THE UNIVERSITY OF ILLINOIS LIBRARY NON CIRCULAT CHECK FOR UNBOUND CIRCULATE A Technical Study of the Growth of White Leghorn Chickens By H. H. MITCHELL, L. E. CARD, and T. S. HAMILTON UNIVERSITY OF ILLINOIS AGRICULTURAL EXPERIMENT STATION BULLETIN 367 CONTENTS PAGE INTRODUCTION 83 DESCRIPTION OF EXPERIMENT 84 EXPERIMENTAL RESULTS 85 GROWTH AS MEASURED BY BODY WEIGHT 85 Mathematical Description of Growth 86 Growth Curves and Equations 89 Mathematical Analysis of Growth Data 90 GROWTH IN SIZE AND FORM OF BODY 93 Percentage Increases 93 Effect of Sex 96 SURFACE AREA AT DIFFERENT AGES 96 Skin Areas of the Birds 96 Estimation of Skin Area by Mathematical Formula .... 97 Direct Determination of Surface Area 99 Prediction Formulas for Surface Area 101 Sex Differences 104 RELATIVE AND ABSOLUTE GROWTH OF VISCERA AND OF DIFFERENT PARTS OF CARCASS 105 Percentage Increases in Organ Weights 106 Sex Differences 109 Variability of Organ Weights 109 CHEMICAL COMPOSITION OF BIRDS AT DIFFERENT BODY WEIGHTS . . 109 Composition of Chemical Samples 109 Composition of the Birds 112 Percentage Distribution of Nutrients Among Chemical Samples. 113 Total Digestible Nutrients in Birds of Different Ages and Sex . 115 MATHEMATICAL ANALYSIS OF THE CHEMICAL DATA 116 MINIMUM NUTRITIVE REQUIREMENTS OF WHITE LEGHORN CHICKENS FOR GROWTH 124 TENTATIVE FEEDING STANDARDS FOR GROWING WHITE LEG- HORN AND WHITE PLYMOUTH ROCK CHICKENS ... 127 Protein Requirements 127 Calcium Requirements 128 Net Energy Requirements 129 Illustration of Use of Tentative Standards 134 Extension to Egg Production 135 SUMMARY 135 LITERATURE CITED . 139 Urbana, Illinois April, 1931 Publications in the Bulletin series report the results of investigations made or sponsored by the Experiment Station A Technical Study of the Growth of White Leghorn Chickens By H. H. MITCHELL, L. E. CARD, and T. S. HAMILTON* FORMULATION of feeding standards applying to dif- ferent classes of animals and to a variety of conditions is one of the most practical contributions of the science of nutrition to the feeding of farm animals. How greatly these standards have modified feeding practice cannot be told, but undoubtedly a knowl- edge of feeding standards and their limitations will aid the livestock man materially in the intelligent appreciation of his business, parti- cularly in the ability to cope successfully with changing conditions of feed supply and to avoid exploitation by manufacturers of commer- cial feeds, mineral mixtures, and other products for livestock. Feeding standards should promote maximal production with a minimum of overfeeding. They should include a factor of safety so that ordinary variation in the composition and nutritive value of feeds and in the functional capacities of animals will rarely result in underfeeding. . But obviously a definite factor of safety cannot be included in a feeding standard in any intelligent fashion until the actual minimum requirements of animals for the different nutrients have been determined. Hence feeding standards for farm animals must ultimately be based upon satisfactory determinations of mini- mum animal requirements. Feeding a farm animal in exact accord with its requirements for protein, or mineral matter, or even energy, may never be necessary or advisable, but when an animal is nonproducing at certain seasons of the year, or when protein concentrates become relatively high in price, it may become expedient to approximate these requirements, so that an exact knowledge of them becomes of practical value and importance. For these reasons, a study of the minimum nutritive requirements of chickens is justified from practical as well as scientific consider- ations. The fact that little information of this character has been obtained for chickens is but another reason for undertaking the present series of investigations. In Bulletin 278 of this Station 10 * a study of the growth of White Plymouth Rock chickens was reported. The study reported in this H. H. MITCHELL, Chief in Animal Nutrition; L. E. CARD, Chief in Poultry Husbandry; T. S. HAMILTON, Associate in Animal Nutrition. 83 84 BULLETIN No. 367 [April, bulletin is a similar investigation of Single Comb White Leghorn chickens. The purpose of both bulletins may be briefly described as follows : 1. To secure additional data on the normal rate of growth of chickens. The practical value of this information lies in the aid it will afford the animal husbandman in judging the success of his own feeding operations. 2. To determine how the visceral organs and the different anatom- ical parts of the carcass increase during growth, and how their weights, expressed as percentages of the body weight, vary with age. This information determines the value of the carcass of the chicken at any age as a source of food and, conversely, the amount of wastage in- curred in the preparation of birds of different ages for the table. It also possesses considerable biological interest in relation to the com- parative study of growth among different species of animals. 3. To determine the chemical composition of chickens of different ages and, by the application of mathematical methods for the descrip- tion of growth changes, the rates of deposition of the different food nutrients in the body at any age. The daily amounts of energy, of protein, and of mineral matter required for growth are determined primarily by the amounts added to the body each day, tho in satisfy- ing these requirements by food the composition of the food in net nutrients, rather than in total nutrients, must be considered. DESCRIPTION OF EXPERIMENT A flock of 1,000 Single Comb White Leghorn chicks, hatched about April 15, 1926, was available for this study. The chicks were range-reared at the University poultry farm on a ration consisting of yellow corn 80 parts, wheat middlings 10 parts, wheat bran 10 parts, ground limestone 5 parts, bone meal 5 parts, salt 1 part, and skim milk ad libitum. At the age of 10 weeks the cockerels and pullets were separated. The birds were weighed individually every two weeks, except for certain unavoidable irregularities in time in the latter part of the experiment. Samples of birds were removed for measurement and analysis according to weight. A sample of 10 newly hatched chicks (2 days old) was taken at the start of the experiment, and when the average weight of each flock reached approximately .5 pound, 1 pound, 1.5 pounds, 2 pounds, 3 pounds, and 4 pounds, samples of 10 cockerels and 10 pullets weighing very close to the average of their respective flocks were removed. A final sample of 10 cockerels was taken when the remaining cockerels averaged about 5 pounds in weight. All 1931} GROWTH OF WHITE LEGHORN CHICKENS 85 withdrawals of samples were made at the time of the biweekly weighings. The following measurements were made upon all birds removed for slaughter: 1. Depth from front end of keel bone to back 2. Depth from rear end of keel bone to back 3. Length from rump to shoulder 4. Circumference of trunk just back of wings 5. Length of shank 6. Length of middle toe 7. Length of drumstick 8. Length of keel bone 9. Breadth from hip to hip Upori completion of these measurements the birds were bled and dry-picked. The skins were removed, stretched, and outlined on paper, and their areas determined with a planimeter. The carcasses were then cut up and the weights of the following viscera and parts were taken: 1. Blood 13. Spleen 2. Feathers 14. Lungs 3. Head 15. Testicles (or ovaries and oviduct) 4. Neck 16. Pancreas 5. Shanks and feet 17. Gall-bladder 6. Skin 18. Gizzard 7. Legs above hock 19. Gullet, crop, and proventriculus 8. Wings 20. Intestines 9. Torso 21. Contents of alimentary canal 10. Heart 22. Total bones in dressed carcass 11. Liver 23. Total flesh (including fat) in 12. Kidneys dressed carcass For each group of 10 birds the following samples were composited for chemical analysis: 1. Feathers 2. Total bones in dressed carcass 3. Flesh and fat in dressed carcass, skin, and edible viscera, including liver, heart, and gizzard (minus lining) 4. Offal, including blood, head, shanks, and feet and all viscera except those included in Sample 3 All composite samples were analyzed for moisture, nitrogen, ether extract, ash, and calcium, and their content of gross energy was determined in the bomb calorimeter. The samples were preserved by refrigeration only. The percentage of dry substance in each sample was corrected, so far as possible, for moisture losses during dissecting, weighing, and grinding. EXPERIMENTAL RESULTS GROWTH AS MEASURED BY BODY WEIGHT The average body weights of the cockerels and pullets by two- week intervals up to 24 weeks of age and at irregular intervals up to 86 BULLETIN No. 367 [April, 40 weeks of age are given in Table 1. The table also contains the standard deviations and coefficients of variation of the body weights of the two groups of birds at each weighing. In this investigation the variation in body weight was less than 10 percent at hatching; at 6 weeks of age it increased to 16.6 percent TABLE 1. GROWTH AND VARIABILITY IN BODY WEIGHT OF WHITE LEGHORN CHICKENS Age Cockerels Pullets Number Body weight Number Body weight Average Stand. dev. Coef. of variation Average Stand, dev. Coef. of variation wks. 417 417 417 417 404 392 380 362 344 335 330 329 319 311 47 47 gms. 35.3 93 188 334 505 715 882 1 052 1 239 1 378 1 486 1 621' 1 716 1 883 2 334 2 309 2.90 10.74 29.2 55.5 75.1 118 126 329 157 202 111 203 182 201 8.2 11.6 15.5 16.6 14.9 16.5 14.3 31.3 12.7 14.7 7.4 12.5 10.6 10.6 362 362 362 362 346 335 324 317 307 304 299 293 269 231 205 203 gms. 35.0 90 177 302 443 605 740 844 988 1 113 1 218 1 327 1 380 1 694 1 694 1 726 3.48 11.01 28.3 59.9 68.9 87.3 89.6 107 136 131 143 141 137 9.9 12.3 16.0 19.9 15.6 14.4 12.1 12.6 13.7 11.8 11.7 10.6 9.9 2 4 6 8 10 12 14 16... 18 20 22 24 28 36 40 NOTE The sex of all chicks was recorded at 6 weeks of age. Weight data secured on chicks dying before reaching 6 weeks of age are therefore excluded from this table. for the cockerels and to 19.9 percent for the pullets, and then de- creased irregularly to about 10 percent at the later ages. The de- crease in variation of weight with increasing age was more regular and rapid for the pullets than for the cockerels. These changes of weight variability with age parallel in a general way those reported by Titus and Jull 17 * for Rhode Island Red chickens receiving skim milk in their mash and by Hanson and Heys 8 * for rats. These growth data may be profitably compared with those pub- lished by Buckner, Wilkins, and Kastle 3 * from the Kentucky Agri- cultural Experiment Station and by Card and Kirkpatrick from the Connecticut (Storrs) Station. 4 * This comparison is made graphi- cally in Fig. 1, from which it appears that the growth obtained with White Leghorn chickens in this investigation was not greatly different from that reported from the other two studies. At the younger ages growth was somewhat slower in the Illinois investigation, but at the later ages it was at least as rapid. Mathematical Description of Growth. The value of a mathemat- ical description of the growth of White Leghorn chickens in body 1931} GROWTH OF WHITE LEGHORN CHICKENS 87 2,500 Z.OOO o' ,0' > e O > oBuckncr,Wilkins,&K<9st!e Illinois do V o' o Buckner.Wilkins.&Kdsl Card&KirkpatricK Illinois ddbd le o ' o a ' 9*' 3 6 9 IZ 15 18 21 24 27 30 33 36 39 42 AGE IN WEEKS FIG. 1. GROWTH OF WHITE LEGHORN CHICKENS weight, as well as in the weights of chemical constituents, certainly justifies the labor involved. This description has been made purely as a step in the interpretation of the data secured in this study, with no pretense or implication that definite laws of growth for White Leghorn chickens are being defined in this way. The rationale of this application of mathematics is as follows: Animal growth, in any of its numerous aspects, is a dynamic phenomenon which may be supposed to proceed in a smooth and def- inite manner when the influence of disturbing factors is removed. 88 BULLETIN No. 367 [April, Growth is ordinarily studied in piecemeal fashion by attempting to determine the change with time of some animal measurement, such as body weight, or the weight of some definite organ, or the weight of protein in the body. If this is depicted graphically on coordinate paper, it will, under ideal conditions, move along a smooth curve, often a relatively simple one, the shape of which is defined by a simple mathematical function (equation) relating age (time) to the variable in question. More often, however, a simple mathematical equation will not describe the entire growth change, but only a fraction of it. Yet for the time range over which it describes the growth change, the mathematical equation is a complete, concise, and serviceable description of it. Quantitative observations of growth changes can be made only rarely under the ideal conditions just considered, this being partic- ularly true of the growth changes occurring in farm animals. The confinement of large numbers of these animals under uniform and favorable environmental conditions is quite impracticable. Hence disturbances in growth due to weather changes, feed changes, and digestive and other minor pathological affections of the animal occur, and they occasion irregularities in the measurements secured that bear no definite significance in relation to growth. When such meas- urements are plotted on coordinate paper, it is impossible to connect them by a curved line of any simple description, even over narrow ranges of time. The description by a mathematical equation of a series of actual observations upon the time changes occurring in growing animals is thus not a simple process. A choice must be made of the mathematical function that will be used, based upon the gross shape of the age-weight relationship, or upon the functions that have been used with most success in describing similar data. The con- stants in the mathematical function chosen must then be determined from the observational data by some method designed to secure a satisfactory fit. The mathematical equation thus obtained from the observed data expresses in the most satisfactory manner the time changes that would have been observed under the ideal conditions previously con- sidered. This equation may therefore be used as a substitute for the mass of data from which it was derived, in the same way, and for precisely the same reason, as an arithmetic mean (average) may be used to represent a mass of data clustering about a point rather than a curve. The advantages of thus reducing a series of variable and discon- nected observations relating to growth to a continuous mathematical 1931] GROWTH OF WHITE LEGHORN CHICKENS 89 function are important. From such a function the most probable value of the growth measurement may be computed for any instant of time, regardless of the time intervals at which measurements were actually taken. Also the estimation of the value of the measurement at any given time is not unduly affected by any disturbing conditions that may have produced irregularities in growth at or near that time, since the estimation is based upon all the data obtained rather than on a few selected values. From the equations describing the growth data, the rate of change in the measurement at any instant of time, as well as the change in the measurement during any definite interval of time, may also be readily computed a most important advantage of this mathematical method of analysis. The original mass of data cannot, by any other method, be made to yield satisfactory informa- tion of this nature. Hence for the most productive study of growth the application of mathematical methods is essential. Growth Curves and Equations. Many attempts have been made to describe the growth of animals and of plants by means of math- ematical equations relating the measurement under consideration with the age of the animal, taken either from birth or from conception. Such equations may be purely empirical in character, the investigator being content to use any type of equation that will fit the data satis- factorily and yet not contain an inordinate number of constants, the values of which are to be determined from the data. On the other hand, other investigators have selected certain types of equations on the basis of definite assumptions concerning the laws of growth. In these equations the constants possess a certain biological significance and may be evaluated approximately by mere inspection of the data, or by simple graphical methods. The latter type of equation unquestionably would possess a marked preference over the former if the laws of change that they express were established for growth, or were so plausible as to be generally acceptable. But such is not the case ; their value in express- ing growth changes must after all rest upon an empirical basis, i.e., upon the success with which they describe the change, with time, of actual growth measurements. The two equations of this character that have been used the most in this country are the Robertson equa- tion, 15 * in which growth changes are likened to the progress of an autocatalytic monomolecular chemical reaction, and the equation of Brody, 2 * which assumes that after a certain stage of growth is reached, successive increments in growth bear a definite and constant relation- ship to each other. Neither equation (the latter admittedly) has been found satisfactory in describing growth from its beginning to its com- 90 BULLETIN No. 367 [April, pletion, and in using them in a rational way to describe certain seg- ments of the growth curve one must postulate the existence of cycles of growth. In defining these cycles there is always the danger of ascribing to fortuitous depressions or accelerations of growth, occa- sioned by changes in environmental conditions, a biological signifi- cance that they do not possess. After all, the advantages of these so- called rational growth equations seem to be that they have been used with some degree of success in describing animal growth, that they possess only three constants to be evaluated, and that these constants possess a more or less definite biological significance. In a recent discussion of the kinetics of growth, Gray 7 * says: "... the comparison of metazoon growth with the behavior of comparatively simple chemical reactions meets with three main difficulties. Firstly, a series of observations which approximate to a sigmoid curve can only be expressed in the form of a specific differential equation when the accuracy of the observations reaches a very high level. Until such data are available it is impossible to determine how far they can only be expressed by the highly specific curves applicable to chemical systems. Secondly, there is no direct method of determining the active mass of the growing substance or of the other factors involved in the reaction : these may be proportional to the weight of the organism although no definite proof exists. Thirdly, the growing system is known to be statistically heterogeneous, and in the absence of reliable evidence to the contrary, it is intrinsically improbable that the system will behave like a system whose heterogeneity is constant . . . "An equation representing the size of a population of cells or of an organism in terms of age, yields, on differentiation, a quantitative but empirical representation of the factors controlling the rate of growth, but since more than one equation can always represent a typical growth curve within the limits of probable error, a selection of one particular equation rests solely on the intrinsic probability of its differential form. The degree of probability can only be established by direct experiment." Concerning Robertson's method of using his exponential equation successively in describing successive "cycles of growth," Gray says that by selecting suitable constants and "by using an appropriate number of superimposed curves there can be no doubt that an equa- tion of this type can be shown to express the facts. Unless, however, there are definite experimental reasons for adopting this procedure, the equation has no real meaning unless its advocates can prove that no other equation will fit the facts." Regarding Brody's exponential equations Gray says: ". . . it is sufficient to point out that any curve can be expressed as a series of straight lines or exponential curves if suitable limits are selected. Unless, therefore, there is good independent evidence that the whole growth cycle is divisible into a finite number of successive and different processes, the process of subdivision of the growth curve is purely arbitrary." Mathematical Analysis of Growth Data. In the present investi- gation the choice lay between the application of two so-called rational 1931] GROWTH OF WHITE LEGHORN CHICKENS 91 growth equations, in the manner of Titus and Jull, 17 * or the use of one frankly empirical equation. The growth data relating to body weight are fairly numerous, but the chemical data, which are to be inter- preted by this means also, consist of several series of only seven or eight observations each. To fit two equations containing three con- stants each to such small series of data was not considered advisable. Therefore, with some feeling of regret, a purely empirical polynomial equation of the fourth degree of the type W = a + bt + ct 2 + dt 3 + (1) was used thruout. In all cases the constants of this polynomial were determined by the method of least squares. 1 For the age-body-weight relation, the following equations were obtained for cockerels and pullets, respectively: W = -4 + 43. 70f + 4.072/ 2 - .1611/ 3 + .001731/ 4 (2) W = 21 + 33.9S/ + 3.149/ 2 - .1083/ 3 + .0008637/ 4 (3) Here W is the body weight in grams and / the age in weeks from TABLE 2. GROWTH OF WHITE LEGHORN CHICKENS, OBSERVED AND ESTIMATED (All weights in grams) Cock erels body w eight Pul ets body wei ght Observed Calculated 1 Difference Observed Calculated 1 Difference wks. 35 35 21 14 2 93 99 + 6 90 101 +11 4 188 2'6 +38 177 201 +24 6 334 372 +38 302 316 +14 8 ... 505 558 +53 443 443 10 715 706 9 605 576 -29 12 882 865 -17 740 713 27 14 1 052 1 031 21 844 850 + 6 16 1 239 1 192 -47 988 984 - 4 18 1 378 1 344 34 1 113 1 112 1 20 1 486 1 487 + 1 1 218 1 232 +14 22 1 621 1 618 - 3 1 327 1 342 +15 24 1 716 1 738 +22 1 380 1 440 +60 26 1 844 1 525 28 . . 1 883 1 963 +80 1 694 1 595 -99 30 2 024 1 651 32 2 100 1 691 34 2 170 1 715 36 2 334 2 237 -97 1 694 1 725 +31 38 2 305 1 719 40 2 309 2 379 +70 1 726 1 700 -26 'Using the equation: W J Using the equation: W -4 + 43.70/ + 4.072/* 21 + 33.9S/ +3.149/1 _ - .1611/' + .001731/ 4 . .1083/' + .Q008637/ 4 . 'Acknowledgment is made to Miss Florence L. White, Research Assistant in the Bureau of Business Research of the University of Illinois, for the mathematical work of fitting this equation to the growth data reported in this bulletin. 92 BULLETIN No. 367 [April, 2,500 2.000 at ? 1,500 i- X UJ < ^^ o C OCK E.REL .5 ^ x*" ^ X / 7^ y, / * 1,000 00 500 o ) 7 j / / W= -4+4 3.70t +4.07, ?t l -.l6llt s +jOOI73lt S ^> 0369 12 15 18 21 24 27 30 33 36 39 42 AGE IN WEEKS E.OOO < 1.500 o GHT o o O I 500 oo X PULLETS 3 6 9 12 15 18 21 24 27 30 33 36 39 42 AGE IN WEEKS FIG. 2. GROWTH OF WHITE LEGHORN CHICKENS, OBSERVED AND ESTIMATED hatching. The fit of these equations to the two sets of growth data is shown numerically in Table 2 and graphically in Fig. 2. From hatching to about 20 weeks of age the average body weights of both cockerels and pullets appear to follow an S-shaped curve, with a point of inflection at an age of 8 or 10 weeks that is not adequately reflected in the polynomial equation. A somewhat better fit for the data of this range has been obtained by the use of Robertson's growth equation. 15 * The differentiation of Equations 2 and 3 will permit the calcula- fdW\ tion of the rates of gain I -j- I at any age. Expressed as the rate ot \ at / 1931} GROWTH OF WHITE LEGHORN CHICKENS 93 gain in grams per day, these differential equations are For the cockerels: For the pullets: dW dt dW dt = 6.2 + 1.163/ - .0690/ 2 + .000989/ 3 (4) = 4.8 + .900/ - .0464/ 2 + .000493/ 3 (5) From these equations it may be calculated that at the ages (ob- tained from Equations 2 and 3) at which the chickens attained aver- age weights of .5, 1, 1.5, 2, 3, 4, and 5 pounds, the rates of gain in- grains per day were as given in Table 3. TABLE 3. ESTIMATED RATES OF GAIN IN BODY WEIGHT BY WHITE LEGHORN CHICKENS AT DIFFERENT BODY WEIGHTS Body weight Cockerels Pullets Age Daily gain Age Daily gain Ibs. .5 wks. 4.0 6.9 9.6 12.5 18.2 25.4 36.9 gms. 9.9 11.2 11.9 11.8 10.5 7.4 4.8 wks. 4.4 8.2 11.5 14.8 22.4 gms. 7.9 9.4 9.8 9.6 7.2 1 1.5 2 3 4 5 GROWTH IN SIZE AND FORM OF BODY The average linear and circumference measurements of the birds, taken before slaughter, are summarized in Tables 4 and 5, each aver- age representing 10 individual measurements. 1 The individual meas- urements for each weight group were generally very uniform. The coefficients of variation have been calculated for the cockerel measure- ments and will be found in Table 6. Of the 61 coefficients there recorded, 96.7 percent were equal to or less than 6, 91.8 percent were equal to or less than 5, 80.3 percent were equal to or less than 4, 50.8 percent were equal to or less than 3, and 14.8 percent were equal to or less than 2. These birds were more uniform in size than in weight (Table 1). Percentage Increases. Change in size of birds with increasing age, as revealed by these linear and circumference measurements, may be studied to better advantage by expressing each average value as a percentage of the corresponding value at the .5-pound weight. The percentages for cockerels are given in Table 7, and those for pullets in Table 8. These tables include also similar percentages for 'No measurements of this nature were taken on the day-old chicks. 94 BULLETIN No. 367 [April, body surface as determined from skin area. Expressed in this man- ner, it appears that the birds increased in size in such a way that their shape or conformation, exclusive of feathering, did not change greatly. This seems to be a proper interpretation of the fact that at any weight, the measurements taken, except the length of the middle toe, were approximately the same percentages of the corresponding measure- ments of the lightest birds measured. The body weight and the surface area of the bi"ds, however, increased much more rapidly than TABLE 4. AVERAGE BODY MEASUREMENTS OF WHITE LEGHORN COCKERELS AT DIFFERENT WEIGHTS (Each figure is an average of 10 birds; all measurements in centimeters) Approximate slaughter weight. . . .5 Ib. 1 Ib. 1.5 Ib. 2 Ibs. 3 Ibs. 4 Ibs. 5 Ibs. Age in days 44 58 72 86 107 156 219 218 477 678 875 1 317 1 719 2 136 Depth at front end of keel Depth at rear end of keel . . 5.7 5 5 7.4 6 8 8.4 7 8 10.9 9 5 12.2 10 12.6 10 9 Breadth at hips 4.0 5.2 5.9 6 3 7 8 8 5 9 4 5 6 7 5 8 6 10 7 11 1 12 3 13 3 Length of drumstick 7.5 10 11.6 13 3 15 5 16 6 17 1 Length of shank 5.7 7.7 9.0 10.1 12.0 12.5 12..9 4 5 5 7 6 3 7 7 8 7 8 7 9 Distance from rump to shoulder. . Midcircumference 9.6 14.7 12.7 20.1 14.5 22.9 16.0 24.9 19.0 28.5 20.4 31.7 21.3 34.0 TABLE 5. AVERAGE BODY MEASUREMENTS OF WHITE LEGHORN PULLETS AT DIFFERENT WEIGHTS (Each figure is an average of 10 birds; all measurements in centimeters) Approximate slaughter weight .51b. 1 Ib. 1.5 Ibs. 2 Ibs. 3 Ibs. 4 Ibs. Age in days 44 58 72 100 159 233 223 468 669 890 1 367 1 716 Depth at front end of keel . . . Depth at rear end of keel .... Breadth at hips 5.7 5.3 4.0 7.4 6.7 5 3 8.5 7.8 6.1 9.7 8.6 6.7 10.8 9.6 7.9 11.3 11.2 8.7 5 4 7 7 8 5 9 5 11 6 11.8 Length of drumstick 7 4 10 2 11.7 13.3 14.1 14.4 5 6 7 7 8 9 10 10 3 10.5 4 4 5 6 6 4 6.5 6 8 6.7 Distance from rump to shoul- der. . 9 7 13.0 14.9 16.5 18.6 19.3 Midcircumference 15.2 20.2 23.1 25.8 29.6 30.6 TABLE 6. COEFFICIENTS OF VARIATION OF BODY MEASUREMENTS OF WHITE LEGHORN COCKERELS AT DIFFERENT WEIGHTS Approximate slaughter weight. . . .5 Ib. 1 Ib. 1.5 Ibs. 2 Ibs. 3 Ibs. 4 Ibs. 5 Ibs. Depth at front end of keel 2.3 3.8 2.4 2.4 3.3 2.0 Depth at rear end of keel ....:.. Breadth at hips 3.6 2.4 5.1 3.0 3.4 2.1 2.2 3.2 2.0 7.1 1.9 3.2 3.4 Length of keel 11 2 4 4.6 3.4 5.8 4.4 4.7 4 3 1 8 3 1 5 8 2 9 2.7 3.6 3 2 3 3.0 2.6 3.7 3.0 4.6 Length of middle toe 5.0 3.4 3.9 4.6 2.6 2.5 3.6 Length from rump to shoulder. . . Midcircumference 3.1 2.5 2.5 2.4 1.7 2.1 2.7 3.1 2.4 2.0 3.1 2.0 1.5 1.7 1931} GROWTH OF WHITE LEGHORN CHICKENS 95 the linear measurements, the body weight increasing more rapidly than the body surface. For surfaces of similar shape the areas will vary with the squares of any linear measurement of the geometrical figure inclosing the surface. The skin areas of the birds, particularly of the pullets, it is TABLE 7. RELATIVE INCREASE IN BODY WEIGHT, BOD\ SURFACE, AND BODY MEASUREMENTS OF WHITE LEGHORN COCKERELS E URING GROWTH (Expressed in percentage) Approximate slaughter weight. . . .5 Ib. lib. 1.5 Ibs. 2 Ibs. 3 Ibs. 4 Ibs. 5 Ibs. Body weight 100 219 311 401 604 789 980 Body surface 100 193 286 335 465 522 574 Body measurements Depth at front end of keel .... Depth at rear end of keel Breadth at hips 100 100 100 130 124 130 147 142 147 157 191 173 195 214 182 212 221 198 235 Length of keel 100 134 154 191 198 220 237 Length of drumstick 100 133 155 177 207 221 228 Length of shank 100 135 158 177 210 219 226 100 127 140 156 173 173 176 Distance from rump to shoulder Midcircumference 100 100 132 137 151 156 167 169 198 194 212 216 222 231 TABLE 8. RELATIVE INCREASE IN BODY WEIGHT, BODY SURFACE, AND BODY MEASUREMENTS OF WHITE LEGHORN PULLETS DURING GROWTH (Expressed in percentage) Approximate slaughter weight . .5 Ib. 1 Ib. 1.5 Ibs. 2 Ibs. 3 Ibs 4 Ibs Body weight . . 100 210 300 399 613 770 Body surface 100 185 251 313 399 415 Body measurements Depth at front end of keel 100 130 149 170 189 198 Depth at rear end of keel 100 126 147 162 181 211 Breadth at hips 100 132 152 167 197 217 Length of keel 100 143 157 176 215 219 Length of drumstick 100 138 158 180 191 195 Length of shank . . 100 137 159 179 184 187 Length of middle toe 100 127 145 148 155 152 Distance from rump to shoulder. . Midcircumference 100 100 134 133 154 152 170 170 192 195 199 201 interesting to note, varied approximately in accordance with the square of the average linear measurement, exclusive of the length of the middle toe. For example, the linear measurements of the 1-pound pullets, with the exception noted, averaged 1.34 times the correspond- ing measurements of the .5-pound pullets. The square of 1.34 is 1.80, which approximates closely to 1.85, the ratio of the surface area of the 1-pound pullets to the surface area of the .5-pound pullets. The square of the average ratio of the eight linear measurements of the 1.5-pound pullets to those of the .5-pound pullets is 2.37, which is not far removed from the corresponding surface ratio of 2.51. For the 2-pound pullets, the squared ratio relating to the linear measurements is 2.96 as compared with 3.13, and for the 3- and 4-pound pullets, the comparable ratios are, respectively, 3.72 and 3.99, and 4.12 and 4.15. 96 BULLETIN No. 367 [April, The agreement is not so close for the cockerels. For the successive groups of cockerels starting with the 1 -pound birds, the ratios are as follows: 1.74 and 1.93, 2.28 and 2.86, 2.99 and 3.35, 3.84 and 4.65, 4.49 and 5.22, and 5.06 and 5.74. Effect of Sex. The effect of sex upon body size is most effectively shown by the calculations given in Table 9. In this table the nine TABLE 9. AVERAGE BODY MEASUREMENTS OF WHITE LEGHORN PULLETS AT DIF- FERENT WEIGHTS, EXPRESSED AS PERCENTAGES OF CORRESPONDING MEASUREMENTS OF COCKERELS OF LIKE WEIGHT Approximate slaughter weight .5 Ib. 1 Ib. 1.5 Ibs. 2 Ibs. 3 Ibs. 4 Ibs. Body surface Ill 106 97 103 95 88 Body measurements Depth at front end of keel 100 100 101 99 93 Depth at rear end of keel 96 99 100 101 112 Breadth at hips 100 102 103 106 101 102 Length of keel 96 103 99 89 105 96 Length of drumstick 99 102 101 100 91 87 98 100 99 99 86 84 Length of middle toe 98 98 101 93 87 86 Distance from rump to shoulder. . Midcircumference 101 103 102 100 103 101 103 104 98 104 95 97 average linear measurements of the six weight groups of pullets have been expressed as percentages of the corresponding average measure- ments of the cockerel groups of the same weight. The linear differ- ences between pullets and cockerels were not marked except for the three leg measurements for the 3- and 4-pound weights; in these cases, the cockerels surpassed the pullets. In breadth at hips, the pullets were consistently larger, on the average, than the cockerels, and in mid-circumference they were larger except at the 4-pound weight. SURFACE AREA AT DIFFERENT AGES The significance of the determination of the surface area of ani- mals relates to the basal heat production. That the basal heat pro- duction of animals of a given species and age is more closely related to body surface than to any other measurement of size, including body weight, has been repeatedly demonstrated. Skin Areas of the Birds. The surface area of the White Leghorn chickens examined in this investigation was determined by measuring the area of the skin after removal from the body. The skin was re- moved and cut in such a way that it could be flattened out evenly on paper. It was then stretched at as uniform a tension as possible, pinned down to the paper, and outlined with a pencil. The area within the outline was measured with a planimeter. The areas of the skins were determined in this way in order to 1931} GROWTH OF WHITE LEGHORN CHICKENS 97 obtain fairly reproducible values. The great elasticity of chicken skin is a formidable obstacle to its use for this purpose and the de- gree of accuracy of any individual area measurement is not great, altho the accuracy of an average of 10 measurements on birds of approximately the same weight is presumably over three times as great. In all probability the average skin area for each group of 10 birds is only approximately equal to the corresponding body surface. However, the ratio of skin area (as determined) to body surface may be fairly constant, in which case the skin area can be used for most purposes as a satisfactory unit of reference for basal heat production. For the larger birds the surface area of the combs and wattles was also determined as being equal to twice the outlined area. The aver- age results of these measurements have been assembled in Table 10. TABLE 10. AVERAGE SKIN AREAS OF WHITE LEGHORN CHICKENS OF DIFFERENT WEIGHTS AND SEX (Each figure is an average of 10 birds) Cockerels Pullets Body weight Skin area Area of combs and wattles 1 Total Body weight Skin area Area of combs and wattles 1 Total gms. sq. cms. sq. cms. sq. cms. gms. 53. cms. sq. cms. sq. cms. 31. 1* 86 86 218 294 294 222 325 325 477 568 568 468 602 602 678 840 36 876 669 815 815 874 986 66 1 052 890 1 016 1 016 1 317 1 367 116 1 483 1 367 1 298 34 1 332 1 719 1 536 124 1 660 1 716 1 350 72 1 422 2 136 1 689 160 1 849 'The areas given are twice the areas outlined. 2 The sex of these birds was not determined. Estimation of Skin Area by Mathematical Formula. In using these data for the development of a formula for the estimation of surface, the areas of combs and wattles have not been considered. The growth of these appendages is largely a sex characteristic, and the ratio of the area thus added to the added weight is of an entirely different order from the ratio of surface to weight for the remainder of the body. Furthermore, the growth of comb and wattles is readily influenced by environmental conditions. Birds raised indoors, for example, will show a much greater development of these appendages than birds raised outdoors. It seemed hopeless, therefore, to expect to find a formula involving body weight, or body weight and some linear body measurement, that would satisfactorily estimate a surface area inclusive of the area of combs and wattles. 98 BULLETIN No. 367 [April, From the average body weight and the average skin area of each group of birds, the constant k in the Meeh equation, 5 = kW^, was calculated, with the results given in Table 11,5 being the surface area in square centimeters and W the body weight in grams. TABLE 11. MEEH CONSTANTS FOR EACH GROUP OF WHITE LEGHORN CHICKENS Weight group Cockerels Pullets Ibs. At hatching 8.70 .5 8.12 8.86 1 9 30 9 99 1.5 10.88 10.65 2 10.79 10.98 3 11 40 10 81 4 10.70 9.92 5 10.18 Evidently the unmodified Meeh formula will not apply thruout the weight range of these birds, tho for birds above a weight of 1 pound a satisfactory application of the formula seemed possible. For birds of both sexes a constant of 10.39 seemed to give the best fit. The estimates of area by the Meeh equation with this value of k, and the deviations from the observed areas will be found in Table 12. Applying to the data a formula involving a linear body measure- ment as well as weight, of the type used in the previous study of the growth of White Plymouth Rock chickens, gave the estimates of TABLE 12. ESTIMATED SURFACE AREAS OF WHITE LEGHORN CHICKENS BY MEEH FORMULA: 5 = 10.39 W - 667 Average body weight (W) Observed surface area Estimated surface area (5) Deviations Absolute Percentage Cockerels gms. 31i sq. cms. 86 sq. cms. 103 sq. cms. + 17 +19.8 218 294 376 + 82 +27.9 477 568 634 + 66 +11.6 678 840 802 - 38 - 4.5 874 986 950 - 36 - 3.7 1 317 1 367 1 245 -122 - 8.9 1 719 1 536 1 491 45 2.9 2 136 1 689 1 723 + 34 + 2.0 Pullets 222 325 381 + 56 +17.2 468 602 626 + 24 + 4.0 669 815 795 - 20 - 2.5 890 1 016 961 - 55 - 5.4 1 367 1 298 1 281 - 17 - 1.3 1 716 1 350 1 489 + 139 + 10.3 iThe sex of this group was not determined. 1931} GROWTH OF WHITE LEGHORN CHICKENS 99 surface contained in Table 13. The formula used was 5 = 6.01W- 5 L- 6 , in which L is the distance from rump to shoulder in centimeters. This measurement, related to body length, can be determined with considerable accuracy. The total body length of a live chicken, from tip of beak to rump, is not, in our experience, susceptible to accurate TABLE 13. ESTIMATED SURFACE AREAS OF WHITE LEGHORN CHICKENS BY FORMULA: 5 = 6.01 W* L- 8 Average body weight (W) Distance from rump to shoulder (L) Observed surface area Estimated surface area (S) Deviations Absolute Percentage Cockerels gms. 31 1 cms. 4 7 sq. cms. 86 53. cms. 85 sq. cms. 1 1 2 218 9.6 294 345 + 51 +17 3 477 13.0 568 612 + 44 + 77 678 14.9 840 791 - 49 5.8 874 16.0 986 938 48 4 9 1 317 19.0 1 367 1 276 91 6.7 1 719 20 4 1 536 1 522 14 9 2 136 21.3 1 689 1 741 + 52 + 3.1 Pullets 223 9.7 325 351 + 26 + 80 468 13.0 602 606 + 4 + .7 669 14 9 815 786 29 3 6 890 16.5 1 016 964 52 5.1 1 367 18.6 1 298 1 284 - 14 - 1.1 1 716 19.3 1 350 1 471 + 121 + 9.0 : The sex of these birds was not determined. measurement, since it varies so much with the tension used in stretch- ing out the bird. The estimations of surface area by the weight-length formula are not greatly superior to those made by the use of the Meeh equation. For the eleven groups of birds weighing 1 pound or over, the average percentage deviation of the estimated from the observed areas, neg- lecting signs, was 4.42 by the weight-length formula and 5.19 by the Meeh formula. In all probability a satisfactory formula for the estimation of the surface area of chickens can be obtained only from direct measure- ments of the body surface by some such method as that used by Cowgill and Drabkin 5 * for the dog. Direct Determination of Surface Area. Some time after the con- clusion of this experiment it was decided to attempt the direct deter- mination of the surface area of White Leghorn chickens by a mold method. Satisfactory results were secured upon 25 chickens, varying in body weight from 109 to 2,142 grams. The method used was as follows. 100 BULLETIN No. 367 [April, The birds were killed by bleeding and debraining, and were then dry picked. They were next measured and laid out in a standard supine position with neck and wings extended and legs as nearly con- tracted as the method of molding permitted. The wings were pinned down in the desired position, and the legs were supported on strings suspended from a laboratory ring stand. The comb and wattles were then cut off, as were the ear lobes in the larger birds. The surface of the bird was then covered closely with strips of ordinary medical sterilized gauze, either 2 inches or 1 Inch in width, which were made to adhere to the body and to each other by collodion applied with a brush. By varying the size of gauze and the length of the strip, it was possible to cover all parts of the body regardless of their curva- ture. The shanks and feet, however, were not covered. After the ventral part of the body was covered, the bird was turned over and covered on the dorsal side without changing the position of legs and wings. The completed mold was dry in an hour or less, during which time a slight contraction of the gauze occurred insuring a tight fit. In removing the mold from the body, it was first cut in two parts along the median sagittal line, and then was cut along the neck, wings, and legs as necessary for convenient removal. After removal from the body, the mold was cut into pieces of such size and shape that they would lie flat. The pieces were outlined with a pencil on a large sheet of paper and their combined area was determined with the planimeter. The mold was cut into 17 to 50 pieces, the number depending upon the size of the bird. The comb and wattles were also outlined and the area doubled, allowance being made in the case of the comb for the area of the surface of attachment to the head. The ear lobes, when large enough to require separate treatment, were outlined and meas- ured, and allowance was made for the area of attachment. The area of the shanks and feet was determined by skinning one shank and foot, determining the area of the skin by cutting up, outlining, and applying the planimeter, and doubling this area. For a number of the birds the areas of the two halves of the carcass were determined separately in order to ascertain the accuracy of the method. In Table 14 the mold areas of the two halves of all chickens on which this test was made are compared. Evidently the method is capable of close duplication, within 2 percent, when the mold is fitted to the carcass in a standard position. In other tests it was clearly shown that the surface area of the extended leg or wing is considerably greater than that of the same member contracted, and that the differ- ence is not due to the' formation of folds or wrinkles of skin in the latter position. 1931} GROWTH OF WHITE LEGHORN CHICKENS 101 Besides the live weight and surface area three linear measure- ments were taken on the picked carcass: (a) the over-all length, from tail to tip of beak, (b) the rump-to-shoulder length, and (c) the cir- cumference of thorax taken over the keel and just behind the wings. On many of the birds the picked, bled weight was also recorded. These measurements and weights are all contained in Table 15. TABLE 14. SURFACE AREAS OF MOLDS FROM RIGHT AND LEFT HALVES OF WHITE LEGHORN CHICKENS* Bird No. Sex Body weight Surface area Difference Left side Right side 22 24 25 26 27 28 29 Pullet gms. 1 074 1 799 1 978 1 458 1 653 1 841 2 142 sq. cms. 483 646 693 580 628 651 728 sq. cms. 491 659 707 580 625 641 729 perct. 1.64 1.99 2.00 .48 1.55 .14 Cockerel . Cockerel Cockerel Cockerel . Cockerel Cockerel 'Exclusive of shanks and feet and of combs and wattles. TABLE 15. BODY WEIGHTS, SURFACE AREAS, AND BODY MEASUREMENTS OF WHITE LEGHORN CHICKENS Bird No. Sex Body weight Surface area Length over all Rump to shoulder Circum- ference Picked _ weight 8 gms. 110 sq. cms. 227 cms. 18 cms. 7.4 cms. 11 gms. 9 109 220 18 7.4 10.5 11 235 376 25 9.1 14 12 m 341 526 27.5 11.1 15 13 m 449 618 29 11.8 17 14 m 555 731 33 13.2 18 490 15 m 578 781 33.5 13.2 19.5 504 16 f 668 795 35 5 13.7 19.5 570 21 f 840 908 39.5 16.1 22.5 712 18 f 984 1 014 39.5 17.0 23.5 861 23 f 1 059 1 038 42 16.5 24 920 17 m 1 072 1 155 40.5 16.7 23.5 948 22 f 1 074 1 127 44 5 16.8 24.5 937 20 f 1 109 1 174 41 16.9 23.5 947 19 f 1 213 1 152 41.5 17.6 25 1 095 5 f 1 273 1 172 40.5 16.0 24.5 1 121 7 f 1 329 1 247 45 17.2 25 26 1 458 1 470 45.5 18.5 26.5 1 270 6 f 1 495 1 469 46 29.5 10 f 1 513 1 435 47 18.2 27 27 m 1 653 1 602 48 18.9 28.5 1 423 24 m 1 799 1 684 48 19.4 27.5 1 612 28 m 1 841 1 612 48 18.0 28 1 600 25 m 1 978 1 720 50.5 19.9 29 1 725 29 m 2 142 1 894 49.5 21.3 30 1 918 Prediction Formulas for Surface Area. In attempting to fit a prediction formula to these measurements of surface area, it was realized that a close fit was hardly to be expected, because of a vari- able feather coat which would affect body weight but not body sur- face as measured from the picked carcass, and because of a variable 102 BULLETIN No. 367 [April, growth of comb and wattles, the size of these parts depending in particular on sex and to some extent on nutritive condition. An ex- tensive growth of comb and wattles would increase the body weight somewhat, but would have an entirely disproportionate effect upon surface area. Using the method of least squares, the Meeh formula, 5 = kW M7 , was fitted to the data in Table 15, with the result that k was evaluated at 10.64. The areas of the birds calculated by means of this constant are given in Column 4 of Table 16, and the percentage deviations TABLE 16. COMPARISON OF CALCULATED AND OBSERVED SURFACE AREAS OF WHITE LEGHORN CHICKENS Bird No. Sex Observed surface area S = 10.64 W- Difference 5 = 8.19 PF-* Difference w-**> L 8.. . sg. cms. 227 sq. cms. 244 perct. + 7.49 sg. cms. 226 perct. .44 .266 9 220 243 +10.45 224 +1.82 .265 11 m 376 405 + 7 71 385 +2 39 247 12 m 526 519 1.33 501 4.75 .254 13 618 624 + 97 608 1 62 .264 14 m 731 718 1.78 707 3 28 .249 15 781 738 5 51 727 6 91 249 16 f 795 813 + 2 26 805 +1 26 .246 21 f 908 947 + 4.30 946 +4.18 .239 18 f 1 014 1 052 + 3 75 1 058 +4 33 252 23 f 1 038 1 105 + 6.45 1 115 +7.42 .243 17 1 155 1 114 3 55 1 124 2 68 253 22 f 1 127 1 115 1 06 1 126 .09 .230 20 f 174 1 140 2.90 1 151 -1.96 .252 19 f 152 1 210 + 5 03 1 227 +6 51 .257 5 f 172 1 249 + 6.57 1 269 +8.28 .268 7 f 247 1 286 + 3.13 1 308 +4.89 .244 26 m 470 1 368 6 94 1 396 5.03 .249 6 f 469 1 391 5.31 1 421 -3.27 .249 10 f 435 1 402 2 30 1 433 .14 .244 27 m 602 1 487 7.18 1 526 -4.74 .246 24 684 1 573 6 59 1 620 3 80 .253 28 m 1 612 1 598 .87 1 646 +2.11 .255 25 1 720 1 676 2 56 1 732 + .70 .249 29 m 1 894 1 767 6 71 1 832 -3.27 .260 Average 4.51 3.73 .251 from the observed values in Column 5. The average percentage deviation, disregarding signs, is 4.51. If the exponent of W (body weight in grams) in the Meeh formula, as well as its coefficient k, be evaluated from the data by the method of least squares, the prediction formula becomes 5 = 8.19W- 705 . The calculated areas of the birds by this formula and the percentage deviations are given in Columns 6 and 7 of Table 16. The average percentage deviation is 3.73, somewhat less than that obtained with the first formula, and the fit to the data is appreciably better at the two ends of the range. The second formula is thus a distinct improve- ment over the first. Of the 25 cases only 5 show deviations greater 1931} GROWTH OF WHITE LEGHORN CHICKENS 103 than 5 percent, and all are within 10 percent. Closer fits of prediction formulas to surface-area measurements have been obtained with other animals but, as already explained, the prospects of obtaining a close fit of any formula to surface-area measurements in chickens are not encouraging. An attempt was made to improve the formula by the introduction of a term defining the nutritive condition of the animal. According to TABLE 17. AVERAGE WEIGHTS OF PARTS OF CARCASSES OF WHITE LEGHORN COCKERELS KILLED AT DIFFERENT WEIGHTS (Each figure is an average of 10 birds; all weights in grams) Approximate slaughter weight Hatching weight .5 Ib.i 1 Ib. 1.5 Ibs. 2 Ibs. 3 Ibs. 4 Ibs. 5 Ibs. 2 44 58 72 86 107 156 219 31.1 218 477 678 875 1 317 1 719 2 136 Viscera and offal Blood 1.07 8 00 19 4 27 6 32 8 53 8 79 109 Feathers i 11 6 35 6 55 9 65 7 88 5 134 179 Head 4 15 13 21 1 28 7 39 1 61 9 69 5 84 8 1 35 10 5 23 32 41 9 63 6 71 7 84 7 Heart .231 1.75 2 65 3 38 4 09 6 12 7 96 11 5 Liver 1.06' 7 02 12 6 15 8 20 24 5 34 44 5 226 2 98 5 32 6 10 7 70 8 71 11 30 13 7 Pancreas 085 97 1 92 2 10 2 26 3 16 3 90 4 58 Spleen .016 31 71 1 10 1 60 2 25 2 69 3 59 268 1 42 2 62 3 59 4 20 6 87 9 29 10 3 Testicles 074 20 39 3 44 7 18 5 55 4 80 Intestinal tract exclu- sive of gizzard. . . 2.55 1 67 19.5 8 39.6 14 3 49.9 19 8 58.8 20 6 78.0 28 9 101 38 6 106 43 4 Contents of digestive tract 3 . 56< 9 4 16 6 20 5 21 1 32 3 42 1 61 8 Dressed carcass Neck 1 04 7 5 16 6 21 3 27 4 42 9 52 59 i Skin 3 24> 14 8 30 42 6 54 9 87 7 120 138 Legs above hock .... Wings 3.47 77 32.5 13 9 79.4 31 9 124 45 9 168 60 272 93 7 350 113 448 133 Torso 3.55 42 8 107 158 214 327 446 553 Total bone in carcass (except head, shanks, and feet) 11 8 s 34 4 75 2 95 8 131 200 ^46 297 Total flesh and fat in carcass (except head, shanks, and feet) .... 56.0 150 237 327 517 695 862 1 Average for 11 birds. 1 2 The feathers were not removed from the skin. 3 This weight includes the weight of the gall bladder. Yolk sac + contents. 5 Bones were not separated from the flesh. Cowgill and Drabkin, 5 * a term that should serve this purpose is ob- tained by dividing the cube root of the body weight by the body length. In the last column of Table 16, this factor, involving the length in centimeters from tail to tip of beak, is given for each bird. If this factor is capable of serving a useful purpose in improving a prediction formula involving only the body weight, the nutritive factor would be expected to be out of line for birds whose calculated areas deviated most widely from the observed. But a comparison of the last two columns in Table 16 does not reveal such a situation. The 104 BULLETIN No. 367 [April, greatest positive deviation, 8.28 percent, it is true, is associated with the highest nutritive correction factor, .268, but the next highest factor, .266, is obtained with a bird (No. 8) for which a very close prediction of surface area was obtained; this is also true of the two TABLE 18. AVERAGE WEIGHTS OF PARTS OF CARCASSES OF WHITE LEGHORN PULLETS KILLED AT DIFFERENT WEIGHTS (Each figure is an average of 10 birds; all weights in grams) Approximate slaughter Hatching .5 lb. 1 Ib. 1.5 Ibs. 2 Ibs. 3 Ibs. 4 Ibs. 2 44 58 72 100 159 233 Live weight 31.1 223 468 669 890 1 367 1 716 Viscera and offal Blood 1 07 8 35 18 9 25 4 31 9 50 9 58 9 Feathers i 13 7 39 5 56 3 78 4 102 97 2 Head 4.15 11 7 18 6 23 1 27 7 38 44 7 1 35 9 82 21 5 29 9 35 3 42 8 45 4 Heart 231 1 39 2 28 2 79 3 40 5 13 6 73 Liver 1.06' 6.32 11.2 14.9 17.7 24.4 31 7 226 2 85 4 69 6 08 7 23 9 61 11 4 Pancreas 085 1.02 1 80 1.97 2 52 3 21 3 23 016 35 85 1 14 1 57 2 62 2 15 268 1 46 2 38 3 33 4 66 5 87 6 53 Ovaries 4 3.72 42 3 Intestinal tract exclu- sive of gizzard Gizzard 2.55 1.67 18.7 8.74 36.2 14.5 46.4 20.4 62.0 25.4 99.7 34.8 124 39.0 Contents of digestive tract 3.56 s 11 14.9 20 23 8 33.9 38.8 Dressed carcass Neck 1.04 7.43 15.4 20.8 27.1 35.5 39.3 Skin 3 24* 14 4 28 4 39 9 56 1 98 5 129 Legs above hock 3.47 31.9 80 6 120 163 250 304 Wings .77 14.2 33.1 46.9 . 62.9 85.0 95.9 Torso 3 55 47 8 109 165 236 410 549 Total bone in carcass (ex- cept head, shanks, and feet) 11 8 32 8 68 7 102 124 166 197 Total flesh and fat in car- cass (except head, shanks, and feet).. . . 62.6 160 239 354 593 764 >Average for 9 birds. *The feathers were not removed from the skin. 'This weight includes the weight of the gall bladder. 4 This includes the weight of oviduct. 6 Yolk sac + contents. 6 Bones were not separated from the flesh. next highest factors, .265 and .264. The lowest nutritive factor, .230, is also associated with a bird for which a very good prediction was secured. These considerations do not indicate that the cause of the poor predictions obtained by using the second prediction formula was a variable nutritive condition of the birds. Hence no systematic at- tempt was made to introduce this factor into the prediction formula. Sex Differences. From the fact that the six largest positive per- centage deviations of predicted from observed areas relate to females, while the five largest negative deviations relate to males, it seems evi- dent that sex is a determining factor in surface area, even before excessive comb growth is present (Nos. 12 and 15). Unfortunately 1931] GROWTH OF WHITE LEGHORN CHICKENS 105 the present data are not suitable for the derivation of separate pre- diction formulas for each sex, since the females measured are all of intermediate weight, while the males are, with two exceptions, either lighter than 578 grams or heavier than 1,653 grams. RELATIVE AND ABSOLUTE GROWTH OF VISCERA AND OF DIFFERENT PARTS OF CARCASS A number of the larger visceral organs from each of the slaughtered birds and of certain more or less well-defined parts of the carcass were weighed in this investigation. The average weights, each representing 10 individual weights, have been summarized in Tables 17 and 18. TABLE 19. AVERAGE WEIGHTS OF PARTS OF CARCASSES OF WHITE LEGHORN COCKERELS KILLED AT DIFFERENT WEIGHTS, EXPRESSED IN PERCENTAGE OF EMPTY BODY WEIGHT (Each figure is an average of 10 birds) Approximate slaughter Hatching .5 Ib. 1 Ib. 1.5 Ibs. 2 Ibs. 3 Ibs. 4 Ibs. 5 Ibs. Age in days 2 44 58 72 86 107 156 219 Percentage "fill" 11 4 4.3 3 5 3.0 2.4 2.5 2.4 2.9 Empty weight in grams Offal Feathers 27.5 i 209 5.55 460 7.74 658 8.50 854 7.69 1 285 6.89 1 677 7.99 2 074 8.63 Blood 3 89 3.83 4.22 4.19 3.84 4.19 4.71 5.26 Head 15.1 6.22 4.59 4.36 4.58 4.82 4.14 4.09 4 91 5 02 5 00 4 86 4 91 4.95 4.28 4.08 Total offal 23 9 20 6 21.6 21.9 21.0 20.8 21.1 22.1 Viscera Heart .84 .84 .58 .51 .48 .48 .47 .55 Liver 3 85 3 36 2 74 2.40 2.34 1.91 2.03 2.15 Kidneys .82 1.43 1.16 .93 .90 .68 .67 .66 Pancreas .31 .46 .42 .32 .26 .25 .23 .22 Spleen 06 .15 .15 .17 .19 .18 .16 .17 Lungs .97 .68 .57 .55 .49 .53 .55 .50 Testicles .04 .04 .06 .40 .56 .33 .23 Digestive tract 15 3 13.2 11.7 10.6 9.30 8.32 8.32 7.20 Total viscera 22.1 20.2 17.4 15.5 14.4 12.9 12.8 11.7 Dressed carcass Skin 11 81 7 08 6.52 6.47 6.43 6.82 7.16 6.65 Neck 3.78 3.59 3.61 3.24 3.21 3.34 3.10 2.85 Legs above hock .... Wings 12.6 2 80 15.6 6 65 17.3 6.93 18.8 6.98 19.7 7.03 21.2 7.29 20.9 6.74 21.6 6.41 Torso 12.9 20.5 23.3 24.0 25.1 25.4 26.6 26.7 Total dressed carcass Total bone in dressed carcass 43.9 42.9' 53.4 16.5 57.7 16.3 59.5 14.6 61.5 15.3 64.0 15.6 64.5 14.7 64.2 14.3 Total flesh and fat in dressed carcass .... 26.8 32.6 36.0 38.3 40.2 41.4 41.6 Total flesh, fat, edible viscera 1 and skin.. . 53.6 41.9 45.5 48.4 49.9 51.7 53.5 53.0 feathers were not removed from the skin for this group of birds. 2 This includes the gall bladder. 'Bones and flesh were not separated for this group. 'Including heart, liver and gizzard. These weights are expressed as percentages of the corresponding empty body weights in Tables 19 and 20. The average weights of all organs and parts increased progressive- ly in absolute value as the body weight increased, with few exceptions, 106 BULLETIN No. 367 [April, the significance of which is evidently negligible when the individual weights are consulted. The relative weight of the offal parts (feathers, blood, head, and shanks and feet) remained fairly constant for the cockerels after a body weight of .5 to 1 pound was reached. The TABLE 20. AVERAGE WEIGHTS OF PARTS OF CARCASSES OF WHITE LEGHORN PULLETS KILLED AT DIFFERENT WEIGHTS, EXPRESSED IN PERCENTAGE OF EMPTY BODY WEIGHT (Each figure is an average of 10 birds) Approximate slaughter weight Hatching weight .5 Ib. 1 Ib. 1.5 Ibs. 2 Ibs. 3 Ibs. 4 Ibs. 2 44 58 72 100 159 233 11 4 4 9 3 2 3 2 7 2 5 2 3 Empty weight in grams. . Offal Feathers 27.5 i 212 6.46 453 8.72 649 8.67 866 9.05 1 333 7.65 1 677 5.80 Blood 3 89 3 94 4 17 3 91 3 68 3 82 3 51 Head 15.1 5.52 4.11 3.56 3 20 2 85 2 67 4 91 4 63 4 75 4 61 4 08 3 21 2 71 Total offal 23 9 20 5 21.7 20 7 20 17 5 14.7 Viscera Heart .84 .66 .50 .43 .39 .38 .40 Liver 3 85* 2 98 2 47 2 30 2 04 1 83 1 89 Kidneys .82 1.34 1.04 .94 .83 .72 .68 Pancreas .31 .48 .40 .30 .29 .24 .19 .05 .17 .19 .18 18 .20 .13 Lungs .97 .69 .53 .51 .54 .44 .39 Ovaries* .28 2.52 Digestive tract 15 3 12 9 11 2 10 3 10 1 10 1 9.72 Total viscera 22.1 19.2 16.3 15.0 14.4 14.2 15.9 Dressed carcass Skin 11.81 6.79 6.27 6.15 6.48 7.39 7.69 Neck 3 78 3 50 3 40 3 20 3 13 2.66 2.34 12 6 15 17 8 18 5 18 8 18 8 18.1 2 62 6 70 7 31 7 33 7 26 6.38 5.72 Torso 12.9 22.5 24.1 25.4 27.3 30.8 32.7 Total dressed carcass . . Total bone in dressed car- 43.7 42 9 54.5 15 5 58.9 15 2 60.5 15 7 63.0 14 3 66.0 12.5 66.6 11.7 Total flesh and fat in 29 5 35 3 36 8 40 9 44.5 45.6 Total flesh, fat, edible viscera 5 and skin. . . . 44.1 47.8 48.8 52.6 56.7 57.9 'The feathers were not removed from the skin for this group of birds. 'This includes the gall bladder, includes weight of oviduct. 4 Bones and flesh were not separated for this group, including heart, liver, and gizzard. average percentage weights of the sum of these parts varied for all weights from 20.6 to 23.9. For the pullets the offal parts decreased in relation to the empty weight at the higher body weights of 3 and 4 pounds. The relative weight of blood, however, did not share in this tendency. Percentage Increases in Organ Weights. The percentage weights of viscera showed a general tendency to decrease with age, tho fre- quently in an irregular manner. This decrease was most marked for the younger ages. The percentage weight of the spleen in both sexes showed little tendency to variation aside from a marked increase from 1931} GROWTH OF WHITE LEGHORN CHICKENS 107 hatching to the .5-pound weight. The cockerels seem to be clearly distinguished from the pullets by a more rapid decrease in the per- centage weight of the digestive tract. Beyond the 1.5-pound weight the pullets possessed a larger average weight of digestive apparatus, TABLE 21. RELATIVE INCREASE IN WEIGHT OF PARTS OF CARCASSES OF WHITE LEGHORN COCKERELS WITH INCREASE IN BODY WEIGHT (Expressed in percentage) Approximate slaughter weight ' .51b. 1 Ib. 1.5 Ibs. 2 Ibs. 3 Ibs. 4 Ibs. 5 Ibs. 44 58 72 86 107 156 219 Offal Feathers 100 307 482 566 763 1 155 1 543 Blood 100 243 345 410 673 988 1 363 Head 100 162 221 301 476 535 652 Shanks and feet 100 219 305 399 606 683 807 Total offal 100 230 335 416 621 822 1 061 Viscera Heart 100 151 193 234 350 455 657 Liver 100 179 225 285 349 484 634 100 179 205 258 292 379 46O Pancreas 100 198 216 233 326 402 472 Spleen 100 229 355 516 726 868 l 158; 100 185 253 296 484 654 725 Digestive tract 100 196 253 289 389 508 545 100 190 243 284 378 498 567 Dressed carcass Skin 100 203 288 371 593 811 932 Neck 100 221 284 365 572 693 788 Legs above hock 100 244 382 517 837 1 077 1 378 Wings 100 229 330 432 674 813 957 Torso 100 250 369 500 764 1 042 1 292 Total dressea carcass. . Total bone in dressed carcass 100 100 238 219 351 278 470 381 738 581 970 715 1 194 863 Total flesh and fat in dressed carcass Total flesh, skin, fat, and edible viscera 100 100 268 239 423 364 584 488 923 759 1 241 1 024 1 539 1 256 both absolute and relative, than the cockerels. The weight of heart was, on the average, always greater for the cockerels than for the pullets. The total weight of dressed carcass increased slowly with increas- ing body weight for the cockerels, and appreciably faster for the pullets. At all weights the dressed carcasses of the females averaged heavier than those of the males, owing entirely to additional muscular and fatty tissue. For weights above 1.5 pounds the bones in the dressed carcasses of the males outweighed the bones in the females. These comparisons of the weights of organs and parts of carcass for birds of different weights and different sex are presented in Tables 21,22, and 23 in a different manner. For the body-weight comparison the weights of the organs and parts of the .5-pound birds, the lightest birds for which complete dissection of the parts was made, are taken 108 BULLETIN No. 367 [April, TABLE 22. RELATIVE INCREASE IN WEIGHT OF PARTS OF CARCASSES OF WHITE LEGHORN PULLETS WITH INCREASE IN BODY WEIGHT (Expressed in percentage) Approximate slaughter weight 5 Ib. Age in days 44 Offal Feathers 100 Blood 100 Head 100 Shanks and feet 100 Total offal 100 Viscera Heart 100 Liver 100 Kidneys 100 Pancreas 100 Spleen 100 Lungs 100 Digestive tract 100 Total viscera 1 100 Dressed carcass Skin 100 Neck 100 Legs above hock 100 Wings 100 Torso 100 Total dressed carcass 100 Total bone in dressed carcass 100 Total flesh and fat in dressed carcass 100 Total flesh, skin, fat, and edible viscera 100 'Exclusive of reproductive organs. 1 Ib. 1.5 Ibs. 2 Ibs. 3 Ibs. 4 Ibs. 58 288 226 159 219 226 164 177 165 176 243 163 185 181 197 207 253 233 228 230 209 256 72 411 304 197 304 310 201 236 213 193 326 228 244 238 277 280 376 330 345 339 311 382 339 100 572 382 237 359 397 245 280 254 247 449 319 319 305 390 365 511 443 494 471 378 565 159 745 610 325 436 537 369 386 337 315 749 402 489 454 684 478 784 599 858 760 506 947 233 709 705 382 462 564 484 502 400 317 614 447 595 523 896 529 953 675 1 149 966 601 1 220 TABLE 23. AVERAGE WEIGHTS OF PARTS OF CARCASSES OF WHITE LEGHORN PULLETS KILLED AT DIFFERENT WEIGHTS, EXPRESSED IN PERCENTAGES OF CORRESPONDING WEIGHTS FOR THE COCKERELS Approximate slaughter weight. .5 Ib. 1 Ib. 1.5 Ibs. 2 Ibs. 3 Ibs. 4 Ibs. Offal Feathers Blood Head Shanks and feet. Total offal Viscera Heart Liver Kidneys Pancreas Spleen Lungs Gizzard Digestive tract. Total viscera 1 . . Dressed carcass Skin Neck Legs above hock Wings Torso Total dressed carcass . Total bone in dressed carcass Total flesh and fat in dressed carcass Total flesh, fat, edible viscera, and skin. . . 118 104 90 94 101 79 90 96 105 113 103 109 96 97 97 99 98 102 112 104 95 112 111 97 93 99 86 89 88 94 120 91 101 94 93 95 93 102 104 102 100 91 107 103 101 92 80 93 93 83 94 100 94 104 93 103 96 95 94 98 97 102 104 100 106 100 100 119 97 71 84 97 83 88 94 112 98 111 123 110 104 102 100 97 105 110 104 95 108 115 95 61 67 87 84 100 110 102 116 85 120 126 117 112 83 92 91 125 107 83 115 73 75 64 63 70 85 93 101 83 80 70 101 117 101 108 76 87 85 123 103 80 110 108 Exclusive of reproductive organs. 1931} GROWTH OF WHITE LEGHORN CHICKENS 109 as 100, and all later weights are expressed as percentages of these. For the sex comparison the weights of organs and anatomical parts of the pullets are expressed as percentages of the corresponding parts of the cockerels. Sex Differences. Table 23 brings out in a particularly clear way the sex differences in anatomical makeup. The consistently greater weights of head (including comb and wattles), shanks and feet, and heart in the cockerels and the generally greater weights of blood and bones in the dressed carcasses are clearly evident. On the other hand, the females consistently exceeded the males in weights of gizzard, dressed carcass, and flesh and fat, and generally in weights of feathers. At the higher body weights, i.e., 2, 3, and 4 pounds, the weights of total digestive tract, total viscera, and skin were greater in the females than in the males. In a general way the relations just discussed, involving weights of organs and parts of carcasses of White Leghorn chickens, are similar to those found by Latimer 9 * in his study of the post-natal growth of this species. The Illinois studies, however, reveal a greater percent- age weight of skeleton and digestive tract for the higher body weights, and a smaller percentage weight of skin at all body weights. The in- crease in the percentage weight of the heart, starting at a body weight of about 1,400 grams, as noted by Latimer, 9 * is not clearly evident in the Illinois data, tho the cockerels showed some increase in this respect after a body weight of 1,677 grams. Variability of Organ Weights. The variability of the individual weights of organs and parts, as measured by the coefficient of varia- tion, is given in Table 24 for the cockerels and in Table 25 for the pullets (page 110). This value was not calculated for many of the organs of the 2-day chicks; unfortunately many of the smaller organs in this group were not weighed to two significant figures. The small variability in empty weight simply testifies to the restricted selection of birds in taking samples of 10. The great variability in spleen weight is noteworthy. In average variability at all weights, the pullets exceeded the cockerels except with respect to gizzard weights, weights of bones in the dressed carcass, and weights of feathers. CHEMICAL COMPOSITION OF BIRDS AT DIFFERENT BODY WEIGHTS Composition of Chemical Samples. Each sample of 10 chickens was analyzed in 4 composite samples consisting of (1) the feathers, (2) the total bones in the dressed carcass, (3) the total flesh and fat in the dressed carcass plus the skin and the edible viscera, including 110 BULLETIN No. 367 [April, TABLE 24. COEFFICIENTS OF VARIATION OF INDIVIDUAL WEIGHTS OF ORGANS AND PARTS OF CARCASSES FOR WHITE LEGHORN COCKERELS 2 days old .5 Ib. 1 Ib. 1.5 Ibs. 2 Ibs. 3 Ibs. 4 Ibs. 5 Ibs. Aver- age 7 5 S 6 2 1 1 8 1 8 1 7 1 7 4 9 3 39 Feathers 14 7 8 6 11 7 13 6 10 7 6 6 8 2 10 61 Blood . . 43 3 22 5 12 8 11 4 12 7 1 9 1 10 6 16 11 Pancreas 9 7 11 6 14 8 12 6 17 6 12 8 16 4 14 34 Spleen 27 3 16 7 34 1 16 6 24 1 20 3 39 9 29 35 21 2 13 9 8 5 6 7 7 6 5 10 3 8 4 10 20 Lungs and trachea 13.5 10 6 3 7 4 14 7 8 7 9 10 4 9 77 11 6 11 4 6 7 6 2 10 1 9 5 9 5 9 29 Intestines 13 6 6 5 4 1 4 6 12 6 10 3 6 3 14 2 9 04 Skin 6 5 4 3 9 7 5 6 8 8 5 11 7 7 75 Heart 19 3 14 5 5 7 20 5 8 2 10 6 8 2 11 3 12 29 Liver 8 4 7.2 4 4 12 2 8 4 1 15 1 8 49 14 10 4 12 5 14 3 10 9 13 5 5 8 17 5 12 36 Flesh in dressed carcass 12.1 7 2 3 7 4 8 4 8 3 9 8 1 6 37 Bones in dressed carcass 19.3 9.0 9.2 9.0 10.9 10 3 7 7 10.77 Testicles 33.8 32.4 42.8 68.3 38.3 91.7 87.5 56.40 TABLE 25. COEFFICIENTS OF VARIATION OF INDIVIDUAL WEIGHTS OF ORGANS AND PARTS OF CARCASSES FOR WHITE LEGHORN PULLETS 2 days old .5 Ib. 1 Ib. 1.5 Ibs. 2 Ibs. 3 Ibs. 4 Ibs. Aver- age 7 5 6 5 4 1 1 4 1 6 1 8 7 5 4 34 Feathers 9 8 11 6 12.7 12 9 2 5 7 10 18 Blood 43 3 15 9 14 6 11 8 8 2 36 9 10 7 20 20 Pancreas 9 3 10 9 14 5 20 7 15 18 6 15 47 Spleen 37.4 18 6 22.7 46.0 46.6 18 3 35 07 21 2 12 6 8 4 9 7 9 2 12 1 10 11 90 Lungs and trachea Esophagus and proven- 13.5 13.6 11 4 7.3 12 5 19.3 9 25.7 7 5 9.1 10.3 7.7 8 9 13.74 9 93 Intestines 13.6 10.5 6.0 9.1 8.5 10.7 10.8 9.88 Skin 14 2 5 8 9 4 8 1 5 8 20 8 10 68 Heart 19.3 12.7 13.7 8.6 19 11.3 9 7 13 41 Liver 9.5 7.9 10.0 7.0 9.6 15.4 9.90 Gizzard 14 11.4 10 4 9.8 6 6 8 a 15 10 74 Flesh in dressed carcass Bones in dressed carcass Ovaries 12.2 9.0 5.9 8.0 3.1 6.0 4.4 8.4 4.7 10.0 11.3 20.1 12.6 55.9 8.40 9.01 33.58 TABLE 26. CHEMICAL COMPOSITION OF FEATHERS OF WHITE LEGHORN CHICKENS Approximate body weight Dry substance Crude protein Ether extract Ash Calcium Gross energy per gram Cockerels Ibs. .5 perct. 59.16 perct. 54.41 perct. 2.18 perct. 1.91 perct. .110 gm. cals. 3 248 1 59 19 55 28 1.55 1.65 . 160 3 206 1.5 76.84 69.38 1.71 2.03 .251 4 194 2 65 38 62 12 1 32 1 49 .136 3 084 3 65.66 64.64 1.02 1.26 .090 3 138 4 60.64 58.38 1.07 1.03 .107 3 040 5 77.16 70.65 1.38 1.28 .123 3 866 Pullets .5... 61.65 57.43 2.20 1.76 .090 3 358 1 . 60 56 57.49 1.45 1.42 .103 3 222 1.5... 58.92 54.53 1.45 1.45 .116 2 791 2 . 62 71 60 58 1.13 1.11 .110 3 077 3 72.49 68.08 1.05 .90 .125 3 608 4 X4 . 66 74.62 1.06 1.25 .212 4 065 1931} GROWTH OF WHITE LEGHORN CHICKENS 111 liver, heart, and gizzard from which the inner membrane had been removed, and (4) the offal, including blood, head, shanks and feet, and all viscera not included in the preceding sample. The results of the chemical analysis of these samples are summarized in Tables 26 to 29. TABLE 27. CHEMICAL COMPOSITION OF BONE SAMPLES OF WHITE LEGHORN CHICKENS Approximate body weight Dry substance Crude protein Ether extract Ash Calcium Calcium in ash Gross energy per gram Cockerels Ibs. .5 perct. 38.29 perct. 19.77 perct. 3.67 perct. 13.12 perct. 4.71 perct. 35.9 gm. cals. 1 465 1 38.65 20.37 3.28 13.95 5.12 36.7 1 437 is 43 02 20 25 5.17 15.43 5.60 36.3 1 666 2 46.86 20.96 7.77 16.47 6.20 37.6 1 860 3 48.39 20.43 9.83 16.09 6.43 40.0 1 982 4. 49 87 20.74 10.30 16.17 6.97 43.1 2 080 5 51.30 22.74 8.52 18.78 7.13 38.0 2 078 Pullets .5 40.13 21.11 4.13 13.87 5.07 36.6 1 553 1. 39 88 20 20 3.57 14.81 5.35 36 1 1 427 1.5 42.87 19.91 5.06 14.61 5.55 38.0 1 746 2 48.00 20.12 9.51 16.74 6.45 38.5 1 978 3. 53 74 21 19 11.64 19.74 7.75 39.3 2 181 4 53.44 19.41 14.97 18.01 7.58 42.1 2 479 TABLE 28. CHEMICAL COMPOSITION OF SAMPLES OF FLESH AND EDIBLE VISCERA OF WHITE LEGHORN CHICKENS Approximate body weight Dry substance Crude protein Ether extract Ash Calcium Gross energy per gram Cockerels Ibs. .5... perct. 29.85 perct. 21.21 perct. 4.42 perct. 1.31 Perct. .041 gm. cals. 1 588 1 25 00 21.29 2.81 1.39 .029 1 444 1.5 27.42 22.02 4.17 1.17 .032 1 651 2 32 06 22 51 6.40 1.14 .024 1 766 3 29 75 22.17 6.34 1.07 .025 1 760 4 29.23 22.25 6.20 1.06 .026 1 814 5 28.87 23.30 4.20 1.09 .024 1 723 Pullets .5 . . 28 54 21.97 4.62 1.38 .042 1 694 1 25.21 21.97 2.59 1.36 .031 1 459 1.5 27.37 21.33 4.54 1.17 .032 1 627 2 30 72 21.08 7.06 1.07 .030 1 832 3 35.56 20.26 13.61 .99 .022 2 350 4 43.89 16.69 24.32 1.00 .018 3 259 The greater fat content of all pullet samples except the feathers, for all body weights above 1.5 pounds, is noteworthy. Also, in the pullet samples exclusive of the feathers the fat content increased with in- creasing body weight, the increase being the more rapid at the higher weights. The cockerel samples did not show such an increase above a body weight of about 2 pounds. 112 BULLETIN No. 367 [April, TABLE 29. CHEMICAL COMPOSITION OF OFFAL SAMPLES OF WHITE LEGHORN CHICKENS Approximate body weight Dry substance Crude protein Ether extract Ash Calcium Gross energy per gram Cockerels Ibs. .5 perct. 23.53 perct. 16.47 perct. 2.97 perct. 2.87 perct. .672 gm. cals. 1 239 1 22.32 17.20 2 66 2 56 590 1 214 1.5 24.61 17.19 3.95 3.09 760 1 320 2 26.40 17.51 4.96 3.00 .770 1 415 3 27.54 17.44 5.15 3 43 960 1 490 4 27.39 18.24 5.50 3.59 1.010 1 512 5 25.45 18.28 3.72 2.95 .892 1 432 Pullets .5 23 86 16 73 2 86 2 70 618 1 277 1 23 64 17.38 3 04 2 98 740 1 278 1.5 24 65 16 89 3 95 3 25 818 1 323 2 27 79 16 44 7 29 2 97 775 1 530 3 31.13 17.44 11.63 3 28 .870 1 989 4 37.50 14.18 20.19 1.67 .377 2 743 Composition of the Birds. From the relative weights of the dif- ferent samples for each group of chickens and from their chemical composition, the composition of the live birds was calculated. The results of these calculations are given in Table 30. From these results the percentage composition of the birds has been calculated on the live-weight, empty-weight, and fat-free (protoplasmic) bases, and the percentages have been summarized in Table 31. The more rapid fattening of the pullets as compared with the cockerels is clearly evi- dent from this table. The cockerels generally contained a greater concentration of ash and calcium even on the fat-free basis. TABLE 30. AVERAGE CHEMICAL COMPOSITION OF WHITE LEGHORN CHICKENS Approximate body weight Average live weight Dry substance Crude protein Ether extract Ash Calcium Gross energy Cockerels Ibs. .07 . . . gms. 31.1 gms. 6.61 gms. 4.77 gms. 1.29 gms. .59 gms. .14 cals. 39 .5 218 4 60 34 41 77 7 13 7 48 2 03 302 1 477.2 128 1 99 29 11.95 16 92 4 65 663 1.5 677 8 209 1 154 6 25 2? 24 36 6 77 1 121 2 874.8 292 1 198 1 47 92 33 22 9 80 1 473 3. 1 317 431 7 295 4 77 49 50 33 15 89 2 275 4 1 719 563 1 393 4 101 86 63 36 21 09 3 082 5 2 136.0 716.1 528.0 89.76 82.61 25.46 3 813 Pullets .07 31 1 6 61 4 77 1 29 59 14 39 .5 223 5 61 10 44 10 7 51 7 64 2 10 323 1 468 1 130 7 102 39 11 83 16 82 4 56 675 1.5 668.7 197 5 141 8 25 79 23 85 6 94 1 032 2 890 297 2 197 3 57 59 31 65 9 56 1 588 3 1 367.0 512 5 303 1 153 3 49 57 15 37 3 020 4 1 716.0 741.3 321.1 335.4 52.06 16.58 4 982 1931} GROWTH OF WHITE LEGHORN CHICKENS 113 TABLE 31. PERCENTAGE COMPOSITION OF WHITE LEGHORN CHICKENS AT DIFFERENT LIVE WEIGHTS Approximate body weight Dry substance Crude protein Ether extract Ash Calcium Gross energy per gram Live-weight basis (Cockerels) Ibs. .07... perct. 21.24 perct. 15.32 perct. 4.14 perct. 1.90 perct. .44 gm. cats. 1 253 .5 27.66 19.10 3.26 3.42 .93 1 399 1 26 84 20.81 2.50 3 55 97 1 390 1.5 30.84 22.80 3.68 3.59 1.00 1 654 2 33 39 22 64 5.48 3 80 1 12 1 684 3 32 78 22.44 5.88 3.82 1 21 1 725 4 32 76 22 89 5 92 3 69 1 23 1 793 5 33.52 24.72 4.20 3.87 1.19 1 785 (Pullets) .07 ; 21 24 15 32 4 14 1 90 44 1 253 .5 27 34 19.73 3.36 3.42 .94 1 445 1 27.93 21.87 2.53 3.59 .98 1 442 1.5 29 53 21 21 3 86 3 57 1 04 1 543 2 33.39 22.16 6.47 3.56 1.07 1 784 3 37.50 22.18 11.22 3.63 1.12 2 210 4 43.20 18.71 19.55 3.03 .97 2 904 Empty-weight basis (Cockerels) .07... 23.99 17.29 4.68 2.14 .50 1 415 .5 28 90 19 95 3 40 3 57 97 1 445 1 27 81 21 56 2 59 3 67 1 01 1 440 1.5 31.81 23.52 3.79 3.70 1.03 1 706 2 34 21 23 20 5 61 3 89 1 15 1 725 3 33 60 23 00 6 03 3 92 1.24 1 768 4 33.58 23.46 6.07 3.78 1.26 1 838 5 34.51 25.45 4.33 3.98 1.23 1 838 (Pullets) .07 23 99 17 29 4 68 2 14 .50 1 415 .5 28 75 20 75 3.53 3.60 .99 1 520 1 28.85 22.59 2.61 3.71 1.01 1 489 1.5 30 44 21 86 3 98 3 68 1.07 1 591 2 34 31 22 77 6.65 3.65 1.10 1 833 3 38 46 22 74 11 50 3 72 1.15 2 266 4 44.20 19.15 20.00 3.10 .99 2 971 Fat-free basis (Cockerels) .07 20.26 26.30 25.89 29.12 30.30 29.34 29.29 31.55 18.14 20.65 22.13 24.45 24.58 24.48 24.98 25.56 2.25 3.59 3.77 3.85 4.12 4.17 4.02 4.16 .52 1.00 1.04 1.07 1.22 1.32 1.34 1.29 .5 1 1.5 ... 2 3 4 5 (Pullets) .07 20.26 29.23 26.94 27.56 29.63 30.46 30.25 18.14 24.10 23.20 22.77 24.39 25.69 23.94 2.25 4.17 3.81 3.83 3.91 4.20 3.87 .52 1.15 1.04 1.11 1.18 1.30 1.24 .5 1 1.5 2 3 4 Percentage Distribution of Nutrients Among Chemical Samples. The percentage distribution of the dry matter, crude protein, ether extract, gross energy, ash, and calcium among the four composite 114 BULLETIN No. 367 [April, TABLE 32. PERCENTAGE DISTRIBUTION OF DRY SUBSTANCE AND CRUDE PROTEIN AMONG COMPOSITE SAMPLES ANALYZED IN WHITE LEGHORN CHICKENS OF DIFFERENT WEIGHTS AND SEX Approximate body weight Dry substance Crude protein Flesh Bone Offal Feathers Flesh Bone Offal Feathers Cockerels /6s. .5 perct. 43.7 perct. 21.5 perct. 22.4 perct. 12.4 perct. 44.8 perct. 16.0 perct. 22.6 perct. 16 6 1 40.9 22.7 20.0 16.4 44.9 15.4 19.9 19.8 1.5 41.8 19.7 17.9 20 6 45 4 12.5 17 25 1 2 46.8 21.1 17.4 14.7 48.5 13.9 17.0 20 6 3 ... 45 8 22 5 18 3 13 4 49 8 13 9 16 9 19 4 4 46 5 21.8 17.3 14.4 50.7 12.9 16 5 19 9 5 44.3 21.3 15.1 19.3 48.5 12.8 14.7 24.0 Pullets .5 43.1 22.1 21.4 13.4 45.9 16 1 20 7 17 3 1 41.7 21.0 19.1 18.2 46.3 13.6 17.9 22.2 1.5 43 9 22 1 17 2 16 8 47 6 14 3 16 5 21 6 2 47.2 20.0 16.3 16.5 48.8 12 6 14 5 24 1 3 52 5 17 4 15 7 14 4 50 5 11 6 14 9 23 4 57.5 14.2 17.2 11.1 50.5 11.9 15.0 22.6 samples analyzed is shown in Tables 32 to 34. From these tables it is interesting to note that the edible meat of the heavier birds, i.e., birds weighing from 3 to 5 pounds, contained from 45 to 57 percent of the total dry matter, about 50 percent of the crude protein, from 51 to 70 percent of the fat, but only 14 to 18 percent of the ash, and only a little over 1 percent of the calcium in the entire carcass. The feathers contained one-fifth or more of the crude protein in the total carcass. In the heavier cockerels the bones contained about one-fourth of the fat in the body, but in the heavier pullets they contained a much TABLE 33. PERCENTAGE DISTRIBUTION OF ETHER EXTRACT AND GROSS ENERGY AMONG COMPOSITE SAMPLES ANALYZED IN WHITE LEGHORN CHICKENS OF DIFFERENT WEIGHTS AND SEX Approximate body weight Ether extract Gross energy Flesh Bone Offal Feathers Flesh Bone Offal Feathers Cockerels Ibs. .5 perct. 54.8 perct. 17.4 perct. 23.9 perct. 3.9 Perct. 46 3 perct. 16.5 perct. 23.5 perct. 13.5 1 49 2 20 7 25 5 4 6 45 5 16 2 20 9 17 1 1.5 52.7 19 6 23 9 3.8 46.9 14 2 17.9 20 8 2 56 9 21 3 20 1 8 51 1 16 5 18 5 13 7 3 54 3 25 4 19 1 1 2 51 4 17 4 18 8 12 4 4 54.5 24.8 19.3 1.4 52.7 16.5 17.4 13.2 5 51.4 28.2 17.6 2.8 49.6 16.1 15.9 18.1 Pullets .5 . 56 7 18 5 20 9 3 9 48 3 16 1 21.7 13 9 1 47.3 20.7 27.1 4.9 46 7 14.5 20.0 18.8 1.5 55 8 19 9 21 2 3 1 49 9 17 2 17 7 15 2 2 56.0 20.4 22 1 6 52.6 15 4 16 8 15.2 3 67 1 12 6 19 6 7 58 8 12 17 12 2 4 70.4 8.8 20.5 .3 63.5 9.8 18.8 7.9 1931} GROWTH OF WHITE LEGHORN CHICKENS 115 TABLE 34. PERCENTAGE DISTRIBUTION OF ASH AND CALCIUM AMONG THE COM- POSITE SAMPLES ANALYZED IN WHITE LEGHORN CHICKENS OF DIFFERENT WEIGHTS AND SEX Approximate body weight Ash Calcium Flesh Bone Ofial Feathers Flesh Bone Offal Feathers Cockerels Ibs. .5. . perct. 15 4 perct. 59 2 perct. T> perct. 3 2 perct. 1 78 perct. 78 5 perct. 19 perct. 69 1 17.1 61 9 17 3 3 4 1 31 82 8 14 5 1 23 1.5 15 3 60 6 19 3 4 6 1 51 79 3 171 2 07 2 14 6 65 17 4 2 9 1 04 82 9 15 1 91 3 14.1 64 1 19 5 2 2 1 04 81 1 17 3 50 4 14 9 62 6 20 1 2 1 1 11 81 1 17 68 5 14.5 67.5 15.1 2.7 1^04 83.2 14^9 .87 Pullet I .5 16 6 60 9 19 3 3 1 86 81 4 16 1 57 1 17.4 60 4 18 7 3 3 1 47 80 5 17 1 90 1.5 15 5 62 "> 18 8 3 4 1 46 81 3 16 2 94 2 15 4 65 4 16 3 2 7 1 43 83 5 14 1 90 3 15.1 65 9 17 1 8 1 08 83 4 14 6 83 4 18.6 68.0 10.9 2.3 1.06 89.9 7.7 1.24 smaller proportion. However, from 62 to 68 percent of the ash and from 81 to 89 percent of the calcium in both cockerels and pullets were found in the bones of the dressed carcass. Total Digestible Nutrients in Birds of Different Ages and Sex. The total edible nutrients in White Leghorn chickens of different weights have been calculated and the results collected in Table 35. The outstanding feature of this table is the demonstration of the superiority of pullets at weights of 2 pounds or more in their content of edible dry matter, fat, and energy, unaccompanied by any inferi- TABLE 35. EDIBLE NUTRIENTS IN W T HITE LEGHORN COCKERELS AND PULLETS AT DIFFERENT WEIGHTS Approximate body weight , flesh Dr y Crude substance: protein Crude fat Ash Calcium Gross energy Cockerels Ibs. .5 gms. 92 gms. 27 4 gms. 19 4 gms. 4 1 gms. 1 2 gms. 04 cals. 145 1 199 49 7 42 4 5 6 2 8 .06 287 1.5.. 320 87 7 70 5 13 3 3 7 10 528 2 442 142 99 6 28 3 5 .11 781 3 686 204 152 43.5 7.3 .17 1 207 4 946 276 210 58 6 10 25 1 715 5 1 167 337 272 49.0 12.7 .28 2 Oil Pullets .5. . . 94 26 7 20 5 4.3 1.3 .04 158 1 209 52 8 46 5 4 2 8 .07 305 1.5 322 88 2 68.7 14.6 3.8 .10 524 2 465 143 98 1 32 9 5 .14 852 3 753 268 152 102.5 7.4 .17 1 769 4 1 027 451 171 249.7 10.3 .19 3 346 116 BULLETIN No. 367 [April, ority in the content of edible protein up to a body weight of 3 pounds. At the 4-pound weight the White Leghorn cockerel supplies about one-fourth more edible protein than the White Leghorn pullet. MATHEMATICAL ANALYSIS OF THE CHEMICAL DATA One of the main purposes of the chemical analysis of the birds slaughtered in this experiment was to secure data on the rate at which nutrients are deposited in the bodies of growing White Leghorn pullets 800 n 700 < 600 a U Z400 S300 O O O O OO O oOOOO CRUDE PROTEIN -COCKERELS ^^*-- jO ^ ^^ ^^ ,^ x^ "^^ ^: ^ X ^^'W=T53^l0.83t-.73IOt ^ -.0^854t 3 ^.0003355t 4 r--- ^f -^1 10 15 Z5 AGE IN WEEKS 30 35 FIG. 3. OBSERVED AND CALCULATED DRY SUBSTANCE AND CRUDE PROTEIN FOR WHITE LEGHORN COCKERELS and cockerels. These rates of deposition of nutrients are fundamental data in the exact estimation of the food requirements for growth of this species. There is, however, no good method of obtaining these rates of growth in terms of individual nutrients directly from the 1931} GROWTH OF WHITE LEGHORN CHICKENS 117 original data, since they were obtained from small groups of birds. The irregularity of these data, reflecting the operation of uncontrolled factors possessing no significance for the problem at hand, offers a ETHER EXTRACT-GRAMS SJ^ O* CD O ETHER EXTRACT -COCKERELS / , _ -> \ / / / / V / / / / A /, W'4.04-3.27t+.93l7t-j03599t 3 -.0003987t< 0^ / 4,000 23,000 UJ 1,000 10 15 20 25 AGE IN WEEKS JO 35 GROSS ENERGY- COCKER ELS 10 15 ZQ 25 AGE IN WEEKS 30 35 FIG. 4. OBSERVED AND CALCULATED ETHER EXTRACT AND GROSS ENERGY FOR WHITE LEGHORN COCKERELS serious obstacle to any simple and direct method of obtaining the desired information. This error, inherent in all biological investigations on growth, may be overcome by fitting to each group of data a mathematical equation 118 BULLETIN No. 367 [April, capable of describing them in a satisfactory manner. The closeness of description is, of course, measured by the deviations between the ob- served data and the estimations obtained from the fitted equation by 100 80 (0 < 60 a i "40 20 o, ASH-COCKERELS J> ^ ^ " X ~s* ,/ / / 2 / ^z / X W=.60+l.388 t .l659t 2 -.006537t J -'-.00007594t< ^ S* 10 15 20 AGE IN WEEKS 30 35 CALCIUM-GRAMS ro CM O O O O i CALCIUM-COCKERELS -e ^- ' ,-- * ^- ^ ^^ / >-" . -^" ^ W s .5|-.00ettl049t 2 -003796t 3 +0000400lt 4 10 15 20 AGE IN WEEKS zs 30 35 FIG. 5.- -OBSERVED AND CALCULATED ASH AND CALCIUM FOR WHITE LEGHORN COCKERELS solving for one of the variables, using properly assigned values of the other. Obviously such estimated values will show a regular variation of one variable on the other, capable of graphical description by a smooth curve. In performing this mathematical analysis, the fourth-degree equa- tion used for the age-body-weight data was used thruout. The age of 1931} GROWTH OF WHITE LEGHORN CHICKENS 119 each sample of birds submitted to chemical analysis, however, was determined by substituting in the growth equations (Nos. 2 and 3) the average body weight of the group (W) and solving for time (/). DRY SUBSTANCE-GRAMS ro .fe o> oo 0000 O ^> /^DRY SUBSTANCE-PULLETS / / ' / ^ W=IO.I+3.34t*l.906t 2 -.06884t ! t0006l50t 4 A 10 20 30 40 AGE IN WEEKS en 300 Z ex O zZOO o. iu 100 CRUDE PROTEIN-PULLETS W=8.69+8.768tn439t 2 -.06086t J +.00070a5t 10 20 30 40 AGE IN WEEKS FIG. 6. OBSERVED AND CALCULATED DRY SUBSTANCE AND CRUDE PROTEIN FOR WHITE LEGHORN PULLETS The fourth-degree equation was then fitted in turn to each set of data relating to the weights of each nutrient in successive groups of birds (Table 30), using as the time variable the estimated age of each group. The method of least squares was used thruout. The resulting equations were as follows: Cockerels Dry substance: W = -6.90 + 14.32* + 1.474* 2 - .06434/ 3 + .0008019* 4 (6) Protein: W = -.53 + 10.83* + .7310f - .02854* 3 + .0003355* 4 (7) Ether extract: W = 4.04 - 3.272* + .9317** - .03599** + .0003987** (8) 120 BULLETIN No. 367 [April, Gross energy: W = 45 + 46.37* + 9.7S5* 2 - .3641* 3 + .003969** (9) Ash: W = .60 + 1.388* + .1659* 2 - .006537* 3 + .00007594* 4 (10) Calcium: W = .51 - .002* + .1049* 2 - .003796* 3 + .00004001* 4 (11) Pullets Dry substance: W = 10.1 + 3.34* + 1.906* 2 - .06284*' + .0006150** (12) Protein: W = 8.69 + 2.768* + 1.439* 2 - .06086* 3 + .0007025** (13) Ether extract: W = -6.00 + 3.88* - .2373* 2 + .02500* 3 - .0004025** (14) Gross energy: W = 112 - 24.6* + 15.1 1* 2 - .4776* 3 + .004899* 4 (15) Ash: W = .45 + .867* + .1991* 2 - .008827* 3 + .0001031* 4 (16) Calcium: W = .42 + .037* + .08132* 2 - .003298* 3 + .00003747** (17) NOTE: In each case W is the weight in grams of the constituent and / is the age in weeks. 400 300 en Z oEOO 100 ETHER EXTRACT-PULLETS 10 ZO 30 40 AGE IN WEEKS / W 3 ll-24.6t-H5.llt*-.4776t 3 +.004899t< X 10 20 30 40 AGE IN WEEKS FIG. 7. OBSERVED AND CALCULATED ETHER EXTRACT AND GROSS ENERGY FOR WHITE LEGHORN PULLETS 1931] GROWTH OF WHITE LEGHORN CHICKENS 121 The closeness with which these equations fit the observed data is shown numerically in Table 36 and graphically in Figs. 3 to 8. Judging by eye only, the agreement between observed and calculated 60 50 40 20 10 ASH-PULLETS _- P ^ y ? / ^ / r 7 / / W=.45+867t*.l99lt 8 -.0088Z7t 3 *.OOOI03lt< L 10 80 30 40 AGE IN WEEKS 10 20 30 40 AGE IN WEEKS FIG. 8. OBSERVED AND CALCULATED ASH AND CALCIUM FOR WHITE LEGHORN PULLETS data is very good for ash, calcium, and crude protein, only fairly good for dry matter and gross energy, and rather poor for ether extract. A satisfactory estimation of the composition of newly hatched chicks was seldom possible by the use of these equations. Perhaps the most serious objection that may be used against these 122 BULLETIN No. 367 [April, w Ed a H U !5 PH O 8 w C/} x-^ gs as Q H J a u Q S5 Q W ? "3 B U 3 3 "3 U ^ a-'JS'S < * i/>-HOvf5Os ,-n- * rt a i T(HO OsOiWTf oo>or-ioio .-nt r~ ON >O <-i "5 -H tSCS . rt T(< t~ O> TjO <*< ff) \f> t~- O '*O>O'J < >O pjrt"NO OMO in -i CSCS CN^NOOMOSO *O\n TfOI^'HOOtN'OfO CNOr-oor- 00 >O Tj" r* 00 PO (N -H cs W * \o 00 t~r^^j< CNVO-H -H csrOTj-io 0*00 mTf^^pqr'l^vC o>-* i >O 00 00 sO >O -i r~ >O * W O "5 fS H c^ m ir> NO 00 t->O<3 O I * <* O t^ 00 (N O fO r~ ** 'f cs o oo TH rt OJf5tf) mfS 1 VO<^ 00 ->O rt \OOOt^ cs t^ ^H r^ O Ov -H^MTtl O> CS f5 -H r5 lO CM f5 W> O *C CS t^ f- 00 -H W vO -H * CN O 00 <-i -H csroro d r<) 10 s 00 O CM in * i^ "O ir> \Otn-O CO O O O r^. so O ^H to 'J' t^ ^ O> 00 tSl^ Ov * CM f; ID T}* m 1-1 m i. OvtT) (NrtOvCSOMO CSIOOOOOO & s O >-i cs Tf t^ o o* - ^H CS IO /) fO ^H CO o O * OMT) ^> (O Ov O* * CMrt O\ O\ O> O> CS iHescs-^t^ V3'* VO-H >O CNOO>W>O "H <-< cs cs * >o t^- -O 5 O OV-H ^ 00-*OsOO O O 00 10 O " ") cs * m t^ >o m "5 C*5 t^ OS CS t^ f*5 fO rtrt CS t5 Tj- 00 -H * IN 00 -H-H (NfO HOOr^oOu^t^OvvO t^'-^t^t^r^^^^Hf) tN^OOO Wlt^ H -~* ts ^mooovo^o CO ts >O >O O> vO H C4-*OOOf~ 1931} GROWTH OF WHITE LEGHORN CHICKENS 123 applications of a fourth-degree equation containing 5 constants to be evaluated from rather small groups of data is that the equation is too flexible, so that, for example, variations of the observed values at the higher ages have an undue effect upon the form of the curve. Thus, in Fig. 2, the fitted curve describing the growth in the body weights of the pullets attains a maximum at about 36 weeks, and then slowly TABLE 37. ESTIMATED CHEMICAL COMPOSITION AND ENERGY CONTENT OF WHITE LEGHORN CHICKENS AT EVEN WEIGHTS Body weight Age Dry substance Crude protein Ether extract Ash Calcium Gross energy Cockerels Ibs. .5 wks. 4 gms. 70 gms. 53 gms. 3 8 gms. 8 4 gms. 1 81 cats. 363 1 6 9 142 100 14 9 16 4 2 715 1.5 9 7 218 149 30 24 7 2 1 109 2 12 5 997 202 48 33 10 4 1 537 3 18.2 443 304 80 50 16 7 2 364 4 25 4 588 419 98 68 22 6 3 204 5 36.9 783 583 83 90 26.5 4 066 Pullets .5. . . 4 5 57 44 8 7 7 4 1 92 269 1. 8 2 133 97 21 7 16 4 4 5 682 1.5 11 5 216 151 38 25 7 3 1 189 2 14 9 304 202 62 33 9 9 1 749 3 22.4 489 286 141 47 14 4 2 988 4 44.9 814 381 329 61 19.8 6 153 bends downward, indicating a trend which larger groups of birds at these ages would not show. A similar objection applies to the curve for ether-extract content of cockerels (Fig. 4) . Under these conditions the equations given above cannot be used safely in predicting values much beyond the range of time observed, and in some cases predic- tions within this range approximating the highest observed age are probably not significant. Solving these equations for even weights, rather than for the actual average slaughter weights, gives the results summarized in Table 37, which results may be used in preference to those in Table 30 in predicting the average composition of White Leghorn chickens at even weights. The data in Table 37 may also be used to good advan- tage in computing the absolute and percentage composition of gains between even weights, and in computing the percentage composition of the birds at even weights. The results of this latter computation are contained in Table 38. The age of the 4-pound pullets could not be obtained from Equa- tion 3 for reasons already explained. For the purpose of obtaining such a prediction, Brody's curve of diminishing increments 2 * was 124 BULLETIN No. 367 [April, fitted to the growth data of pullets from 16 to 40 weeks of age. This equation, in its logarithmic form, is: log (1900 W) = 3.54345 .03586/. For weights of 2, 3, and 4 pounds, the ages are 15.4, 22.6, TABLE 38.- -ESTIMATED PERCENTAGE COMPOSITION AND ENERGY CONTENT OF WHITE LEGHORN CHICKENS AT EVEN WEIGHTS Body weight Dry substance Crude protein Ether extract Ash Calcium Gross energy per gram Cockerels Ibs. .5 perct. 30.9 perct. 23.2 perct. 1.7 percti 3.7 perct. .80 grn. cats. 1 600 1 31 3 22 3 3 3 5 93 1 576 1.5 32 21 9 4.5 3.6 1 05 1 630 2 32 7 22 2 5 3 3 6 1 15 1 694 3 . . 32 5 22 3 5 9 3 7 1 23 1 738 4 32 4 23 1 5 4 3.7 1 25 1 766 5 34.5 25.7 3.7 4.0 1.17 1 793 Pullets .5 25 3 19 5 3 8 3 2 85 1 187 1 29 3 21 4 4 8 3.6 1 00 1 504 1.5 31.8 22 2 5.6 3.7 1.07 1 747 2 33.5 22.3 6.8 3.7 1.10 1 928 3 36 21 10 4 3.4 1 06 2 196 4 44.9 21.0 18.1 3.3 1.09 3 391 and 44.9 weeks. The last value is used in the computations of the composition of 4-pound pullets contained in Tables 37 and 38. MINIMUM NUTRITIVE REQUIREMENTS OF WHITE LEGHORN CHICKENS FOR GROWTH By the differentiation of Equations 6 to 17 equations are obtained from which for each constituent the instantaneous rate of deposition fdW\ 77 I may be computed for any age (/). The rates obtained in this \ at / way from Equations 6 to 17 would be expressed in grams per week. Dividing by 7, the rates will be reduced to grams per day. These reduced differential equations are given below: DIFFERENTIAL EQUATIONS, SHOWING RATE OF GAIN PER DAY Cockerels Dry substance: -ft = 2.05 + .4213* - .02757* 2 + .0004582*' dW Protein: -^- = 1.55 + .2089* - .01223* 2 + .0001917*' dW Ether extract: -^ = -.47 + -2662* - .01542** + .0002278*' dW Gross energy: -^ = 6.6 + 2.787* - .1560* 2 + .002268*' dW Ash: dt .198 + .0474* - .002802* 2 + .00004339*' (18) (19) (20) (21) (22) 1931] GROWTH OF WHITE LEGHORN CHICKENS 125 dW Calcium: -^ = -.0003 -f- .02997* - .001627* 1 + .00002286*' (23) Pullets dW Dry substance: -^ = .48 + .545* - .02693* 2 + .00035 14*' (24) dW Protein: -^ = .40 + .41 It - .02608** + .0004014* 3 (25) dW Ether extract: ~^j = .55 - .0678* + .0107 If 4 - .0002300*' (26) dW Gross energy: ^ = -3.5 + 4.32* - .2047* 2 + .002800*' (27) dW Ash: -ft = .124 + -0569* - .003783* 2 + .0000589*' (28) dW Calcium: ~ d j = .005 + .0232* - .001413* 2 + .00002141** (29) Solving these differential equations for any age in weeks (/) will give the daily rate of depositions in grams of the constituents in ques- tion. The daily increments in chemical constituents and gross energy of White Leghorn chickens for ages at which body weights of .5, 1, 1.5, 2, 3, 4, and 5 pounds are attained, according to our own growth data, are summarized in Table 39. At a body weight of 2 pounds and an age of 12.5 weeks the cockerels were gaining in body weight at a rate of 11.8 grams per day, and were depositing in their bodies daily, on the average, 3.91 grams of dry matter, 2.63 grams of crude protein, .437 gram of ash, .165 gram of calcium and 21.5 calories of gross energy. The latter values represent the actual minimum need of nutrients by these birds for growth only, tho obviously they must be provided with larger amounts to allow for the food requirements of maintenance and activity, and for the wastage of food nutrients in digestion and metabolism. These additional factors in the food re- quirements of growing birds must be evaluated separately by methods other than those used in this study. The estimated requirements for growth of 2-pound pullets (14.8 weeks old) gaining at the slower rate of 9.6 grams daily are 3.78 grams of dry matter, 2.06 grams of protein, .328 gram of ash, .108 gram of calcium, and 24.8 calories of energy per day. The larger energy requirement of the pullet is an expression of its greater rate of fattening, represented at a weight of 2 pounds by a daily deposition of 1.15 grams of fat as compared with .90 gram in the cockerel of the same weight. For reasons already given, the estimated daily increments for the 5-pound cockerel and the 4-pound pullet cannot be accorded the same degree of accuracy as the estimates at the lower weights, within the range of experimental observation. The increments given in Table 39 126 BULLETIN No. 367 [April, TABLE 39. CALCULATED DAILY INCREMENTS IN CHEMICAL CONSTITUENTS AND GROSS ENERGY OF WHITE LEGHORN CHICKENS DURING GROWTH AT DIFFERENT BODY WEIGHTS Body weight Age Daily increments in ] jdy v ';ht Dry substance Crude protein Ether extract Ash Calcium Gross energy Cockerels Ibs. .5 wks. 4 01 ns. J 9 gms. 3 33 gms. 2 20 gms. 36 gms. 346 gms. 095 cats. 15 4 1 6.87 11 2 3 79 2 47 70 406 136 19 1.5 9.65 11.9 3 96 2 60 86 433 158 21 2 12 51 11 8 3 91 2 63 90 437 165 21 5 3 18 23 10 5 3 35 2 46 64 394 144 19 3 4 25.44 7 4 2 47 2 10 07 305 085 13 8 Si 33.04 5.0 2.40 2.01 -.28 .270 .038 10.2 Pullets .5 4 45 7 9 2 41 1 75 44 307 082 11 8 1 8 17 9 4 3 32 2 24 58 368 113 19 6 1.5 11.52 9.8 3 73 2 28 84 367 .117 23 4 2 14 85 9 6 3 78 2 06 1 15 328 108 24 8 3 22 38 7 2 3 13 1 04 1 81 162 056 22 1 42 38.35 1.59 .44 .73 .064 .024 19.0 'Calculations are for 2,136 grams, the weight of the last group of cockerels studied, rather than 2,268 grams (5 pounds even). Calculations are for 1,716 grams, the weight of the last group of pullets studied, rather than 1,814 grams (4 pounds even). TABLE 40. COMPARISON OF THE DAILY INCREMENTS DURING GROWTH IN PROTEIN, ASH, AND ENERGY FOR WHITE LEGHORN AND WHITE PLYMOUTH ROCK CHICKENS Body weight White Leghorns White Plymouth Rocks Protein Ash Energy Submaximal growth 1 Maximal growth 2 Protein Ash Energy Protein Ash Energy Cockerels Ibs. .5 gms. 2.20 gms. .346 cats. 15.4 gms. 1.42 gms. .23 cats. 10.5 gms. 1.57 gms. .26 cals. 11.6 1 2 47 .406 19 1.5 2.60 .433 21 1.88 .32 15.9 3.68 .63 31.1 2 2 63 437 21 5 2.5 2 39 43 22.5 6.21 1.11 58.5 3 2 46 394 19 3 3.5 2.65 .49 27.3 4.26 .79 43.9 4 2 10 305 13 8 4.5 2.34 .44 25.9 4.28 .81 47.5 5 2 01 270 10 2 5.5 1.28 .25 15.2 3.71 .72 43.9 Pullets .5 1 75 .307 11.8 1.24 .21 9.6 1.52 .26 11.8 1 2 24 368 19 6 1.5 2 28 367 23 4 1 69 .27 17.5 3.66 .59 37.9 2 2 06 328 24 8 2.5.. .. 2 06 .32 26.0 2.96 .45 37.4 3 1 04 162 22 1 3.5 1.56 .23 22.9 3.38 .49 49.5 4 44 064 19 4.5 2.70 .38 44.3 Estimates based on Illinois growth data; see 111. Agr. Exp. Sta. Bui. 278. "Estimates based on the more rapid growth of White Plymouth Rock chickens observed at the Purdue Station; see 111. Agr. Exp. Sta. Bui. 278. 1931] GROWTH OF WHITE LEGHORN CHICKENS 127 therefore refer to the ages and weights of the last groups of cockerels and pullets actually studied, i.e., 33.04 weeks and 2,136 grams for the cockerels, and 38.35 weeks and 1,716 grams for the pullets. These weights are slightly less than 5 pounds (2,268 grams) and 4 pounds (1,814 grams) respectively. The estimated daily increments in protein',' '-ash, and energy for White Leghorn chickens are smaller than those ol gained by a different method of mathematical analysis for the maxint ,m growth of White Plymouth Rock chickens as reported in Bulletin 278 of this Station. 10 * For the slower growth actually observed in the Illinois flock of birds, however, the rates are much closer. These comparisons are made in Table 40. The data contained in Tables 39 and 40, and the equations from which they have been obtained, are thus the most important data of the entire investigation. Their practical use in the formulation of scientific feeding standards must wait upon the satisfactory evalua- tion of maintenance requirements and requirements for muscular activity, and the satisfactory measurement of the wastage of food in digestion and metabolism. TENTATIVE FEEDING STANDARDS FOR GROWING WHITE LEGHORN AND WHITE PLYMOUTH ROCK CHICKENS In the absence of satisfactory evaluations and measurements it may be permissible, on the basis of available data and upon what may seem to be reasonable assumptions, to set up a tentative series of estimates of the nutritive requirements of growing White Leghorn and White Plymouth Rock chickens with reference to digestible crude protein, calcium,, and net energy. Protein Requirements. The requirements for protein relate to maintenance and growth. The preponderance of experimental evi- dence indicates that muscular activity does not, in the presence of adequate amounts of nonprotein nutrients, increase appreciably the breakdown of body protein or the need for food protein. This subject has been reviewed recently by Mitchell and Kruger 13 * and by Mitchell and Hamilton, 14 * so that the basis of the conclusion stated above need not be investigated here. The study reported in this bulletin and that relating to White Plymouth Rock birds reported in Bulletin 278 10 * afford information of the protein requirements for growth but not of those for mainten- ance. In estimating the maintenance requirements, the investigation of Ackerson, Blish, and Mussehl 1 * of the Nebraska Agricultural Ex- 128 BULLETIN No. 367 [April, periment Station on the endogenous metabolism of hens and capons has been consulted. In the publication describing this work, the ni- trogenous output of birds of different ages while subsisting upon a nitrogen-free diet is given. This wastage of body nitrogen may be considered as a measure of the minimum maintenance requirement for protein since, for the attainment of nitrogenous equilibrium, this wastage must be covered by dietary nitrogen supplied in practical nutrition by dietary protein. Data for birds younger than 5 to 6 months of age are not included ; for birds of these ages a rough extrap- olation of the curve for capons, upon which the most complete data were obtained, has been made. On this basis it has been assumed that at one month of age the daily endogenous loss of nitrogen is 375 mgms. per kilogram of body weight, and that this ratio decreases along an S-shaped curve (asshown on page 195 of the report* 1 ) . Altho it is possible that sex differences exist in this respect, the Nebraska data afford no basis for this assumption, and in a large number of similar experiments on rats at the Illinois Station no sex differences of this character have been observed. In the computations of the maintenance require- ments for protein given in Tables 42 and 43, therefore, the endogenous nitrogen per unit of body weight has been obtained by this approxi- mate method from the Nebraska data; multiplication by the body weight gives the total endogenous wastage per bird, and multiplica- tion of this value by the conventional factor of 6.25, the corresponding crude protein. These values are minimum values, and are of the same significance as the values for growth based upon the crude protein content of the daily gains. They may therefore be added together to give a total minimum protein requirement. The total protein requirements obtained in this way would repre- sent the requirements for digestible dietary protein only when the biological value of the dietary protein is equal to 100, indicating no wastage of digestible protein in the synthesis of body protein. But in practical nutrition the biological values of the proteins of feeds range from 50 to 85. Assuming a value of 50 as a safe average permits the statement of the minimum protein requirements in terms of di- gestible crude protein. The values in Tables 42 and 43 under this heading are therefore twice the minimum values contained in the column to the left. Calcium Requirements. For calcium, as for protein, the Illinois investigations provide information on growth requirements but not on maintenance requirements. Sherman's studies 16 * on the calcium re- quirement of man afford some basis for computing the calcium re- quirement of chickens from their maintenance requirement for pro- 1931] GROWTH OF WHITE LEGHORN CHICKENS 129 tein. According to Sherman, an adult man requires about 1 gram of calcium in maintenance for each 100 grams of digestible protein. But his protein requirement for maintenance upon which this ratio was based, i.e., 44 grams daily for an average man of 70 kilograms body weight, is probably about twice as high as the minimum requirement, as indicated, for example, by Hindhede's many investigations. In the Illinois investigations, digestible protein, for purposes of estimating nutrient requirements, has been assigned a biological value of 50, a conservative value to use in view of published results obtained at the Illinois Station. Hence it seems fair to assume that the calcium re- quirement is equal to 4 percent of the minimum crude protein re- quirement for maintenance, and for Tables 42 and 43 it has been so calculated. The sum of the calcium requirements for maintenance and growth is taken as the total calcium requirement since muscular activity is not known to affect the calcium metabolism. The total calcium requirements thus obtained are minimal in their significance; they allow for no wastage of calcium in either digestion or metabolism. With calcium supplements added to a calcium-poor ration, Forbes and his associates 6 * have obtained with growing pigs percentage retentions of calcium of 50 or better. If these values may be applied to poultry, the dietary calcium requirements may be taken as twice the minimum calcium requirements as given in the tables. The experiments on White Plymouth Rocks 10 * did not involve calcium analyses but only ash analyses. However, the analysis of White Leghorns shows that the calcium content of the total ash approximates rather closely to 30 percent. Hence the growth re- quirements of calcium for the former species were assumed to equal 30 percent of their ash requirements. Net Energy Requirements. The net energy requirements of growing birds may be factored into three components the require- ment for maintenance, the requirement for muscular activity, and the requirement for growth. Only the latter requirement is involved in the present study of White Leghorn chickens and n the study of White Plymouth Rocks reported in Bulletin 278. 10 * The basal heat production of chickens, however, has been the object of two experi- ments by Mitchell, Card, and Haines, 11 * reported in 1927. The basal metabolism of both White Leghorn and White Plymouth Rock chickens of different sex and ages was measured and expressed in calories per day per square meter of skin area exclusive of the area of the shanks and feet. In the calculations made for Tables 42 and 43, sex differences were not considered. Altho in the adult chicken (Rhode Island Red) the basal metabolism of pullets averages almost 130 BULLETIN No. 367 [April, . produced 1 I SSSS53SS3 Excess hea ~? oOoot-O>OoOt^r^ a o Isl ssss^sss <=! a o"o en T g.b .!> i>.5 g CN CN CN (N CN (N CN CN c c >, ^ CJ : oooacot-^xacoo 1? , : OOOt^OOOO P * e * Jlf i 5HS rt .Q'Sj | iO*nO^OOOO '^c_"3i 1 Tj-u^X'OO30'- ll C o :::::::: s 3 ^JO^^-^NCX; S"o gss "> mvOr-vo> Tj"OOWOOOO I'i 00 5 ^sssasss SS=S38 en H S ----""O CN S Id "3 U 2 1 V JM 00 -Si "9 d P O 1 U] g CJ 8 U -SS88S22 CNTfO X O 00000 *s OJ H 2 3 s 00 - > S"" S II ^tOCSNO^O * * CN NO VO 'ac c g I r - 00 ,_x_ '.=. 01 ^ > Q "3 ^ ^.n-O^r-^ oacsx-xx 1 = Q H 'S o h 0. <: S 01 o 3 - ^ cs m vo vO n O r- CN <> - t 'o c 1 U O S CN CN fS CN CN CN CN 00 -_.- "s ^ Id 2 g moiooxvo./) m O >n O X * 1 V n H "3 a 00 r* ~* CN CN r i S 'S ll minimi 1 n in ~m in '10 * * ' -; : H GROWTH OF WHITE LEGHORN CHICKENS 131 OWTH Equivalent weight of corn 00 S5SKSS O g 3 O W) ^^ O fC O* O (S O /5 O O* 3 s H a (N CSCN -H JNCSCJ 5 IS 1 X) ^2 CN oo f r- * tS 00 I-- Ov * r)< z H 1 u Activity I'SSJRSS 2S5RSR iTMOUTH R Mainte- nance |S3S= 5 (N<*5O>- O U OH | -2S3S55 2SSSSS H 00 O g S | . 00 Ov l5 * * T) Ul fS. o tf c3 O g 00 rf i v p U .? Ol'OO'l' 00 CS 2 oo --I-H cs 882S25 "o H z u s c BO 1 u _1) (NVO^VONOtS oysooorsrs .a _o' 3 ,0 5 Tj-Ot^mr^ oo vO 1 3 H a O H BO CS " >00t ~ 00 CN1010>01^10 V a 5 yst-cMWMt- int-0-*^^ 'o Q U BO riro WW5CS.H C H < ! iu c y in f, ir> ir> in -o U>10lOttO ireme g i 5 e 00 _,,, a s B Id J3 .- minimu I n * :::::: 2 \fnr>ir>\n\r.\n io>n>omio>n ^H cs f*^ ^ 1/5