature. The sows of the immature group 
 were bred at the beginning of puberty or at the first heat. 
 At this early period the young mother was very imma- 
 ture. The half mature sows were bred at about eighteen 
 months and the mature sows at about thirty months of 
 age. Careful records of the food consumed, the gain in 
 live weight, and increase in body measurements were made 
 of each animal in the experiment. Similar records were 
 made of the female offspring of the original sows for sev- 
 eral generations. The body measurements were taken 
 with a view to determining muscular and skeletal increase. 
 A large number of measurements was made, and these 
 clearly demonstrated the fact that the early exercise of 
 the breeding function in swine results in temporarily 
 checking the growth of the mother. The investigations 
 have progressed far enough at this time to measure also 
 the ultimate effect upon the mature mother. While 
 the observations have not yet included enough animals 
 to justify us in speaking with finality, yet it seems entirely 
 
DEVELOPMENT 
 
 275 
 
 safe to conclude that under certain conditions premature 
 breeding results in a permanent reduction in the normal 
 size of the mother. Young sows which have been bred 
 at the beginning of puberty and twice a year thereafter 
 until full maturity have in every case been smaller at 
 maturity than sows in the half mature and mature groups. 
 
 Retardation of Growth Due to Premature Breeding 
 
 OF Sows 
 
 Measurements taken at 42 months of age 
 
 
 Length of 
 Body 
 
 Heart 
 Girth 
 
 Height at 
 
 Withers 
 
 Depth of 
 Chest 
 
 
 Centimeters 
 
 Centimeters 
 
 Centimeters 
 
 Centimeters 
 
 Immatm-e^ . . . 
 
 106 
 
 125 
 
 65 
 
 41 
 
 (Factor 6) 
 Half Mature ^ . . 
 
 124 
 
 142 
 
 70 
 
 47 
 
 (Factor 3) 
 Mature^ .... 
 
 116 
 
 152 
 
 71 
 
 49 
 
 (Factor 8) 
 
 
 
 
 
 In the above table are recorded the more important 
 measurements of a typical representative of each of the 
 three groups. It will be observed that at forty-two months 
 of age the immature sow was materially smaller in length 
 of body, height at withers, depth of chest, and in heart 
 girth. At this age (three-and-one-half years) the young 
 sow had produced thirty-nine pigs in five litters, the half 
 mature sow sixteen pigs in two litters, and the mature 
 sow eight pigs in one litter. But one conclusion is possible 
 
 1 Has produced 5 litters and a total of 39 pigs. 
 
 2 Has produced 2 litters and a total of 16 pigs. 
 
 3 Has produced 1 litter and a total of 8 pigs. 
 
276 
 
 THE BREEDING OF ANIMALS 
 
 from these results, that early pregnancy and lactation 
 does retard the growth of the young mother. 
 
 Retardation of Growth Due to Premature 
 Breeding 
 
 Measurements taken at maturity — 66 months of age 
 
 
 Length of 
 
 Heabt 
 
 Weight at 
 
 Depth of 
 
 
 Body 
 
 Girth 
 
 Withers 
 
 Chest 
 
 
 Centimeters 
 
 Centimeters 
 
 Centimeters 
 
 Centimeters 
 
 Immature^ . . . 
 
 108 
 
 123 
 
 66 
 
 40 
 
 (Factor 6) 
 
 
 
 
 
 Half Mature 2 . . 
 
 120 
 
 127 
 
 67 
 
 44 
 
 (Factor 3) 
 
 
 
 
 
 Mature^ .... 
 
 118 
 
 143 
 
 71 
 
 48 
 
 (Factor 8) 
 
 
 
 
 
 In the above table the measurements of the same 
 animals at full maturity are shown. At the time these 
 measurements were taken the parents were about five-and- 
 one-half years of age. The sow that was mated at the be- 
 ginning of puberty and bred regularly thereafter, produc- 
 ing sixty-nine pigs in nine litters, was smaller at maturity 
 than either of the other groups which were mated at an 
 older age. This result has been secured in a number of 
 similar cases. In other words, the breeding of sows at a 
 young age not only results in a temporary check to their 
 development, but tends permanently to decrease the size. 
 This permanent decrease is not very marked and practi- 
 cally may not be of great importance. It is clear from the 
 
 1 Has produced 9 litters and a total of 69 pigs. 
 
 2 Has produced 6 litters and a total of 49 pigs. 
 
 3 Has produced 5 litters and a total of 32 pigs. 
 
DEVELOPMENT 277 
 
 records that one important practical result of early mating 
 is that by following this practice a much larger number 
 of young are produced during the lifetime of the parent. 
 In producing hogs commercially, this advantage might 
 easily overcome any disadvantage arising from a reduc- 
 tion in the size of the mother. 
 
 261. Gestation and lactation in relation to growth. — 
 The two most important phenomena associated with 
 reproduction which might have a measurable influence on 
 growth are gestation and lactation. The period of gesta- 
 tion in the mammalian domestic animals is the period dur- 
 ing which the embryo is developing in the uterus, from 
 the fertilization of the egg until the young animal is 
 sufficiently matured to carry on an independent existence 
 outside the body of the mother. During this period the 
 unborn animal increases rapidly in size, and within its 
 tissues the processes of cell division, absorption and 
 assimilation proceed with exceptional energy. The nutri- 
 tion for the growth of the foetus during this period is 
 supplied entirely by the pregnant mother. The foetus 
 itself has no means of nourishing its own tissues. It is 
 wholly dependent upon the mother. To all intents 
 and purposes the young animal in the uterus is an organic 
 part of the body of the mother. The foetus is an enormous 
 parasite nourished by the mother through the circulation. 
 
 It is a popular opinion among many breeders that 
 gestation is an exhaustive period for the mother, that 
 during this period the mother must not only provide for 
 her own physiological needs, but in addition must supply 
 the materials needed for the rapid development of the 
 foetus. It has been generally believed that because of 
 these facts the period of gestation is a severe strain on the 
 pregnant mother. If the mother herself has completed 
 
278 THE BREEDING OF ANIMALS 
 
 her growth or has approached maturity in her develop- 
 ment, the changes which take place in her organization 
 and which may be due to her pregnant condition will 
 obviously not affect her growth. On the other hand, if 
 the mother is young and growing rapidly, gestation 
 might act as a check to growth if the physiological pro- 
 cesses of the mother are necessarily and chiefly directed 
 toward the development of the foetus. The physiological 
 processes concerned in the nutrition of the foetus are 
 somewhat complex and the interrelations between the 
 mother and her unborn young not completely deter- 
 mined. The information available on the subject does 
 not specifically answer the question. We know that the 
 absorption of fats from the intestine proceeds at a more 
 rapid rate during pregnancy. Increased amounts of fat 
 in the liver cells also are associated with pregnancy. 
 
 There is a tendency to increase in body weight during 
 gestation. The maternal body increases in weight 
 independently of the increase in size of the foetus and 
 foetal membranes as shown by Gassner ^ and confirmed 
 by others. This increase in weight is common to the 
 mature pregnant mammalian mother and is not confined 
 to the young parent only. It is possible, therefore, that 
 this increase might be due to increased fat in the body 
 and not to any increase in the skeleton. If this were 
 found to be true, it would tend to confirm current opinion 
 as to the retarding influence of gestation on the growth. 
 
 262. The Missouri experiments. — At the Missouri 
 Experiment Station ^ careful measurements have been 
 made of a large number of immature pregnant sows and 
 
 1 Marshall, "Physiology of Reproduction," chap. XI. 
 - Mumford, Bulletins 131 and 141, Missouri Experiment 
 Station. 
 
DEVELOPMENT 279 
 
 of sows not pregnant for the purpose of answering, if 
 possible, the question whether gestation is a period of 
 such severe physiological strain on the young mother 
 that it stops normal growth. A large number of animals 
 have been under observation in this experiment and the 
 results are fairly uniform. Measurements included rec-* 
 ords of changes in body weight, heart girth, length of 
 body, height at withers, and other measurements. 
 
 The investigation is not complete, and further work 
 may modify the conclusions which seem fully warranted 
 at this time. The results so far justify the following 
 conclusions : 
 
 1. The exercise of the reproductive functions, con- 
 tinuously from the beginning of puberty to full maturity, 
 permanently decreases the normal adult size of the mother. 
 
 2. This permanent effect on the size of the mother 
 occurs even under a favorable environment. 
 
 3. The period of gestation is not a check to growth 
 when a full ration of nutritious food is supplied. The 
 rate of growth is not lessened during gestation. There 
 is some evidence that pregnancy is an actual stimulus to 
 growth. 
 
 4. The period of lactation is a very severe physiological 
 strain on the young mother, and during this period growth 
 is apparently inhibited. 
 
 5. After the end of lactation or when the young are 
 weaned, the rate of growth in the young mother is more 
 rapid than before pregnancy and more rapid than in 
 animals which have not been pregnant. 
 
CHAPTER XIV 
 THE PRACTICE OF BREEDING 
 
 If the modern breeds of domestic animals are com- 
 pared with the original unimproved forms, remarkable 
 differences will be observed. In many of the characters 
 which have come to be of inestimable value to man, the 
 modern animal is notably superior to the original unim- 
 proved forms. And in other characters, less substantial 
 and economically significant, modifications of great scien- 
 tific interest have resulted from systematic selection by 
 man. 
 
 263. Improvement in size. — For many purposes the 
 wild unimproved forms of the domestic animals are too 
 small to accomplish successfully the work required by 
 man. This demand for greater size and generally pro- 
 portional increase in strength has led breeders consciously 
 to select animals for size. The results of this selection 
 may be observed in the gigantic modern draft horse. 
 It is probable that all modern breeds of horses have 
 developed from the same original type. The wild form 
 was small in size, rough and somewhat angular in appear- 
 ance, with short mane and scanty tail. From this animal 
 we have through selection succeeded in producing the 
 large, powerful draft horse with smooth, broad contours 
 and heavy mane and tail. Contrasted with this type 
 we have well-recognized pony types weighing less than 
 400 pounds. Both types undoubtedly descend from the 
 
 280 
 
THE PRACTICE OF BREEDING 281 
 
 same prehistoric form. Each type breeds true. The 
 chief distinguishing character of size is firmly fixed in the 
 germ-plasm and we must come to the conclusion that 
 these radical differences have resulted from selection and 
 have become firmly established hereditary characters. 
 Similar differences in size among cattle, sheep and swine 
 supply additional evidence that size is a character which 
 may be radically changed through selection and that this 
 variation may become so firmly fixed that it may be re- 
 garded as an established characteristic of the breed. 
 
 264. Improvement in function. — The most remark- 
 able achievements in the improvement of the domestic 
 animals are undoubtedly improvements in the various 
 physiological functions of the animals useful to man. 
 Some of the most noteworthy of these are the milking 
 function in cattle, wool production in sheep, tendency 
 to fatten in meat animals, speed in horses and egg-laying 
 in the domestic fowls. A comparison of the productivity 
 of each of these types of animals with the unimproved 
 types gives ample evidence of the remarkable develop- 
 ment which has taken place through the agency of man's 
 selection. 
 
 265. The milking function. — The ability of mam- 
 malian animals to produce milk is closely correlated with 
 the reproductive functions. The mammary glands func- 
 tion primarily for the purpose of supplying a nutritious 
 and easily digested food for very young animals. Among 
 wild forms this function persists only for a comparatively 
 brief period and its continuance is determined by the 
 needs of the young mammal. Under domestication the 
 milking function in the domestic cow represents a re- 
 markable improvement. The wild cow probably sup- 
 plied milk to her offspring only four or five months. The 
 
282 THE BREEDING OF ANIMALS 
 
 amount of milk supplied by the wild cow is limited to a 
 few pounds daily. 
 
 The milking function in the domestic cow has become 
 through man's selection an hereditary character of the 
 greatest importance. While in the domestic cow the 
 milking function is still closely correlated with the repro- 
 ductive functions, it is nevertheless developed to such 
 an extent that it bears no very important relation to the 
 needs of the young offspring. Certain individual cows 
 have this function developed to such an extraordinary 
 degree that they produce milk continuously without inter- 
 ruption for many years and often regardless of whether the 
 cow becomes pregnant or not. (Plate XXVI.) 
 
 The Holstein Friesian cow, Duchess Skylark Ormsby 
 (Plate XXVII), produced 27,761 pounds of milk in one 
 year, containing 1205 pounds of fat. The Jersey cow, 
 Sophie 19th of Hood Farm (Plate XXVIII), has a record 
 of 17,557 pounds of milk containing 999 pounds of fat. 
 The Guernsey cow, Murne Cowan, is officially reported as 
 having produced 24,008 pounds of milk and 1098 pounds 
 of butter-fat in one year. Garclaugh May Mischief, an 
 Ayrshire cow, has a similar yearly record of 25,329 
 pounds of milk and 894 pounds of fat. 
 
 266. Improvement in wool production. — The first 
 importations of Spanish Merino sheep into the United 
 States were made about 1815. At that time the average 
 weight of fleece was three or four pounds. The weight 
 of fleeces of American Merinos increased gradually from 
 that time until 1885. Authentic records of single fleeces 
 weighing from thirty to forty pounds are now available. 
 The Oklahoma Agricultural College has reported that 
 the two-year-old Rambouillet ram Loraine owned by 
 that institution has produced a fleece weighing 46 pounds 
 
THE PRACTICE OF BREEDING 283 
 
 which is claimed to be the heaviest fleece ever taken from 
 a single sheep. The staple of this fleece was three and 
 one-fourth inches in length, which when straightened 
 measured five inches. It is interesting to note in this 
 case that the fiber was of unusual fineness, averaging 
 Yg^Q- of an inch in diameter. - According to Hunt,^ the 
 average weight of fleece of all sheep in the United States 
 in 1850 was 2.4 pounds a head. In 1900 the average 
 weight of fleece was 6.9 pounds a head. This remarkable 
 development in the improvement of the wool-producing 
 qualities of animals must be wholly credited to the skill 
 and enterprise of the American shepherd. 
 
 267. Improvement in tendency to lay on fat. — It is 
 more difficult to give accurate statistics showing the 
 improvement in meat-producing animals. At the begin- 
 ning of the eighteenth century, fat animals were not 
 placed on the market until they were four or five years of 
 age. Even as late as 1875, three- and four-year-old fat 
 animals were the most common types of cattle to be found 
 in the fat stock markets of America. By careful selec- 
 tion the tendency to lay on fat has been developed in 
 animals to such an extent that now it is common to find 
 young animals carrying fat equal to that shown by four- 
 and five-year-old bullocks of earlier years. This tend- 
 ency to lay on fat at an early age is transmitted through 
 heredity. The amount of food required to make one 
 pound of gain is much less in the younger animals and 
 the improvement in this respect, therefore, is of great 
 economic significance. It requires less food to-day to 
 produce the fat beef, pork and mutton sold in the markets 
 of the World than was the case before the improvement 
 of this tendency to early maturity. (Plates XXXI and 
 XXXII.) 
 
 ^ Hunt, " Cyclopedia of American Agriculture," vol. 3. 
 
284 THE BREEDING OF ANIMALS 
 
 268. Improvement in speed. — The ability to go fast 
 at the trot is a development of American horse-breeding 
 enterprise. The first trotting race was held at Boston 
 in 1815. The fastest time made in this race was a mile 
 in three minutes. As the result of interest in trotting 
 races and the invention of light horse-drawn vehicles, 
 the demand for speed at the trot resulted in great improve- 
 ment in this direction. The record time of trotting horses 
 decreased from year to year until at the present day (1916) 
 several horses have been developed that are able to trot 
 a mile in less than two minutes. The examples men- 
 tioned are all noteworthy as examples of man's power to 
 change fundamentally the form and function of the 
 domestic animal. These examples could be indefinitely 
 multiplied. 
 
 269. Selection. — All wild forms that have been do- 
 mesticated possess characters of economic value to man. 
 They were domesticated for that reason. These valuable 
 qualities have been, in many cases, greatly improved 
 through the agency of man. So great has been the im- 
 provement in many animal forms that the domesticated 
 animal is markedly different from his wild ancestors. 
 Many varieties, races or breeds exist and each of these 
 differs in important particulars not only from its wild 
 relatives but from all other varieties having similar ances- 
 tral history. 
 
 How have these valuable characteristics come into 
 existence? What natural laws have guided man in the 
 improvement of animals? Are the valuable character- 
 istics of animals due chiefly to inheritance or are they in 
 most part the result of improved conditions which sur- 
 round the domestic animals? Is it possible for us from 
 a study of the history of the achievements of animal- 
 
THE PRACTICE OF BREEDING 285 
 
 breeders to establish a guide to future practice in the 
 improvement of animals? Answers to these questions 
 not only have great value to practical breeders but have 
 profound biological significance. 
 
 270. Natural selection. — The theory of natural selec- 
 tion which has so long influenced and determined the 
 trend of zoological thought is an attempt to explain how 
 the qualities of animals in nature have come to be. 
 Through natural selection organic beings tend to adapt 
 themselves to their surroundings. The more nearly 
 the qualities of animals are favorable to a successful 
 existence under the conditions surrounding the individual, 
 the more certainly will the animal live and reproduce. 
 
 The insect that rests upon the branches of trees will 
 escape insectivorous birds more certainly if the color of 
 the body imitates that of the bark upon which it rests. 
 The color of the jungle animal blends so completely into 
 the general landscape that its presence is not detected 
 by its enemies. 
 
 The shore birds or waders in their pursuit of food in the 
 shallow waters of the shore have developed long legs. The 
 giraffe, feeding as it does upon the leaves on the branches 
 of trees, has found a long neck to be a desirable quality in 
 securing food. And in this case the longer the neck the 
 more certainly will the animal survive when food is scarce. 
 
 Darwin assumed that under conditions similar to those 
 mentioned, animals that vary slightly in the desired 
 direction would be preserved and would reproduce, while 
 those animals that varied away from the valuable quality 
 would perish. An animal might continue to develop 
 indefinitely in a given direction through continuous 
 variation. Darwin also recognized the existence of 
 discontinuous variation. 
 
286 THE BREEDING OF ANIMALS 
 
 The origin of the pecuHar characters which are valuable 
 in the domesticated animal is believed to have come 
 about through a similar process of selection but with this 
 difference : Man has introduced methodical selection by 
 which all animals are preserved, not only those suited 
 to their particular environment but also and chiefly those 
 which possess characteristics that are valuable to man. 
 Many complex and difficult questions have arisen in con- 
 nection with the improvement of the domesticated ani- 
 mals involving the most difficult problems of inheritance. 
 
 271. Methodical selection. — The selection practiced 
 by man is known as methodical selection. Animals are 
 selected because of their peculiar fitness for special pur- 
 poses. The powerful, heavy draft-horse is the result of 
 generations of careful selection and breeding in an effort 
 to produce an animal that can pull heavy loads. 
 
 In the same way but with a different standard of selec- 
 tion, the speed horse has developed an extraordinary 
 ability to run fast under the saddle or trot at a rapid pace 
 before the carriage. 
 
 Similarly, the beef animal, the dairy cow, the mutton 
 and wool sheep, the lard and bacon hog, the swift grey- 
 hound, the massive St. Bernard, the intelligent Scotch 
 collie and many other types useful to man have come 
 from methodical selection. 
 
 272. Importance of selection in animal-breeding. — 
 Careful study of the methods which have been practiced 
 by breeders of the domestic animals cannot fail to lead 
 to the inevitable conclusion that selection has been the 
 most important if not the chief principle followed in bring- 
 ing about the present highly developed forms among 
 animals. 
 
 Certainly not all the phenomena which are exhibited 
 
Plate XXIX, — Daughters of the same sire, illustrating great uniformity 
 in conformation and productive power resulting from the use of a prepotent 
 sire in the herd. These three cows have an average yearly record of 22,295 
 pounds of milk and 855 pounds of butter. Owner, University of Missouri, 
 
^/^JJ^S 
 
 
 Plate XXX. — Three generations showing impressive character of 
 original dam. Upper, Missouri Chief Josephine, yearly milk record 26,861 
 pounds. Middle, Missouri Josephine Sarcastic, daughter, yearly milk record 
 18,452 pounds. Lower, Carlotta Campus Girl, granddaughter, yearly milk 
 record 15,725 pounds as a two-year-old. Owner, Universitj' of Missouri. 
 
THE PRACTICE OF BREEDING 287 
 
 in the practices and results of animal-breeders can be 
 explained upon the basis of selection alone, but it is quite 
 certain that without selection little practical use could 
 be made of the known laws which govern the transmission 
 of characters. Man's chief agency in the improvement 
 of animals has not been a conscious effort to bring about 
 a series of variations or mutations of a certain kind, but 
 it has rather been in the direction of preserving such 
 valuable characteristics as have been already in existence 
 or have appeared through variation. These character- 
 istics have been intensified by judicious matings and 
 perpetuated as a result of the keen insight of the skillful 
 breeder. The successful breeder has ever in mind an 
 ideal. He is at all times alert to detect variations which 
 approach this ideal. 
 
 Darwin believed that most of the improvement wrought 
 in domestic animals was due to minute or continuous 
 variations from the less desirable to the more desirable. 
 This belief has been general among animal-breeders 
 themselves. Working upon this assumption, the work of 
 the breeder consisted merely in accurately observing the 
 variations which tended in the desired direction. 
 
 But continuous variation assumes a perfect series of 
 infinitesimal steps, each grading into the one higher or 
 lower. Such continuity exists in the growth of animals 
 from birth to maximum development. Continuous varia- 
 tion is also illustrated in the physical world by changes 
 in temperature. In the history of the improvement of 
 domestic animals there are many examples of marked 
 and sudden variations in the offspring which cannot 
 be continuous. Such variations have been called dis- 
 continuous variations or mutations. It is certain that 
 much of the improvement in the domestic animals has 
 
288 THE BREEDING OF ANIMALS 
 
 come from valuable mutations which have been recognized 
 by the alert breeder. 
 
 But whether the present valuable characteristics of 
 the domestic animals have come through continuous 
 variations or by sudden mutations or in any other way, 
 selection by man has been the one outstanding fact in 
 the development of the many valuable races and breeds 
 of animals. It is conceivable and very probable that 
 similar variations have been induced by similar causes 
 in all wild forms, but wild forms have remained relatively 
 stationery while the domestic races have been greatly 
 improved. 
 
 273. Aids to selection. — The breeder has consciously 
 or unconsciously brought to his aid numerous practices 
 which have greatly facilitated his efforts. The manu- 
 facturer who has invented a labor-saving device or a 
 complicated machine to perform certain work puts it to 
 the test by actually applying the machine to the work 
 in hand. Likewise the skillful breeder has found it greatly 
 to his advantage to test his animal creations by actual 
 performances. 
 
 The breeders of trotting horses have no means of deter- 
 mining how successful they are in producing speed except 
 by trial on the track and it is not only necessary to train 
 now and then a horse but every individual in the stud 
 must be tested to be certain that all possess the quality 
 of speed. 
 
 The highly successful breeders of meat animals, cattle, 
 sheep and swine, maintain their breeding animals in a 
 high state of condition. In some cases the meat animals 
 used for breeding purposes by noted breeders are kept 
 so fat as to interfere with the normal reproductive func- 
 tions. But even so, such a practice is essential to the 
 
THE PRACTICE OF BREEDING 289 
 
 skillful breeder because in no other way can he determine 
 whether or not his breeding animals themselves possess 
 the proper tendency to lay on fat which is an essential 
 characteristic of a well-improved meat animal. 
 
 A high condition of the breeding animals does not 
 in any sense give the beef animal a greater power to trans- 
 mit the tendency to lay on fat to the offspring, as some 
 breeders have believed, but it does give him a selective 
 device or measure by which he may always know whether 
 his breeding animals themselves possess the characters 
 which it is desired to transmit to the offspring. 
 
 The breeders of dairy cattle feed their cows to full 
 capacity and surround them with every favorable condi- 
 tion for the maximum production of milk. This practice 
 gives the breeder the only accurate measure of individual 
 performance and places in his hand a selective device by 
 means of which he can quickly eliminate from his herd 
 those animals that have not inherited the capacity for 
 high production. There is no other accurate measure- 
 ment which the breeder can employ that will certainly 
 register his progress in the improvement of his favorite 
 breed. 
 
 274. The real results of selection in the improvement 
 of the domestic animals. — The many improved breeds 
 of live-stock which are now possessed of qualities of great 
 economic value to man, have come to this possession 
 through artificial selection practiced by man. Are these 
 qualities which distinguish the improved breed from the 
 wild form a permanent possession of the race? Have 
 the selective processes applied by man resulted in so fixing 
 the desirable heritable characteristics that the breeder 
 may depend upon inheritance to repeat the characters 
 of the parents in the offspring? There are some indi- 
 u 
 
290 THE BREEDING OF ANIMALS 
 
 viduals in each breed that represent near perfection in 
 the development of characters. There are many others 
 that are more or less deficient in such characters while 
 other individuals are actually mediocre. Will the indi- 
 vidual with near perfect characters reproduce other 
 individuals of the same high quality ? Will the mediocre 
 sort beget like mediocrity ? In other words, are the quali- 
 ties which have resulted from artificial selection indelibly 
 impressed on the hereditary substance of the germ-plasm 
 in such a way as to be certainly transmitted to the off- 
 spring? Exact answers to these questions cannot be 
 given without full knowledge of all the conditions, but 
 recent investigations have thrown much light on these 
 important questions. 
 
 275. Selection within pure lines. — Selection as prac- 
 ticed by man has undoubtedly resulted in marked im- 
 provement of the domestic animals. This improvement 
 is apparently transmitted, or at least it is possible by 
 continued selection to reproduce desirable characteristics. 
 By continually selecting individual breeding animals 
 which show a tendency to vary in the direction desired, 
 it has been assumed that the race or breed would gradu- 
 ally move in the direction of selection. 
 
 At one period in the history of Shorthorn cattle, all 
 breeders were agreed that their improvement was mainly 
 to be accomplished in the direction of increased size. 
 Consequently the animals of greatest scale were selected 
 and mated with the apparent result that the average size 
 of the breed was increased. But actually what was 
 accomplished after many generations of selection? Was 
 a new breed created ? Had selection acted as a causa- 
 tive principle? The teachings of Darwin and his fol- 
 lowers has undoubtedly resulted in creating the impres- 
 
THE PRACTICE OF BREEDING 291 
 
 sion among many students that in this case a new breed 
 had actually been created with new characters resulting 
 from selection of continuous variations. That the results 
 obtained in this and similar examples may l:e explained 
 on other and more probable grounds has been clearly 
 demonstrated by Johannsen.^ This Danish botanist 
 working with garden beans found that the whole popula- 
 tion is made up of many races which he called " pure 
 lines." Selecting from populations composed of pure 
 lines, the breeder merely sorts out one of these races 
 and in time secures a pure line. This pure line or race 
 is not new. It has not resulted from gradual or continu- 
 ous variations but has simply been separated out from 
 a number of others. According to Johannsen, selec- 
 tion within a pure line during a number of generations 
 had no effect in improving the variety. The germ- 
 plasm of all individuals of a pure line tends to become 
 homogeneous. 
 
 The mating of individuals from a pure line having 
 in their respective germ-plasms identical factors will 
 result in producing identical offspring and hence any 
 amount of selection will prove futile. Such pure line 
 individuals are much more likely to be found among plants 
 than among animals. Plants that are self-fertilizing may 
 be expected to develop typical pure lines and selection 
 within such pure lines will be of no avail. Among the 
 higher animals similar results undoubtedly occur, but 
 the difficulties of securing a strictly pure line are very 
 much greater owing to the necessity of mating two dis- 
 tinct individuals whose ancestry, while similar, cannot 
 possibly from the very nature of the case, be exactly 
 identical. 
 1 Johannsen, "Elemente der exakten Erblichkeitslehre," 1909. 
 
292 THE BREEDING OF ANIMALS 
 
 276. Vilmorin's pure line wheat-breeding. — A good 
 example of the pure line theory among plants is to be 
 found in the very practical and meritorious work of 
 Louis de Vilmorin, who began the improvement of com- 
 mercial varieties of wheat in France about 1840. Vil- 
 morin carefully selected a single head of outstanding merit 
 and from this by in-breeding established a pure line or 
 variety which has bred true to the original ear or head. 
 The commercial seed offered by Vilmorin was always 
 descended from a single plant. Selection in this case 
 failed to bring about any improvement over the original 
 plant, as shown by the Hagadoorns.^ 
 
 "In 1911 Mr. Meunissier, the genetist of the firm of 
 Vilmorin, found the collection of original ears of the varie- 
 ties with which Louis de Vilmorin half a century back 
 began his living museum. Some of these wheats are 
 from the harvest of 1843, others date from 1850, or inter- 
 mediate dates. Mr. Meunissier chose three dozen ears 
 of varieties which are still in the collection, and which 
 have therefore been bred continuously as pure lines for 
 about fifty years. We compared these ears to ears of 
 the 1911 harvest, and photographed them side by side. 
 Some of these pairs of ears are here shown, each pair con- 
 sisting of the old ear, and its descendant, half a century 
 later. All these generations of selection have not changed 
 any one of the varieties one little bit. It can therefore 
 safely be concluded from this series of experiments, that 
 selection can have no effect in material pure for its 
 genetic factors. Genetic factors are constant." 
 
 277. Selection most useful when genetic factors are 
 not pure. — The pure line theorj^ explains why any 
 
 1 Mrs. C. and Dr. A. L. Hagadoorn, "Selection in Pure Lines," 
 American Breeder^s Magazine, 1913, p. 165. 
 
THE PRACTICE OF BREEDING 293 
 
 improvement among the best strains of animals is so 
 diflficult. Highly improved breeds or families among 
 the domestic animals have reached a degree of purity 
 wherein the germ-plasm represents an approach to homo- 
 geneity. When such a pure line has been established, 
 the old adage that " like begets like " becomes a really 
 working principle and a guide to practice. The novice 
 need not expect to accomplish great improvement in the 
 highly developed breeds of live-stock. The greatest 
 improvement will be made in breeds or strains of mixed 
 breeding, genetically speaking. 
 
 The improvement of animals of mixed character which 
 will result from the efforts of a breeder is probably to be 
 explained as a gradual separation of the desirable pure 
 lines and mating the individuals which possess these 
 characters. This results in time in the establishment of 
 a strain or breed which is prepotent in transmitting the 
 desired qualities when after many generations of pure 
 line breeding this strain has reached a point where the 
 germ-plasm of the breeding animals is pure in respect 
 to its genetic factors ; then any considerable improvement 
 will be no longer possible. 
 
 278. Pure line theory not opposed to improvement by 
 selection. — The practical breeder whose experience has 
 demonstrated clearly that improvement among the regis- 
 tered or '^ pure-bred " races of the domestic animals has 
 followed careful and persistent selection will hesitate 
 to accept the statement of Johannsen and his followers 
 that " selection within the pure line is without effect." 
 But the improved breeds of live-stock, however pure 
 in breeding, are not to be regarded as fulfilling the require- 
 ments of a " pure line " in the biological sense. The 
 breeds of live-stock are yet far from homogeneous in 
 
294 THE BREEDING OF ANIMALS 
 
 the sense that they have been selected to a point where 
 the germ-plasm of different individuals of the breed, is 
 identical in composition. The pure line of the biologist 
 is after all a purely imaginary conception. It is conceiv- 
 able that such a condition may be produced among self- 
 fertilizing plants, but among the higher animals it is 
 certainly true that no such germinal purity has yet been 
 attained. The practical animal-breeder may still con- 
 tinue to hold fast to selection as his chief means of im- 
 provement with the assurance that in all the higher do- 
 mestic animals we have not yet reached the ultimate 
 limits of improvement. The animal-breeder has not 
 yet produced a pure line, biologically speaking, and has 
 not, therefore, reached a point in his breeding when it 
 can be accurately said that selection is without effect.^ 
 
 279. Pedigree. — The pedigree of an animal is a record 
 of the ancestors. It is a valuable historical document. 
 If it includes the names of many animals of outstanding 
 quality, it is a good pedigree. If the ancestors were 
 mediocre individuals of no special merit, the pedigree 
 is inferior. The mere fact that an animal is recorded in 
 a recognized herd-book does not signify that such animal 
 has a good pedigree. The careful breeder must have a 
 thorough knowledge of the history of the breed and espe- 
 cially of the ancestors of the individual animal under 
 examination. 
 
 The immediate ancestors are most important. A 
 noted sire or dam appearing in the pedigree six or eight 
 generations back is of far less importance than one which 
 appears in the first, second or third generations. Many 
 breeding animals are sold on the strength of the fact 
 
 * Castle, "Pure Lines and Selection," Journal of Heredity, 
 1914, p. 93. 
 
HI A^ 1 
 
 & ■ *^ ''^^^ 
 
 fi^^^^lP^jd^^B^ .^^:4s«HJi 
 
 ^^I^Mp 
 
 
 ^^"^11 
 
 
 #r--' - -^ 
 
 1 
 
 .*?«S*«s#:-- 
 
 Pi 
 
 .;"-■ 
 
 n| 
 
 JM^iiT^iiffl 
 
 'iwitti^ JHH^nH 
 
 
THE PRACTICE OF BREEDING 295 
 
 that they are descended from some famous sire or dam 
 ten or even twenty generations back. If Galton's law 
 of ancestral heredity is a fair estimate of the potential 
 strength of a breeding animal, we should expect that 
 the individual animal would inherit one-half from his 
 two immediate parents, one-fourth from his four grand- 
 parents, and one-eighth from his eight great-grandparents. 
 From one great-grandparent, therefore, we should expect 
 the inheritance in the descendant to be represented by 
 the fraction g^. It is evident that a single ancestor six 
 or eight generations removed would contribute a very 
 small fraction of the sum total of qualities of the individual. 
 In the application of Galton's principle, it is necessary 
 to assume that all the ancestors are equally prepotent. 
 This assumption is contrary to the experience of breeders. 
 Certain individuals are known to be more prepotent 
 in certain characters, or, more properly speaking, certain 
 characters are dominant and others recessive. The 
 dominant characters will largely determine the character 
 of the offspring. It is conceivable that a dominant char- 
 acter which it is greatly desired to perpetuate in a strain 
 might reappear in the offspring through many genera- 
 tions. It might be argued that because of this fact a 
 study of the characters of an ancestor far removed hav- 
 ing this character would be valuable. To this it must 
 be said that if the character is dominant it will be clearly 
 apparent in the immediate ancestors. If it is not apparent 
 it may have been lost or overshadowed by the develop- 
 ment of other characters, and if so it is good evidence that 
 the real character of the strain is being determined by 
 nearer and stronger ancestors. Every modern biological 
 conception gives added weight to the principle that it is 
 the recent ancestors that should be most carefully in- 
 
296 THE BREEDING OF ANIMALS 
 
 vestigated by the practical breeder if he is to obtain any 
 valuable basis for estimating the breeding powers of an 
 individual. 
 
 280. Registered breeding animals. — In purchasing 
 a breeding animal, the breeder desires some guarantee 
 of purity of breeding. Every recognized breed, therefore, 
 maintains an association of breeders organized for the 
 purpose of safeguarding the purity of the breeding ani- 
 mals and advancing the general interests of the breed. 
 Each association maintains a record book in which every 
 animal recognized as a pure-bred animal of the breed is 
 recorded. Each association has its own rules governing 
 the registration of animals. In practically all breed 
 associations, the offspring of registered parents can be 
 recorded. There are few exceptions to this rule. In 
 some associations animals may be registered upon the 
 basis of their performance. The Standard Bred or 
 American Trotting Horse Registry Association will record 
 any animal that has made an authentic record of a 
 mile in two minutes and thirty seconds on an approved 
 track and under regulation rules. A few associations in 
 the past have permitted the registration of animals hav- 
 ing a certain number of top crosses to registered sires. 
 The history of all breed associations is similar. A few 
 animals of similar characters have attracted attention 
 because of their peculiar value for certain purposes. 
 These animals have been interbred and gradually a family 
 or strain developed which excels in certain valuable 
 characteristics. The admirers of this family or strain 
 have organized to preserve the strain. Experience has 
 shown that one of the first and most useful steps is to 
 record the individual breeding animals of outstanding 
 merit. The descendants of these animals constitute 
 
THE PRACTICE OF BREEDING 297 
 
 the breed, and ultimately only descendants of animals 
 recorded in the registry book are eligible to registration. 
 281. Registry associations. — The recognized registry 
 associations of the United States at present (1916) are 
 listed below : ^ 
 
 AMERICAN HORSE RECORD ASSOCIATIONS 
 
 Arabian Horse Club of America. 
 
 American Association of Importers and Breeders of Belgian 
 
 Draft Horses. 
 Cleveland Bay Society of America. 
 American Clydesdale Association. 
 French Coach Horse Society of America. 
 National French Draft Horse Association of America. 
 German, Hanoverian and Oldenburg Coach Horse Association 
 
 of America. 
 American Hackney Horse Society. 
 American Morgan Register Association. 
 Percheron Society of America. 
 The American Breeders' and Importers' Percheron Registry 
 
 Company. 
 American Saddle Horse Breeders' Association. 
 American Shetland Pony Club. 
 American Shire Horse Association. 
 American Suffolk Horse Association. 
 American Trotting Register Association. 
 The Jockey Club. 
 The Welsh Pony and Cob Society of America. 
 
 AMERICAN JACKS AND JENNET RECORD 
 ASSOCIATIONS 
 
 American B.reeders' Association of Jacks and Jennets. 
 Standard Jack and Jennet Registry of America. 
 
 AMERICAN CATTLE RECORD ASSOCIATIONS 
 
 American Aberdeen-Angus Breeders' Association. 
 
 Ayrshire Breeders' Association. 
 
 Brown Swiss Cattle Breeders' Association. 
 
 1 Data from United^ States Department of Agriculture. 
 
298 THE BREEDING OF ANIMALS 
 
 American Devon Cattle Club. 
 
 Dutch Belted Cattle Association of America. 
 
 American Galloway Breeders' Association. 
 
 American Guernsey Cattle Club. 
 
 American Hereford Cattle Breeders' Association. 
 
 Holstein-Friesian Association of America. 
 
 American Jersey Cattle Club. 
 
 American Kerry and Dexter Cattle Club. 
 
 Polled Durham Breeders' Association. 
 
 American Polled Hereford Breeders' Association. 
 
 Red Polled Cattle Club of America, Inc. 
 
 American Shorthorn Breeders' Association. 
 
 American Dairy Shorthorn Cattle Club. 
 
 AMERICAN SHEEP RECORD ASSOCIATIONS 
 
 American Cheviot Sheep Society. 
 
 American Cotswold Registry Association. 
 
 The Continental Dorset Club. 
 
 American Hampshire Sheep Association. 
 
 American Leicester Breeders' Association. 
 
 National Lincoln Sheep Breeders' Association. 
 
 American and Delaine Merino Record Association. 
 
 Dickinson Merino Sheep Record Company. 
 
 National Delaine Merino Sheep Breeders' Association of Wash- 
 ington County. 
 
 Standard Delaine Merino Sheep Breeders' Association. 
 
 American Rambouillet Sheep Breeders' Association. 
 
 International Von Homeyer Rambouillet Club. 
 
 Michigan Merino Sheep Breeders' Association. 
 
 Vermont, New York, and Ohio Merino Sheep Breeders' Asso- 
 ciation. 
 
 American Oxford Down Record Association. 
 
 American Romney Marsh Breeders' Association. 
 
 American Shropshire Registry Association. 
 
 American Southdown Breeders' Association. 
 
 American Tunis Sheep Breeders' Association. 
 
 GOATS 
 
 American Angora Goat Breeders' Association. 
 American Milch Goat Record Association. 
 
THE PRACTICE OF BREEDING 299 
 
 AMERICAN SWINE RECORD ASSOCIATIONS 
 
 American Berkshire Association. 
 
 American Large Black Pig Society. 
 
 Cheshire Swine Breeders' Association. 
 
 O. I. C. Swine Breeders' Association. 
 
 Chester White Record Association. 
 
 American Duroc Jersey Swine Breeders' Association. 
 
 National Duroc Jersey Record Association. 
 
 American Hampshire Swine Record Association. 
 
 American Poland China Record Company. 
 
 National Poland China Record Company. 
 
 Standard Poland China Record Association.^ 
 
 American Tamworth Swine Record Association. 
 
 American Yorkshire Club. 
 
 National Mule-foot Hog Association. 
 
 Mule-foot Hog Breeders' Association. 
 
 American Mule-foot Hog Record Company. 
 
 282. Community breeding. — The establishment and 
 maintenance of a recognized breed is a cooperative enter- 
 prise. No single individual can alone successfully estab- 
 lish and maintain a breed. Other things being equal, 
 the larger the number of breeders engaged in the improve- 
 ment of a given breed, the more certainly will the breed 
 be improved and established on a permanent foundation. 
 It is also true that it is distinctly to the advantage of a 
 breed to be owned by breeders living in the same region. 
 The interests of the breeders are greatly enhanced if 
 many workers in a restricted area are breeding the same 
 class of animals. This is particularly true in the case of 
 the person who maintains a small herd or flock. The 
 economic value of establishing for a community the repu- 
 tation of breeding a very large number of a certain breed 
 has been demonstrated in many localities in this and 
 other countries. Recognizing these advantages, educa- 
 tional organizations and breed associations have encour- 
 aged community breeding enterprises. In some localities 
 
300 THE BREEDING OF ANIMALS 
 
 this has taken the form of cooperation among three or 
 four small breeders in the purchase of a valuable bull. 
 In the United States many associations have been formed 
 among farmers for the purchase of a valuable stallion. 
 Even in the absence of conscious cooperation for improve- 
 ment, if a large number of the farmers in a given neigh- 
 borhood are like-minded in the selection of breeds and 
 all produce the same breeds, each particular animal will 
 actually be more valuable because prospective buyers 
 will be attracted by the opportunity for selection where 
 large numbers are available. 
 
 283. Importance of numbers. — The present high 
 quality of the highly improved and valuable breeds of the 
 domestic animals has been the result of long-continued 
 and rigid selection. The perpetuation of the improved 
 characters already obtained rests upon the opportunity 
 for continued selection of the same kind. The effective- 
 ness of selection will depend upon the number of individual 
 animals which are concerned in any given breeding proj- 
 ect. It follows, therefore, that the breeder who produces 
 large numbers has a decided advantage over the one 
 whose opportunity for selection has been confined to a 
 relatively small number of animals. A noted breeder of 
 dogs who was asked to give the secret of his success replied, 
 " I breed many and hang many." The breeder whose 
 operations are limited to a relatively small flock or herd 
 cannot expect to accomplish as much in the improvement 
 of any class of animals as the breeder handling much 
 larger numbers. 
 
 284. Selecting the best. — The improvement of ani- 
 mals has come chiefly through selection. In the actual 
 process of selection, men have followed various methods 
 with the ultimate purpose of obtaining finally a race or 
 
THE PRACTICE OF BREEDING. 301 
 
 breed of fixed characters, that is, characters which are 
 represented by definite determiners in the germ-plasm 
 in such a way that the individual animals of the breed 
 are able to transmit these desirable characters to their 
 offspring with a reasonable degree of certainty. Thus 
 many breeders have surrounded their animals or plants 
 with exceptionally favorable conditions and have selected 
 those which have developed the prized qualities most 
 perfectly under such conditions. This was the method 
 of Hallet in developing improved varieties of wheat. Un- 
 doubtedly many of the early breeders based this practice 
 upon a very deep-seated but mistaken belief in the in- 
 heritance of acquired characters. This method has been 
 very successful in a considerable number of cases, both 
 among plants and animals, but not because the environ- 
 mental factors involved had fundamentally changed the 
 real character of the germ substance. In all such cases 
 the improved environment acted merely as an efficient 
 selective device and indicated those individuals which 
 actually possessed the capacities valued by the breeder. 
 This method has often failed in accomplishing lasting 
 improvement, because the conditions surrounding the 
 breeding stock are not average conditions and the appar- 
 ent improvement may be wholly due to a better food 
 supply or more room and not due to fundamental differ- 
 ences in the germ. Another method of improvement 
 which involves selection of the best is to place the plant 
 or animal under ordinary or even unfavorable conditions 
 and select those individuals which appear best able to 
 develop the desired qualities under such conditions. 
 
 285. Selecting chance variations. — We know that 
 sudden and important variations often occur in the germ- 
 plasm. Some of these variations may be of such a char- 
 
302 THE BREEDING OF ANIMALS 
 
 acter as to have great economic value to man. Varia- 
 tions of this character are invariably transmitted, and the 
 wise and observant breeder may often make rapid prog- 
 ress by making such chance variation the basis of his 
 selections. This is the method of De Vries. In following 
 this method the breeder does not consciously undertake 
 to cause variation but rather to take advantage of those 
 which have resulted from natural causes. The breeder 
 of the domestic animals will often have difficulty in deter- 
 mining whether a given variation is due to environmental 
 causes or is due to fundamental changes in the germ-plasm. 
 The skillful breeder, however, will conclude with reason- 
 able assurance that when an individual animal exhibits 
 a rare and unusual aptitude in the development of a 
 certain character or characters, in a herd in which the 
 individuals are all maintained under identical conditions, 
 the rare development may be regarded as a germinal 
 variation. Such germinal variations may under certain 
 conditions become the foundation of a new strain. 
 
 286. The Burbank method. — If the selection of varia- 
 tions is the road to success in improvement, then why not 
 systematically attempt to cause variations and thus 
 increase the chances for discovering a desirable mutation ? 
 This is the plan followed by Burbank. By crossing a 
 great number of individuals, variations are secured, and 
 by a process of gradual elimination the outstanding vari- 
 ants are retained and reproduced. This plan does not 
 create any new forms, but depends on the well-known 
 tendency of unit characters to rearrange themselves in 
 new combinations which for all practical purposes may 
 really become a new creation. This method involves 
 the propagation of the improved individual by budding, 
 grafting or similar asexual method and cannot therefore 
 
THE PRACTICE OF BREEDING 303 
 
 be successfully applied in animal-breeding. This method, 
 like all the others described, is open to the objection that 
 it is after all based on mere chance. It is empirical and 
 unscientific. The proportion of failures to successes is 
 too great, and for these reasons it is a slow process of im- 
 provement. 
 
 287. The mendelian method. — The mendelian method 
 is based on the law of dominance and the segregation of 
 unit characters. The first step is to determine by the 
 behavior of the desired character in transmission whether 
 it is a dominant or a recessive character. If it is recessive, 
 then it is only necessary to combine two recessives, as 
 recessives are homozygous and always breed true. If 
 the desired character' proves to be a dominant, it is first 
 necessary to determine whether it is present in a heterozy- 
 gous or a homozygous condition. If it is homozygous, it 
 will breed true. If it is heterozygous, by in-breeding and 
 gradually eliminating the recessives it is possible greatly 
 to increase the number of dominants appearing and thus 
 practically establish a pure strain. This method is also 
 more successful in plant- than animal-breeding. The 
 animal characters which have come to be recognized as of 
 value to man are generally complex and do not behave 
 in transmission as unit characters. 
 
INDEX 
 
 f 
 
 Abortion, 120. 
 
 a cause of sterility, 120. 
 
 agglutination test for, 128. 
 
 contagious, 123. 
 * diagnosis of, 127. 
 
 treatment of, 124. 
 Acquired characters, 157-160, 162. 
 
 examples of, 162. 
 
 influenced by food supply, 162. 
 Acquired diseases, 180. 
 Age and fecundity, 96. 
 
 of poultry affects fertility, 96. 
 
 of ram influences fertility, 94. 
 
 of sheep influences fertility, 93. 
 
 of swine influences fertility, 91. 
 Age factor in animal-breeding, 271. 
 Agglutination test for contagious 
 
 abortion, 128. 
 Anaphase in cell division, 12. 
 Arkell, 187. 
 
 Artificial insemination methods, 44. 
 Asexual reproduction, 16. 
 Ash in ration, effect on foetus, 263. 
 At wood, 94. 
 
 Bachhuber, 50. 
 
 Barrenness, see also sterility, 119. 
 Bateson, 210. 
 Beard, 76. 
 
 Beinn Bhreagh flock, fertility of, 99. 
 Bell, 99. 
 Berberrich, 89. 
 Birth, number of young, 85. 
 Birthweight of lambs, 262. 
 Bitch, genital organs of, 32. 
 Blending inheritance, 135. 
 Blue-gray cattle, 247. 
 Border Leicester sheep, 87. 
 Boyd, 249. 
 
 Breeding prematurely decreases 
 size, 272. 
 
 Breeding season, 62. 
 
 dioestrum, 55. 
 
 metCBStrum, 55. 
 
 CEstrum, 55. 
 
 prooestrum, 54. 
 Brooks, 134. 
 
 Brown-Sequard experiments, 208. 
 Brull, 127. 
 Burbank method, 302. 
 
 Calcium in rations for pregnant 
 
 swine, 264. 
 Castle, 194-294. 
 Castration, 22. 
 
 influences secondary sexual char- 
 acters, 186. 
 Cattalo, 250. 
 Cell, 1. 
 
 contents, 4. 
 
 division, 8, 9, 10, 11. 
 
 germ, 2. 
 
 growth, 7. 
 
 structure, 4. 
 
 theory, the, 1. 
 
 the physiological unit, 3. 
 Cell division a cause of variation, 
 
 210. 
 Characters correlated with fertility, 
 102. 
 
 originate in germ-plasm, 195. 
 Chillingham cattle, 224. 
 Chromatin, 6. 
 Chromosomes, 12, 13, 135. 
 Cole, 50. 
 
 Color-blindness, 188. 
 Community breeding, 299. 
 Connaway, 128. 
 Contagious abortion, 123. 
 
 complement fixation test, 128. 
 
 diagnosis of, 127. 
 
 treatment of, 124. 
 
 305 
 
306 
 
 INDEX 
 
 Continuous and discontinuous 
 
 variations, 151. 
 Controlling sex, 189. 
 Cornevin, 229. 
 
 Corn ration, effect on foetus, 266. 
 Cow, reproductive organs of, 29. 
 Cows, exceptional fertility of, 107. 
 Cross, the first, an improvement, 
 
 247. 
 Cross-breeding, 243. 
 
 a cause of variation, 248. 
 
 advantages, 244. 
 
 effect on breeding powers, 244. 
 
 influences fertility, 105. 
 
 permanent results from, 243. 
 
 to increase fertility, 245. 
 
 to increase size, 246. 
 
 to restore constitution, 246. 
 Crossing and heredity, 247. 
 
 bison and cattle, 249. 
 
 species, 249. 
 
 Dalrymple, 125. 
 Darbyshire, 149. 
 Darwin, 52, 72, 90, 146, 198, 210, 
 
 221, 223, 225, 285. 
 Davenport, E., 100, 210. 
 Decreased size from early breeding 
 
 not transmitted, 273. 
 Development, 255. 
 De Vries, 152, 302. 
 Diagnosis of contagious abortion, 
 
 127. 
 Di-hybrids, 155. 
 Disease, 179. 
 
 acquired, 180. 
 
 congenital, 181. 
 
 predisposition, 181. 
 Duration of lactation, 81. 
 
 of oestrum, 63. 
 
 Early maturity, 283. 
 
 pregnancy, influence on mother, 
 274. 
 Eckles, 122. 
 Evvard, 263. 
 Ewart, 122, 168. 
 Exercise, effect on lactation, 83. 
 
 favors fertility. 111. 
 Experiments by Mendel, 131. 
 
 Factors affecting fertility, 100. 
 Fallopian tubes, 27. 
 
 obstruction of, 118. 
 Fatness, excessive, unfavorable to 
 
 fertility, 99. 
 Female reproductive organs, 24. 
 Fertility, 85. 
 
 characters correlated with, 102. 
 confinement unfavorable, 89. 
 correlated with size, 86. 
 domestication increases, 87. 
 duration of reproductive period 
 
 influences, 88. 
 exceptional in cattle, 107. 
 in horses, 106. 
 in poultry, 112. 
 in sheep, 110. 
 frequency of recurrence of oes- 
 trum, 88. 
 number of mammse as related to, 
 
 101. 
 nutrition, effect of, on, 98. 
 Poland China breed, 92. 
 relation of age to, 91-93. 
 relation of gestation to, 87-88. 
 Fertilization, 33. 
 
 changes in ovum resulting from, 
 
 36. 
 nature of, 34. 
 First cross an improvement, 247. 
 Flushing ewe, 99. 
 Foetal development and heredity, 
 
 261. 
 Foetus, size and vigor influenced by 
 
 ration, 266. 
 Food supply, excessive, causes 
 sterility, 99. 
 and body changes, 165. 
 influence of restricted, 165. 
 Free-martin, 129. 
 Function, improvement in, 281. 
 milking, 281. 
 
 Galton, 102, 295. 
 Gametic purity, 141. 
 Gentry, 234. 
 Germ-cells, 2, 12. 
 
 origin of, 40. 
 Germ-plasm, 161. 
 
 origin of new characters in, 206. 
 
INDEX 
 
 307 
 
 Gestation, 66. 
 
 causes of variation in period, 72. 
 
 period of, 69. 
 Geyelin, 97. 
 Goodale, 23, 187. 
 Goodnight, 249. 
 Graafian follicles, 25. 
 Grading, 244. 
 Growth, 256. 
 
 a cell function, 259. 
 
 by cell division, 7. 
 
 capacity for, 257. 
 
 development of foetus, 260. 
 
 effect of climate, 271. 
 
 factors influencing, 257. 
 
 impulse strongest in youth, 256, 
 260. 
 
 influence of age, 271. 
 
 influence of food supply, 257. 
 
 influenced by early pregnancy, 
 276. 
 
 relation of lactation to, 277. 
 
 retarded, permanency of, 268. 
 
 Hagadoorns, 292. 
 Hallett, 147, 301. 
 Hart, 64, 266. 
 Heape, 42, 54. 
 Heat or oestrum, 41. 
 
 duration, 63. 
 
 during pregnancy, 60. 
 
 effect of ration on, 64. 
 
 recurrence, 63. 
 Helme, 75. 
 Heredity, 131. 
 
 and development, 132. 
 
 and foetal development, 261. 
 
 and sex, 183. 
 
 and variation not antagonistic, 
 124. 
 
 definitions, 132. 
 
 kinds of, 134. 
 Hinny hybrid, 252. 
 Huish, 43. 
 Humphrey, 64, 266. 
 Huxley, 151. 
 Hybrids, 249. 
 
 cattle-bison, 249. 
 
 cattle-zebu, 253. 
 
 hinny, 252. 
 
 Hybrids — Continued 
 mule, 170-250. 
 sheep-goat, 254. 
 zebra-horse, 253. 
 
 Immunity, 181. 
 Improvement, 280. 
 
 in early maturity, 283. 
 
 in function, 281. 
 
 in milking function, 281. 
 
 in size, 280. 
 
 in speed, 284. 
 
 in tendency to lay on fat, 283. 
 
 in wool production, 282. 
 In-breeding, 217. 
 
 advantages claimed, 218. 
 
 bad results from, 219. 
 
 Berkshires, 234. 
 
 cattle, 223. 
 
 Darwin's researches, 231. 
 
 decreased fertility following, 220. 
 
 definition, 217. 
 
 dogs, 228. 
 
 fixing characters by, 240. 
 
 limits of, 238. 
 
 loss of vigor from, 220. 
 
 mice, 231. 
 
 pigs, 226, 234. 
 
 prepotency of in-bred animals, 241 . 
 
 researches of Ritzema Bos, 232. 
 
 results with different species, 242. 
 
 selection important, 238. 
 
 sheep, 227. 
 
 Wistar institute experiments, 233. 
 Incubation, fowls, 74. 
 Inheritance, 131. 
 
 alternative, 135. 
 
 blending, 135. 
 
 mendelian, 137. 
 
 mosaic, 136. 
 
 of disease, 179. 
 
 of polled character, 144. 
 Insemination, artificial, 42. 
 Intoxication of male parent, effect 
 
 on offspring, 49. 
 Iwanoff, 43. 
 
 Kehrer, 75. 
 Kempster, 97. 
 Kulbs, 89. 
 
308 
 
 INDEX 
 
 Lactation, 80. 
 
 duration, 81. 
 
 effect of exercise on, 83. 
 
 habit, 82. 
 
 heredity, 82. 
 
 influence of climate, 83. 
 
 mare mule that secretes milk, 83. 
 
 oestrum, 59. 
 
 relation of food supply to, 82. 
 
 unusual lactation, 83. 
 Lambs, birthweight of, 262. 
 Langer, 31. 
 Law, 68, 117, 124. 
 
 of ancestral heredity, 295. 
 
 of dominance, 139. 
 
 of segregation, 139. 
 Lead poisoning, effect on male germ- 
 cells, 50. 
 Lillie, 47. 
 Lock, 133. 
 
 Lord Morton mare, 167. 
 Lovejoy, 59, 236. 
 
 McCollum, 64, 266. 
 MacFadyean, 124. 
 Male reproductive organs, 19. 
 Males, milk secretion by, 28. 
 Mammae, number as related to fer- 
 tility, 101. 
 Mammary glands, 28, 81. 
 
 milk secretion by males, 28. 
 
 milk secretion in, 31. 
 
 structure of, 30. 
 Mare, genital organs, 26. 
 Marshall, 47, 53, 56, 96. 
 Maturation of ovum, 13. 
 Mendel, 136, 137, 138. 
 Mendelian method, 303. 
 Metaphase in cell division, 10. 
 Miles, 200. 
 Milk, 80. 
 
 analysis of milk from mare mule, 
 82. 
 
 secretion by males, 28. 
 
 secretion in mammary glands, 31. 
 Mironoff, 42. 
 Monohybrids, 155. 
 Monsees, 72. 
 Morgan, 184, 194. 
 Mule hybrid, 250. 
 
 Mule hybrid — Continued 
 
 and telegony, 170. 
 
 mare secreting milk, 84. 
 Mutation theory, 154. 
 Mutilations, 207. 
 
 Nabours, 253. 
 
 Nathusius, 72. 
 
 Nature and nurture, 159. 
 
 Nucleoli, 6. 
 
 Nucleus, 5. 
 
 Number of young at a birth, 85. 
 
 Nutrition influences fertility, 98. 
 
 (Estrum, 41, 55. 
 
 correlated with ovulation, 42. 
 
 duration of, 63. 
 
 effect of ration on, 64. 
 
 influenced by lactation, 59. 
 
 recurrence of, 63. 
 Origin of germ-cells, 46. 
 Ovaries, 24. 
 
 removal of, 23. 
 Oviparous animals, 18. 
 Ovum, 13. 
 
 fertilization of, 33. 
 
 Parturition, 75. 
 
 mal-presentation, 77. 
 
 normal, in domestic animals, 76, 
 
 78. 
 treatment for mal-presentations, 
 79. 
 Pearl, 96, 97, 103, 108. 
 Pearson, 103. 
 Pedigree, 294. 
 Penycuik experiments, 168. 
 Poultry, age influences fertility, 94. 
 Practice of breeding, 280. 
 Pregnancy, early influence on 
 mother, 274. 
 heat during, 60. 
 indications of, 66. 
 physical examination for, 68. 
 Pregnant swine, high calcium 
 
 rations for, 264. 
 Presence and absence hypothesis, 
 
 148. 
 Previous impregnation, influence of, 
 174. 
 
INDEX 
 
 309 
 
 Primary sexual characters, 19. 
 Prophase in cell division, 8. 
 Protein, effect of, on foetus, 266. 
 Protoplasm, 1, 2, 4. 
 Puberty, 56. 
 
 conditions influencing, 58. 
 Pure lines, 146, 291. 
 
 Vilmorin's wheat-breeding, 292. 
 
 Ram, age influences fertility, 94. 
 Recurrence of oestrum, 63. 
 Reduction, 37. 
 
 chromosomes, 37. 
 
 in the female, 40. 
 
 in the male, 41. 
 Registered breeding animals, 296. 
 Registry associations, 297. 
 Reproduction, 16, 183. 
 Reproductive organs, of the female, 
 24. 
 
 of the male, 19. 
 Retarded growth, caused by pre- 
 mature breeding, 274. 
 
 permanent effect of, 268. 
 Ritzema Bos, 232. 
 Rommel, 92. 
 Roux, 38, 39. 
 
 Secondary sexual characters, 19, 185. 
 Selecting the best, 300. 
 Selection, 284. 
 aids to, 288. 
 importance in animal-breeding, 
 
 286. 
 methodical, 286. 
 natural, 285. 
 Sex, 183. 
 
 effect of age on determination of, 
 
 189. 
 effect of nutrition on, 191. 
 influenced by maturity of ovum, 
 
 192. 
 not controlled by external condi- 
 tions, 194. 
 proportion influenced by season, 
 193. 
 Sex-linked characters, 188. 
 Sexual glands, transplantation of, 
 187. 
 reproduction, 17. 
 
 Sheep, fertility influenced by age, 
 
 93. 
 Size, decreased by premature breed- 
 ing, 272. 
 
 improvement in, 280. 
 
 of litter influenced by age, 91. 
 Somatoplasm, 161. 
 Sow, genital organs of, 30. 
 
 size of litter influenced by age, 
 91. 
 Spallanzani, 43. 
 Spaying, 23. 
 Spencer, 71, 133, 167. 
 Spermatogenesis, 41. 
 Spermatozoa, 14. 
 
 vitality within female generative 
 organs, 46. 
 Spermatozoon in fertilization, 37. 
 Sperm-cells, conditions influencing 
 vitality, 44. 
 
 weakened by too frequent breed- 
 ing, 45. 
 Steenbock, 64, 266. 
 Sterility, 113. 
 
 abortion, 120, 123. 
 
 causes, 114, 119. 
 
 closure of cervix, 117. 
 
 excessive food supply, 99. 
 
 fatty degeneration, 120. 
 
 in the female, 117. 
 
 in the male, 114. 
 
 obstruction in Fallopian tube, 
 118. 
 
 twin births (free-martin), 129. 
 Stockard, 50. 
 Superfoetation, 60. 
 
 examples of, 61. 
 
 Tanner, 104, 116. 
 Taylor, 126. 
 Telegony, 166. 
 
 possible appearance in mule 
 breeding, 170. 
 Telophase in cell division, 12. 
 Tessier, 70, 72. 
 Testicles, 20. 
 
 Theory of pure lines, 146. 
 Thomson, 133. 
 Thornton, 59. 
 Thury, 192. 
 
310 
 
 INDEX 
 
 Transmission of acquired charac- 
 ters, 157. 
 Transplanting sexual glands, 187. 
 Triplet calves, 108. 
 Trowbridge, P. F., 258, 268. 
 Twins, 101. 
 
 Union of egg and sperm, 36. 
 Unit characters, 141. 
 Use and disuse as causes of modi- 
 fications, 212. 
 Uterus, 28. 
 
 Variation, 195. 
 
 among cows, 203. 
 
 causes, 210. 
 
 continuous and discontinuous, 
 150, 151. 
 
 examples of, 200. 
 
 functional, 199. 
 
 germinal, 214. 
 
 infertility of animals, 200. 
 
 meristic, 198. 
 
 morphological, 196. 
 
 physiological, 197. 
 
 use and disuse, 212. 
 Verworn, 1. 
 
 Vilmorin's pure line wheat-breeding, 
 
 292. 
 Virchow, 2. 
 
 Viviparous animals, 18. 
 Von Guiata, 231. 
 Von Siebold, 192. 
 
 Waters, 257. 
 
 Weismann, 34, 38, 39, 167, 207, 
 210. 
 
 and Von Guiata's in-breeding 
 experiments, 231. 
 
 theory of reduction, 38. 
 Wentworth, 81, 101, 107. 
 Wheat-breeding, 147, 292. 
 Wheat ration, 263. 
 
 effect on fcetus, 263. 
 
 effect of mUk secretion, 267. 
 Wilsdorf, 230. 
 Wilson, 8, 33, 36, 38. 
 Wool production, improvement in, 
 
 282. 
 Wright, 74, 246. 
 
 Xenia, 176, 177. 
 
 Zebra hybrids, 168 
 
 Printed in the United States of America. 
 
THE following pages contain advertisements of a 
 few of the Macmillan books on kindred subjects 
 
The Breeds of Live-Stock 
 
 By Livestock Breeders. Revised and Arranged 
 By carl W. gay 
 
 Professor of Animal Husbandry in the 
 University of Pennsylvania 
 
 Rural Textbook Series. III., i2mo, $1.75 
 
 A more urgent demand, from a constantly increasing number of 
 consumers, for animal products must stimulate a greater exploita- 
 tion of pure-bred livestock as the source of the seed from which 
 market animals and their products are derived. The breeders who 
 will get the most out of the respective breeds with which they work, 
 will be those best informed as to the inherent possibilities of their 
 stock. Study of the origin, history, and development of the breeds 
 is, therefore, important. The most successful breeders are essen- 
 tially specialists and the most authoritative presentation of the his- 
 toric facts, points of merit, and economic importance of the different 
 breeds should be expected from those who have devoted themselves 
 most exclusively to these breeds. 
 
 Men who have been more or less eminently identified with the 
 respective breeds were chosen to prepare the breed material for the 
 Cyclopedia of American Agriculture. This matter has been revised, 
 brought up to date, and amplified to include types in their relation 
 to breeds, and the whole material has been edited, arranged, and 
 revised by Dr. Carl W. Gay, Professor of Animal Husbandry in the 
 School of Veterinary Medicine of the University of Pennsylvania. 
 The original illustrations are reproduced in half tones and the book 
 is oifered as the most complete and recent work on the types and 
 breeds of livestock. 
 
 THE MACMILLAN COMPANY 
 
 Publishers 64-66 Fifth Avenue New York 
 
The Principles and Practice of 
 Live-Stock Judging 
 
 By carl warren GAY 
 
 Professor of Animal Industry in the 
 University of Pennsylvania 
 
 Rural Textbook Series. Cloth, i2mo^ illustrated, $/.jo 
 
 This book has been prepared to meet the demand incident to the 
 progress made in livestock husbandry for a more comprehensive, 
 thorough, and systematic study of the judging of animals. The 
 effort has been made in its preparation to take the student and 
 stockman a step further than they have gone heretofore. Part I 
 introduces the principles upon which the practice of judging is 
 founded ; Part II applies to the practice of judging, definition and 
 procedure — the features of animal form to be considered, the means 
 of making observations and practice judging by the score card, 
 demonstrations, comparative and competitive judging. The bal- 
 ance of the work is devoted to special judging, one part being given 
 to each of the following : horses, cattle, sheep, swine, the judging 
 of breeding animals, and livestock shows. The volume is profusely 
 illustrated, typical representatives of the types and breeds being 
 shown in untouched photographs of animals to which championship 
 honors have been awarded. 
 
 THE MACMILLAN COMPANY 
 
 Publishers 64-66 Fifth Avenue New York 
 
Animal Husbandry for Schools 
 
 By MERRITT W. HARPER 
 
 Rural Textbook Series. Cloth, i2mo, illustrated, 4og pp., $1.40 
 
 With the increasing study of agricultural subjects in the schools 
 has come a demand for a book on Animal Husbandry suitable for 
 use by students of high school age. It is to meet such a need that 
 this book has been written, and in content, style, and arrangement 
 it is admirably adapted to the purpose. It belongs to the Rural 
 Textbook Series prepared under the editorial supervision of Profes- 
 sor L. H. Bailey of Cornell University. 
 
 In the five parts into which the book is divided the author treats 
 horses, cattle, sheep, swine, and poultry, and each is discussed with 
 reference to breeds, judging the animal, feeding, and care and man- 
 agement. There is also a chapter on the general principles of feed- 
 ing. Practical questions and numerous laboratory exercises sup- 
 plement the text and compel the student to think through each 
 subject as he proceeds. The book is extensively illustrated. 
 Designed for use as a textbook, it is also well suited for use as a 
 reference book in schools in which time limitations make it impossi- 
 ble to use it as a text. 
 
 THE MACMILLAN COMPANY 
 
 Publishers 64-66 Fifth Avenue New Yorl? 
 
The Feeding of Animals 
 
 By whitman HOWARD JORDAN 
 
 Director of the New York Agricultural Experiment Station 
 
 New edition, igib. Rural Textbook Series 
 
 This book has been revised partly to incorporate the more recent 
 knowledge concerning animal nutrition and partly to organize the 
 text into a more convenient form for student use. 
 
 As with the former edition, the text is divided into two parts; 
 Part I deals with the general principles of bio-chemistry that bear 
 upon animal nutrition. Part II discusses the practical side of feed- 
 ing animals with attention to such principles as relate specifically to 
 the nutrition of the various classes of farm animals. It is expected 
 that by this arrangement the volume will be useful for classroom 
 work with those students who have given little or no attention to 
 bio-chemistry as such, at the same time the interest is served of 
 those students who have given considerable attention to chemical 
 studies. The popular reader who is familiar with the general prin- 
 ciples of agricultural science should also find this treatise helpful in 
 the practice of animal husbandry. 
 
 THE MACMILLAN COMPANY 
 
 Publishers 64-66 Fifth Avenue New York