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UNIVERSITY OF ILLINOIS 
 
 Agricultural Experiment Station 
 
 BULLETIN No. 278 
 
 THE GROWTH OF WHITE PLYMOUTH 
 ROCK CHICKENS 
 
 BY H. H. MITCHELL, L. E. CARD, 
 and T. S. HAMILTON 
 
 A significant indication of the probable future profitableness of 
 a flock of chickens is the way in which they grow. It is therefore 
 important to find out the form and quantity in which the essen- 
 tial nutrients must be supplied to support maximum growth. 
 
 URBANA, ILLINOIS, JUNE, 1926 
 
CONTENTS 
 
 INTRODUCTION 71 
 
 DESCRIPTION OF THE EXPERIMENT 73 
 
 EXPERIMENTAL RESULTS 75 
 
 Increase in Body Measurements with Age 77 
 
 Surface Area of the Birds at Different Ages 80 
 
 Relative and Absolute Growth of the Different Parts of the Carcass and 
 Viscera 87 
 
 Chemical Composition of the Birds at Different Weights 100 
 
 Rate of Retention of Nutrients During Growth 114 
 
 SUMMARY AND CONCLUSIONS 124 
 
 LITERATURE CITED 123 
 
 APPENDIX.. . 129 
 
THE GROWTH OF WHITE PLYMOUTH 
 ROCK CHICKENS 
 
 BY H. H. MITCHELL, L. E. GAUD, and T. S. HAMILTON" 
 
 The rate and manner in which a given species of animal grows, 
 besides being of great physiological importance, must form the basis 
 for any estimation of the nutrient requirements for that species. It is 
 also important that the practical animal husbandman know some- 
 thing of the normal growth of the animals which he is raising, in order 
 that he may judge the success of his own feeding operations. 
 
 The most scientific method of estimating the food requirements 
 of any species of animal for growth is undoubtedly the system devel- 
 oped by Armsby relative to the energy requirements. According to, 
 this system an estimate of the amount of energy that animals need at! 
 different stages of growth must be based upon reliable information 
 relating to three distinct points: first, the maintenance requirement of 
 the animals at different stages of growth; second, the normal rate of 
 increase in body weight during the growing period ; and third, the com- 
 position of the gains put on at different ages. Furthermore, in order i 
 to make practical use of this information in the formulation of feed- ' 
 ing standards for growth, it is necessary to know the extent of the util- 
 ization of food energy by growing animals at different ages. This 
 system has been developed by Armsby only in connection with energy 
 requirements and the energy values of feeds. There is every reason 
 to suppose, however, that the system could be extended to include other 
 nutrients such as protein and mineral matter, by obtaining for each 
 nutrient information analogous to that just indicated with reference 
 to energy. 
 
 The production of meat by growing animals is most commonly 
 measured simply by the increase in weight. However, the increase in). 
 weight at different ages is known to vary widely in composition. For 
 example, a pound of protoplasm such as a young animal would put on 
 during growth has an energy value of about 500 calories and a pro- 
 tein content of approximately 20 percent. As the age of the animal 
 increases, the water content of its gains decreases and the nature of 
 the solid matter changes progressively, due to an increasing proportion 
 of fat. In the last stages of fattening, a pound increase in weight may 
 have an energy value of 4,000 calories, and may contain only a mere 
 
 a H. H. MITCHELL, Chief in Animal Nutrition; L. E. CARD, Chief in Poultry 
 Husbandry; T. S. HAMILTON, Associate in Animal Nutrition. 
 
 71 
 
72 BULLETIN No. 278 [June, 
 
 trace of protein. It is quite evident that as this change in composi- 
 tion of gains takes place the food required to produce these gains will 
 increase in amount and change progressively in quality. 
 
 Among practical livestock men it may not be generally realized 
 that the composition of gains put on by meat animals varies as widely 
 as this. Even when it is realized that such differences do occur, little 
 practical use can be made of this knowledge since precise information 
 is not available regarding the composition of the gains which animals 
 put on at different ages. 
 
 In dairy production it is well known that the productive capacity 
 of a cow is measured not only by the amount of milk she will produce 
 but also by its composition. Since in this case the product can be so 
 readily removed from the animal and submitted to analysis, many 
 thousands of analyses of milk of different grades have been made with 
 various purposes in view, and have been reported in the literature of 
 the subject. At the present time any thorogoing feeding standard for 
 milk production considers not only the amount of milk produced but 
 also its composition, particularly in energy or total nutrients. Never- 
 theless, the need for . considering the composition of the product in 
 milk production is not so urgent as in meat production, because of the 
 narrower range in the composition of milk as compared with the com- 
 position of gains put on by growing and fattening animals. A pound 
 of milk testing 2.5 percent fat, for example, has an energy value of a 
 little over half that of a pound of milk testing 7 percent fat, while a 
 pound of gain put on by a young animal may have an energy value 
 of only one-eighth that of a pound of gain put on by an animal in the 
 last stages of fattening. 
 
 The most efficient method for determining the composition of the 
 gains of growing animals is to slaughter animals at different ages and 
 weights and submit their carcasses to a careful chemical examination. 
 From such data the composition of gains between two different weights 
 may be computed by assuming that the animals slaughtered at the 
 higher weight had the same composition at the lower weight as the 
 animals actually killed at that weight. While a considerable number 
 of analyses of the different farm animals at different ages and weights 
 may be found in the literature, the number is still insufficient in many 
 cases to form the basis of a reliable feeding standard. For example, 
 in arriving at his estimate of the energy requirements of growing pigs, 
 Armsby has sought for information concerning the energy content of 
 a pound increase in weight put on by pigs at birth and at an age when 
 growth may be assumed to have been practically complete. The 
 change in composition between these two ages is then assumed to vary 
 in a linear fashion with age. While the experimental information on 
 the composition of the early gains is fairly satisfactory, the informa- 
 tion relative to the energy value of gains put on at 18 to 24 months of 
 
THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 73 
 
 age consisted of determinations by Soxlet on two pigs 16.5 months of 
 age. One value was 1,401 calories per pound, the other was 2,485 
 calories per pound. Since the latter value was more consistent with 
 similar data on other animals, it was chosen in preference to the 
 former, but it is evident that much more complete information on this 
 point should be obtained. 
 
 No information is available in the literature from which the com- 
 position of gains put on by growing poultry may be computed. Very 
 little is known of the maintenance requirement of poultry or of the 
 difference in maintenance requirement between the different sexes. The 
 extent to which poultry utilize the energy of their feeds is also practic- 
 ally unknown, so that the formulation of a scientific estimate of the 
 food requirements of growing chickens is impossible at the present 
 time. The experiment reported in this bulletin is the first of a series 
 of investigations that is being undertaken by the Nutrition and Poul- 
 try Divisions of the Illinois Agricultural Experiment Station to obtain 
 information upon which feeding standards for poultry may be based. 
 
 DESCRIPTION OF THE EXPERIMENT 
 
 The object of the experiment reported in this bulletin was to in- 
 vestigate the growth of White Plymouth Rock chickens by measuring 
 the increase of size of the entire bird and of individual organs for 
 pullets, cockerels, and capons, and by determining the composition of 
 the gains in weight put on at different ages. 
 
 A flock of approximately 1,000 White Plymouth Rock chicks 
 hatched March 28, 1923, was used in this investigation. They were 
 range-reared on the colony house plan at the poultry farm, and were 
 fed the standard ration used at this Station for growing birds. Indi- 
 vidual weights of the birds were taken every two weeks. When the 
 flock reached an average weight of about 1.5 pounds, the cockerels and 
 pullets were separated and approximately half the cockerels were 
 caponized. From this time on they were fed in three groups pullets, 
 cockerels, and capons. 
 
 Groups of birds were removed according to weight rather than 
 age, for measurement, slaughter, and analysis. Five chicks were se- 
 lected from the entire flock at weights of .5 pound, 1 pound, and 1.5 
 pounds, these selections including only cockerels in so far as the sex 
 could be distinguished. To determine whether the measurements and 
 composition of the birds were greatly affected by age, when killed at 
 the same weight, two groups of 5 chicks each, differing by two weeks 
 in age, were slaughtered at the 1 -pound weight. 
 
 At the 2-pound weight two groups of 5 birds each were selected 
 for slaughter, one consisting of 5 pullets and the other of 5 cockerels. 
 
74 BULLETIN No. 273 [June, 
 
 s 
 
 From this weight on, the selections of birds were made at intervals of 
 1 pound. Starting with a weight of 3 pounds, 5 pullets, 5 cockerels, 
 and 5 capons were selected for measurement and slaughter. At 1- 
 pound intervals thereafter the growth of pullets was studied up to a 
 weight of 5 pounds, and the growth of cockerels and capons up to a 
 weight of 7 pounds. 
 
 The following measurements were made on 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 tip of beak 
 
 4. Length from rump to shoulder 
 
 5. Circumference of trunk just behind wings 
 
 6. Length of shank 
 
 7. Length of middle toe 
 
 8. Length of drumstick 
 
 9. Length of keel bone 
 
 10. Breadth from hip to hip 
 
 The birds were then killed, bled, and dry picked. The skins were 
 removed and their areas determined. The carcasses were then cut 
 up and fresh weights of the following portions were taken: 
 
 1. Blood 13. Pancreas 
 
 2. Feathers 14. Spleen 
 
 3. Head 15. Lungs 
 
 4. Shanks and feet 16. Testicles (in cockerels) 
 
 5. Skin 17. Gullet and proventriculus 
 r} ' 6. Neck 18. Gizzard 
 
 7. Legs above hock 19. Intestinal tract 
 
 8. Wings 20. Contents of gizzard 
 
 9. Torso 21. Contents of intestinal tract 
 
 10. Heart 22. Total bones in dressed carcass 
 
 11. Liver 23. Total flesh in dressed carcass 
 
 12. Kidneys' 
 
 The length of the intestinal tract in each bird was also measured. 
 
 For each group of 5 birds the following three composite samples 
 were made up for analysis: 
 
 1. All bones, except those in head, shanks, and feet 
 
 2. Flesh, heart, liver, and gizzard 
 
 3. Offal, including the blood, feathers, head, shanks and feet, skin, and all 
 viscera not included in the second sample 
 
 Each of these three samples was ground fresh, preserved with exactly 
 1 percent of thymol (a correction for which was made in reporting the 
 analyses), and analyzed in a fresh condition for moisture, nitrogen, 
 ether extract, and ash. The gross energy of each sample was directly 
 determined in the bomb calorimeter. 
 
 'The kidneys were not weighed in the .5-pound chicks. 
 
1926'] THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 EXPERIMENTAL RESULTS 
 
 73 
 
 The flock of White Plymouth Rock chickens from which birds 
 were taken for measurement and analysis was weighed at bi-weekly 
 intervals. The weights thus obtained are compiled in Table 1. The 
 weight of 46 grams given as the hatching weight of the chicks is actu- 
 ally the weight of the chicks at two days of age. The birds were ob- 
 tained from a commercial hatchery and were weighed immediately 
 
 TABLE 1. BIWEEKLY WEIGHTS OF THE WHITE PLYMOUTH ROCK CHICKENS 
 USED IN THIS STUDY 
 
 Age 
 
 Cockerels 
 
 Pullets 
 
 Capons 
 
 Number 
 of 
 birds 
 
 Aver- 
 age 
 weight 
 
 Biweekly 
 increase 
 in weight 
 
 Number 
 of 
 birds 
 
 Aver- 
 age 
 weight 
 
 Biweekly 
 increase 
 in weight 
 
 Number 
 of 
 birds 
 
 Aver- 
 age 
 weight 
 
 Biweekly 
 increase 
 in weight 
 
 wks. 
 
 
 gms. 
 
 gms. 
 
 
 gms. 
 
 gms. 
 
 
 gms. 
 
 gms. 
 
 
 
 
 46 
 
 
 
 46 
 
 
 
 
 
 ?, 
 
 400 
 
 87 
 
 41 
 
 507 
 
 85 
 
 39 
 
 
 
 
 4 
 
 401 
 
 178 
 
 91 
 
 502 
 
 163 
 
 78 
 
 
 
 
 6 
 
 401 
 
 308 
 
 130 
 
 493 
 
 280 
 
 117 
 
 
 
 
 8 
 
 399 
 
 477 
 
 169 
 
 472 
 
 416 
 
 136 
 
 
 
 
 10 
 
 391 a 
 
 605 
 
 128 
 
 420 
 
 535 
 
 119 
 
 
 
 
 12 
 
 184 
 
 716 
 
 111 
 
 384 
 
 602 
 
 67 
 
 150 
 
 675 
 
 70 
 
 14 
 
 178 
 
 907 
 
 191 
 
 363 
 
 752 
 
 150 
 
 135 
 
 892 
 
 217 
 
 16 
 
 170 
 
 1 150 
 
 243 
 
 353 
 
 919 
 
 167 
 
 139 
 
 1 095 
 
 210 
 
 18 
 
 163 
 
 1 229 
 
 79 
 
 322 
 
 1 036 
 
 117 
 
 129 
 
 1 271 
 
 176 
 
 20 
 
 152 
 
 1 347 
 
 118 
 
 312 
 
 1 140 
 
 104 
 
 129 
 
 1 379 
 
 108 
 
 22 
 
 145 
 
 1 557 
 
 210 
 
 293 
 
 1 285 
 
 145 
 
 119 
 
 1 658 
 
 279 
 
 24 
 
 135 
 
 1 636 
 
 79 
 
 281 
 
 1 403 
 
 118 
 
 108 
 
 1 849 
 
 191 
 
 26 
 
 118 
 
 1 756 
 
 120 
 
 267 
 
 1 533 
 
 130 
 
 113 
 
 1 899 
 
 50 
 
 28 
 
 116 
 
 1 962 
 
 206 
 
 247 
 
 1 647 
 
 114 
 
 74 
 
 2 206 
 
 307 
 
 30 
 
 112 
 
 2 135 
 
 173 
 
 230 
 
 1 734 
 
 89 
 
 77 
 
 2 330 
 
 124 
 
 32 
 
 116 
 
 2 062 
 
 -73 
 
 223 
 
 1 774 
 
 40 
 
 74 
 
 2 371 
 
 41 
 
 34 
 
 93 
 
 2 515 
 
 453 
 
 200 
 
 2 025 
 
 251 
 
 67 
 
 2 449 
 
 78 
 
 36 
 
 69 
 
 2 536 
 
 21 
 
 186 
 
 2 005 
 
 -20 
 
 43 
 
 2 385 
 
 -64 
 
 38 
 
 70 
 
 2 623 
 
 87 
 
 
 
 
 39 
 
 2 497 
 
 112 
 
 40 
 
 67 
 
 2 798 
 
 175 
 
 
 
 
 39 
 
 2 587 
 
 90 
 
 4?, 
 
 64 
 
 2 744 
 
 -54 
 
 
 
 
 42 
 
 2 516 
 
 -71 
 
 44 
 
 62 
 
 2 804 
 
 60 
 
 
 
 
 37 
 
 2 679 
 
 163 
 
 46 
 
 46 
 
 2 778 
 
 -26 
 
 
 
 
 29 
 
 2 759 
 
 80 
 
 "Approximately half the cockerels were caponized at this time. 
 
 on arrival at Urbana. The decrease in numbers of birds indicated in 
 the table was due not only to mortality, but also to the fact that birds 
 were removed from this flock at various times for purposes other than 
 those of this experiment. 
 
 A comparison of the growth rate of these White Plymouth Rock 
 chickens with that recorded by Philips 2 shows that the growth obtained 
 in this experiment was considerably slower and less sustained than that 
 obtained at Purdue. In addition to the fact that these chicks appear 
 to have come from a rather small strain of White Plymouth Rocks, it 
 
76 
 
 BULLETIN No. 278 
 
 [June, 
 
 G 
 
 o 5 
 UCQ 
 
 
 
 PH 
 
 w 
 
 pj 53 
 
 a 
 
 o 
 
 CQ 
 
 H 
 
 O 
 
 H 
 
 Approximate slaughte 
 weigh 
 
 "* CO 
 (N "3 
 CO (N 
 
 OCO 
 
 55 
 N 
 
 *.-. 
 
 i-H i-( ^H COIN 
 
 ~H CO 
 
 r^t^ 
 
 o 
 
 1> 
 
 CO-* 
 
 : 
 
 -S 
 
 i-i ^J 
 
 1 
 
 s 
 
 3 bO 
 
 HHTHiftsl "^ 
 
 % i <t_i 
 
 o 
 
 e o .. . 
 1-0 
 &b g^ 
 
 .2 
 
 3 1 
 
 u 
 
THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 77 
 
 should be pointed out that the environment under which they were 
 reared was not ideal. The range area in use contained no natural 
 shade and artificial straw shelters had to be constructed. The lack of 
 shade probably was partly responsible for the rather slow rate of 
 growth obtained. 
 
 From two weeks of age on the cockerels increased in weight at a 
 more rapid rate than the pullets (Table 1). No clear difference in 
 growth is apparent between cockerels and capons, except for a slightly 
 more rapid growth of the capons from the 18th to the 32d week. 
 
 The biweekly increases in weight exhibit what might be called a 
 cyclic tendency, it will be noted from Table 1. The authors hesitate 
 to attach much significance to these cycles. While there is a tendency 
 to interpret such changes in the rate of growth as indicating "cycles of 
 growth," such an interpretation fails to consider important environ- 
 mental factors. The weather, particularly, may exhibit periodic var- 
 iations and these very probably exert a pronounced effect on the 
 growth of the animals. The discussion of this point will be resumed in 
 a later section of the bulletin. 
 
 INCREASE IN BODY MEASUREMENTS WITH AGE 
 
 The average body measurements of the several groups of birds re- 
 moved at different weights are given in Tables 2, 3, and 4. These 
 
 TABLE 3. AVERAGE BODY MEASUREMENTS OF WHITE PLYMOUTH ROCK PULLETS 
 
 AT DIFFERENT WEIGHTS: EACH FIGURE Is AN AVERAGE OF FIVE BIRDS 
 
 (All measurements are in centimeters) 
 
 Approximate slaughter weight 
 
 2 
 
 3 
 
 4 
 
 5 
 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Age in days 
 
 73 
 
 94 
 
 189 
 
 219 
 
 Live weight in grams 
 
 961 
 
 1 342 
 
 1 842 
 
 2 340 
 
 Depth at front end of keel 
 
 9 3 
 
 10 7 
 
 11 6 
 
 12 4 
 
 Depth at rear end of keel 
 
 9 
 
 10 1 
 
 11 1 
 
 12 5 
 
 Length of keel 
 
 8.9 
 
 10.3 
 
 11.9 
 
 12.7 
 
 Length of drumstick 
 
 13.0 
 
 15.0 
 
 15.2 
 
 15.8 
 
 Length of shank 
 
 10.0 
 
 11.1 
 
 10.9 
 
 11.6 
 
 Length of middle toe 
 
 7.0 
 
 7.5 
 
 7.1 
 
 7.6 
 
 Rump to shoulder 
 
 16.2 
 
 18.0 
 
 18.8 
 
 19.5 
 
 Length over all 
 
 35.0 
 
 39.0 
 
 40.0 
 
 41.0 
 
 Mid-circumference 
 
 25.0 
 
 29.0 
 
 33.0 
 
 36.0 
 
 Breath at hips 
 
 6.4 
 
 7.8 
 
 8.1 
 
 8.9 
 
 tables also include the average live weight in grams and the age in 
 days. Each group of birds includes 5 individuals, except the group 
 removed at approximately 1 pound in weight, which includes two lots 
 of birds measured at dates two weeks apart. The measurements for 
 
78 
 
 BULLETIN No. 278 
 
 [June, 
 
 these two lots at the same weight were so nearly the same that they 
 have been averaged together.* 
 
 The change in size of the birds as indicated by these measure- 
 ments may be studied to best advantage probably by expressing the 
 average measurements at increasing weights in percentage of the cor- 
 responding measurement of the .5-pound chicks. This has been done 
 for the cockerels as shown in Table 5, which also includes values re- 
 lating to body surface. Practically all of the measurements taken on 
 these birds increased in approximately the same proportion when re- 
 ferred to the measurements of the .5-pound chicks. Thus, for all of 
 the measurements except the length of middle toe the 7-pound cock- 
 
 TABLE 4. AVERAGE BODY MEASUREMENTS OP WHITE PLYMOUTH ROCK CAPONS 
 
 AT DIFFERENT WEIGHTS: EACH FIGURE Is AN AVERAGE OF FIVE BIRDS 
 
 (All measurements are in centimeters) 
 
 Approximate slaughter weight 
 
 3 
 Ibs. 
 
 4 
 Ibs. 
 
 5 
 Ibs. 
 
 6 
 Ibs. 
 
 7 
 Ibs. 
 
 Age in davs 
 
 88 
 
 170 
 
 180 
 
 215 
 
 240 
 
 Live weight in grams 
 
 1 375 
 
 1 702 
 
 2 285 
 
 2 684 
 
 3 188 
 
 Depth at front end of keel 
 
 11.0 
 
 12 3 
 
 13.2 
 
 13.2 
 
 13.4 
 
 Depth at rear end of keel 
 
 10 2 
 
 10 8 
 
 12 3 
 
 12 2 
 
 13 4 
 
 Length of keel 
 
 9 7 
 
 11 1 
 
 12 1 
 
 13 
 
 13 5 
 
 Length of drumstick 
 
 15 3 
 
 17 1 
 
 18 4 
 
 18 5 
 
 18 2 
 
 Length of shank 
 
 11 7 
 
 12 6 
 
 13 8 
 
 13 5 
 
 13 4 
 
 Length of middle toe 
 
 7 9 
 
 8 
 
 8 7 
 
 8 4 
 
 8 7 
 
 Rump to shoulder 
 
 17 8 
 
 19 8 
 
 20 6 
 
 22 2 
 
 21 9 
 
 Length over all 
 
 39 
 
 45 
 
 44 
 
 47 
 
 46 
 
 Mid-circumference 
 
 29 
 
 30 
 
 35 
 
 37 
 
 40.0 
 
 Breadth at hips 
 
 7.8 
 
 8.4 
 
 8.7 
 
 9.4 
 
 9.8 
 
 erels were approximately 2.5 times as large as the .5-pound. This can 
 be interpreted to mean that the conformation of the birds did not 
 change materially during the whole course of growth from .5 pound to 
 7 pounds in weight. The body weight itself, of course, increased much 
 more rapidly when computed in this way than did the body measure- 
 ments, while the body surface, as would be expected, increased much 
 
 The average measurements of these two groups of birds removed at a 
 weight of approximately 1 pound, but at an interval of two weeks, were as fol- 
 lows: 
 
 (Body measurements in centimeters) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 o 
 
 
 o 
 
 
 
 o 
 
 
 O u 
 
 Age 
 
 days 
 
 
 xj 6 
 
 j= 
 a. c 
 
 V O 
 
 at. 
 
 V 
 
 j: 
 
 to 
 
 c"o 
 
 *i 
 
 j- 3 
 
 M 
 
 fs 
 
 MT3 
 C"O 
 
 S a 
 
 3 a 
 
 c 
 
 s = 
 
 " w 
 0/0 
 
 e s 
 
 3 O 
 
 
 nk S 
 
 B 2 ? 
 
 Qi 
 
 fig 
 
 J J* 
 
 nJ-5 
 
 i-)"S 
 
 hJ E 
 
 
 
 
 Uii 
 
 -S 
 
 43... 
 
 446 
 
 518 
 
 7 
 
 7.5 
 
 6 7 
 
 9 1 
 
 6 9 
 
 5 5 
 
 5 2 
 
 25 1 
 
 19 1 
 
 11 8 
 
 57 
 
 452 
 
 511 
 
 7.1 
 
 7.5 
 
 6.8 
 
 9.4 
 
 6.9 
 
 5.6 
 
 5.2 
 
 25.7 
 
 19.4 
 
 11.9 
 
THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 79 
 
 less rapidly than did the body weight. The increase in size of the pul- 
 lets and capons may be studied by a slightly different method, as ex- 
 emplified in Tables 6 and 7. In these tables the body measurements 
 of pullets and capons of different weights have been expressed as per- 
 centages of the corresponding measurements of cockerels of the same 
 weight. In this way, differences in the conformation of these two 
 groups of birds as compared to the cockerels have been brought out. 
 
 TABLE 5. RELATIVE INCREASE IN BODY WEIGHT, BODY SURFACE, AND BODY 
 MEASUREMENTS OF WHITE PLYMOUTH ROCK COCKERELS DURING GROWTH 
 
 Approximate slaughter 
 weight 
 
 0.5 
 Ib. 
 
 1 
 Ih 
 
 1.5 
 Ibs. 
 
 2 
 Ibs. 
 
 3 
 Ibs. 
 
 4 
 Ibs. 
 
 5 
 
 Ibs. 
 
 6 
 .Ibs. 
 
 7 
 Ibs. 
 
 
 
 
 
 
 
 
 
 
 
 BODY WEIGHT 
 
 100 
 
 194 
 
 290 
 
 428 
 
 587 
 
 769 
 
 964 
 
 1 113 
 
 1 402 
 
 BODY SURFACE 
 
 100 
 
 193 
 
 279 
 
 369 
 
 452 
 
 549 
 
 659 
 
 731 
 
 814 
 
 BODY MEASUREMENTS 
 Depth at front end of 
 keel 
 
 100 
 
 132 
 
 160 
 
 183 
 
 206 
 
 236 
 
 247 
 
 253 
 
 257 
 
 Depth at rear end of 
 keel 
 
 100 
 
 136 
 
 158 
 
 165 
 
 191 
 
 204 
 
 213 
 
 229 
 
 251 
 
 Length of keel 
 
 100 
 
 134 
 
 160 
 
 186 
 
 206 
 
 234 
 
 244 
 
 262 
 
 278 
 
 Length of drumstick . . . 
 Length of shank 
 
 100 
 100 
 
 131 
 130 
 
 160 
 158 
 
 194 
 200 
 
 217 
 215 
 
 250 
 245 
 
 263 
 260 
 
 261 
 257 
 
 263 
 257 
 
 Length of middle toe. . 
 Rump to shoulder 
 Length over all 
 
 100 
 100 
 100 
 
 125 
 130 
 130 
 
 145 
 152 
 148 
 
 177 
 184 
 184 
 
 184 
 201 
 204 
 
 186 
 218 
 224 
 
 205 
 236 
 230 
 
 193 
 240 
 245 
 
 205 
 242 
 246 
 
 Mid-circumference. . . . 
 Breadth at hips 
 
 100 
 100 
 
 134 
 127 
 
 150 
 141 
 
 179 
 163 
 
 203 
 183 
 
 224 
 215 
 
 245 
 222 
 
 259 
 234 
 
 266 
 256 
 
 TABLE 6. AVERAGE BODY MEASUREMENTS OF WHITE PLYMOUTH ROCK PULLETS AT 
 
 DIFFERENT WEIGHTS, EXPRESSED AS PERCENTAGES OF THE CORRESPONDING 
 
 MEASUREMENTS OF COCKERELS 
 
 Approximate slaughter weight 
 
 2 
 
 3 
 
 4 
 
 5 
 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 IDS. 
 
 Age in days 
 
 73 
 
 94 
 
 189 
 
 219 
 
 Live weight in grams 
 
 961 
 
 1 342 
 
 1 842 
 
 2 340 
 
 Depth at front end of keel 
 
 96 
 
 98 
 
 93 
 
 95 
 
 Depth at. rear end of keel 
 
 99 
 
 96 
 
 99 
 
 107 
 
 Length of keel 
 
 97 
 
 100 
 
 102 
 
 104 
 
 Length of drumstick 
 
 96 
 
 99 
 
 87 
 
 86 
 
 Length of shank 
 
 94 
 
 97 
 
 84 
 
 84 
 
 Length of middle toe 
 
 90 
 
 93 
 
 87 
 
 84 
 
 Rump to shoulder 
 
 97 
 
 98 
 
 95 
 
 91 
 
 Mid-circumference 
 
 98 
 
 97 
 
 91 
 
 91 
 
 Breadth at hips 
 
 96 
 
 104 
 
 92 
 
 98 
 
 The pullets at any weight were, in general, smaller in external 
 measurement than the cockerels of like weight (Table 6). The only 
 measurement remaining approximately the same in the two sexes is 
 
80 
 
 BULLETIN No. 278 
 
 [June, 
 
 the length of keel. The leg measurements of the pullets in particular 
 were appreciably smaller than those of the cockerels, especially after 
 the weight of 3 pounds was reached. 
 
 A similar comparison of capons and cockerels is made in Table 7. 
 Altho most of the measurements on the capons were slightly less than 
 the corresponding measurements on cockerels of similar weight, no 
 very distinct differences are evident. Castration does not appreciably 
 affect the body conformation of White Plymouth Rock chickens. 
 
 TABLE 7. AVERAGE BODY MEASUREMENTS OP WHITE PLYMOUTH ROCK CAPONS AT 
 
 DIFFERENT WEIGHTS, EXPRESSED AS PERCENTAGES OF THE CORRESPONDING 
 
 MEASUREMENTS OF COCKERELS 
 
 Approximate slaughter weight 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 
 IDS. 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Age in days 
 
 88 
 
 170 
 
 180 
 
 215 
 
 240 
 
 Live weight in grams 
 
 1 375 
 
 1 702 
 
 2 285 
 
 2 684 
 
 3 188 
 
 Depth at front end of keel 
 
 101 
 
 98 
 
 101 
 
 99 
 
 99 
 
 Depth at rear end of keel 
 
 97 
 
 96 
 
 105 
 
 97 
 
 97 
 
 Length of keel 
 
 94 
 
 95 
 
 99 
 
 99 
 
 97 
 
 Length of drumstick 
 
 101 
 
 98 
 
 100 
 
 101 
 
 99 
 
 Length of shank 
 
 103 
 
 97 
 
 100 
 
 99 
 
 99 
 
 Length of middle toe 
 
 98 
 
 98 
 
 97 
 
 99 
 
 97 
 
 Rump to shoulder 
 
 97 
 
 100 
 
 96 
 
 102 
 
 100 
 
 Length over all 
 
 97 
 
 102 
 
 98 
 
 98 
 
 98 
 
 Mid-circumference 
 
 100 
 
 94 
 
 100 
 
 100 
 
 105 
 
 Breadth at hips 
 
 104 
 
 95 
 
 96 
 
 98 
 
 93 
 
 SURFACE AREA OF THE BIRDS AT DIFFERENT AGES 
 
 One of the objects of this investigation was to determine the sur- 
 face area of the birds at different ages and weights, for the purpose of 
 deriving a formula by which the area of a bird may be computed from 
 certain measurements that can be taken readily on the live bird. The 
 idea in mind was to use such a formula in later work in determining 
 the intensity of the basal heat production per unit of body surface. 
 Therefore, after the birds were killed and picked, the skin was re- 
 moved and cut up into sections that would flatten out evenly. The 
 sections were then stretched on paper, pinned down, and outlined in 
 pencil. It was very soon found that the skins were quite elastic, so 
 that the tension of the stretched skin could be varied considerably. In 
 all of this work, therefore, the skins were stretched about as much as 
 possible, and in order to determine the error resulting from differences 
 in the tension applied, each skin was stretched independently by two 
 men and thus outlined twice. The area of each outline was then 
 measured with a planimeter. 
 
 The average results of these determinations are given in Table 8. 
 There is also included, for each group of 5 birds, the average percent- 
 
1926] 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 81 
 
 G m 
 
 as 
 
 tc 
 
 z 
 
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 M a3 
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 g I 
 
 ^ 
 
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 i 
 
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 i : 
 
 
 
 
 
 
 
 o ai.2 
 
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 imate slaughter weight 
 
 KBI6 
 
 age skin area 
 age percentage differe 
 een duplicate determin 
 
 rs 
 age skin area 
 age percentage differe 
 een duplicate determin 
 
 I 
 
 age skin area 
 age percentage differ 
 een duplicate determin 
 
 1 
 
 o 
 
 8 
 
 9 
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 \ 
 
 8 
 
 w v* || * 
 
 ||* 
 
 t 
 
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 a 
 
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 O PL. 
 
 O 
 
 
82 BULLETIN No. 278 \_June. 
 
 age difference between duplicate determinations. It is evident that 
 the error in this direct determination of skin area is considerable and 
 varies widely. It also appears that, except for the 4-pound birds, the 
 skin area of cockerels, pullets, and capons of similar weight was quite 
 similar. At least no constant differences between the three groups of 
 birds are revealed. 
 
 The first attempt to estimate the skin area of the cockerels, for 
 which the most complete series of determinations w r as available, is 
 shown in Table 9. Since the Meeh formula is the simplest formula 
 relating surface to weight, and hence the most practicable when a 
 reasonable degree of accuracy can be realized by its use, it was ap- 
 plied first to the nine groups of cockerels. The average value for k 
 from these nine average determinations was 9.55. A comparison of the 
 actual skin areas with the estimated skin areas, using the formula 
 S = 9.55 W % , is given in the upper part of the table. The formula 
 evidently gives a very poor determination for the .5-pound chicks, and 
 an indifferent determination for the 1-, 5-, and 6-pound birds. 
 
 If the .5-pound chicks are disregarded in the determination of the 
 Meeh constant, the average value of this constant becomes 9.85 in- 
 stead of 9.55. Using the latter constant in estimating the skin area of 
 the last eight groups of birds, the values given in the low r er half of 
 Table 9 are obtained. While the estimated areas for the 5- and 6- 
 pound birds are less in error than the estimates by the other formula, 
 the. estimate for the 1-pound chicks is considerably less accurate. 
 However, the Meeh formula can be considered to apply with consid- 
 erable accuracy to birds weighing more than 1 pound, and if the con- 
 stant were still further raised, even a better fit would be obtained 
 above this weight. The success of the Meeh formula as applied to 
 the estimation of the surface area of White Plymouth Rock chicks is 
 to be expected from the fact illustrated in Table 5 that the conforma- 
 tion of this breed of birds is not greatly affected by size. 
 
 In attempting to improve the Meeh formula for chickens, the 
 successful experience of investigators, w r orking with other animals, in 
 introducing a linear body measurement into the formula, was con- 
 sidered. The measurement most frequently used with the weight in 
 defining the conformation of an animal is a measurement relating to 
 the body length. Thus, Du Bois' formula for computing the surface 
 area of human beings introduces the height measurement, while the 
 formulas of Hogan and Skouby 3 for the determination of the surface 
 area of cattle and swine introduce a body length formula, that is, the 
 length from the point of the withers to the end of the ischium, or to 
 the root of the tail. The corresponding measurement on a chicken 
 might be taken as the total body length from beak to rump. But in 
 the experience of the authors, this length is difficult to take accurately, 
 
1926] 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 83 
 
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 PH U 
 
84 BULLETIN No. 278 [June, 
 
 because the distance obtained depends so much on the tension used in 
 stretching out the bird. An alternative measurement which could be 
 obtained with great accuracy was the shoulder-to-rump measurement. 
 However, a formula involving both weight and rump-to-shoulder dis- 
 tance that would apply satisfactorily to all nine groups of cockerels 
 could not be found, the error in estimating the area of the .5-pound 
 chicks being almost as great as that resulting from the application of 
 the Meeh formula. If the .5-pound chicks are disregarded, however, 
 the following formula is found to apply satisfactorily to the heavier 
 cockerels: S = 5.86 W- 5 L- G , in which S is the area in square centime- 
 ters, W the body weight in grams, and L the rump-to-shoulder meas- 
 urement in centimeters. 
 
 The estimates made by this formula of the area of the remaining 
 eight groups of cockerels are given in the upper section of Table 10. 
 While this formula gives a better estimate of surface area in these 
 classes than the Meeh formula, the estimate for the 1 -pound birds is 
 still appreciably higher than the actual area. 
 
 Using the same formula with the same constant in estimating the 
 area of the pullets and capons, satisfactory results were obtained with 
 the exception of the 4-pound birds in each of the groups. For some 
 reason, at present unknown, the observed areas of the 4-pound capons, 
 and to a less extent of the 4-pound pullets, were considerably higher 
 than the areas of the 4-pound cockerels, and were so much greater 
 than the observed areas for the 3-pound pullets and capons that they 
 may be considered as exceptional values, not representative of birds of 
 this size. Since there seemed to be no hope of devising a formula that 
 would take care of these exceptional values any better than the one 
 given above, no further attempt was made to improve upon it. 
 
 In attempting to see whether the weight-body-length formula 
 given above for White Plymouth Rock chickens would apply to other 
 breeds of chickens, the weight, the distance from rump to shoulder, 
 and the skin areas of 5 Rhode Island Red hens and of 5 Single Comb 
 White Leghorn hens were determined. The area was then estimated 
 by means of the formula derived from White Plymouth Rock meas- 
 urements. The results of this test are given in Table 11, from which 
 it is evident that the areas of the Rhode Island Red hens could be 
 estimated with considerable accuracy with this formula, probably just 
 as accurately as they could be measured directly by skinning the birds. 
 For the White Leghorn hens, however, the estimate was always con- 
 siderably in excess of the actual area. However, by reducing the con- 
 stant from 5.86 to 5.03, the resulting estimates of skin area were sat- 
 isfactory. The conformation of Rhode Island Red hens is very 
 similar to that of White Plymouth Rock hens, while the conformation 
 of White Leghorn hens is distinctly different. 
 
THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 
 coot- 
 
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86 
 
 BULLETIN No. 278 
 
 [June, 
 
 
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1938] 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 87 
 
 RELATIVE AND ABSOLUTE GROWTH OF THE DIFFERENT PARTS 
 OF THE CARCASS AND VISCERA 
 
 The growth of the different parts of the carcass and of the viscera 
 of the groups of cockerels, pullets, and capons is represented by the 
 average values given in Tables 12, 13, and 14. These tables include 
 the average weights for each group of 5 birds. Again the two lots of 
 1-pound birds have been averaged together, since the difference of two 
 weeks in their ages did not seem to affect the results materially.* Most 
 of the viscera and the different parts of the carcass increase continu- 
 ously with increasing body weight. For cockerels the rapid increase in 
 size of the testicles at about the 6-pound weight clearly indicates the 
 time of sexual maturity. The digestive organs are somewhat excep- 
 tional in their growth, since they reach their maximum size before the 
 bird has obtained its complete growth. This is true of all three groups 
 of birds. The weights of the gizzard and of the intestinal tract ex- 
 clusive of the gizzard reach their maximum when the weight of the 
 bird is 5 or 6 pounds. The weights of the spleen and liver increase 
 but little after this body weight is reached. This attainment of max- 
 imum growth of the digestive tract at a time when the body has not 
 ceased growing is also shown by the data in Table 15, relative to the 
 length of the intestinal tract. The maximum length of intestinal 
 tract seems to be reached at a weight of 5 pounds. 
 
 Data on the growth of the different parts of the carcass and the 
 different visceral organs, which show for each weight group the per- 
 centages of the empty weight of the bird reached by each organ and 
 each part of the carcass, are presented in Tables 16, 17, and 18. The 
 empty weight was obtained by deducting from the average live weight 
 
 *The average weights of the different organs and parts of carcass for the two 
 groups of birds of approximately the same weight (1 pound) but at different 
 ages, were as follows, all weights being given in grams: 
 
 Age 
 days 
 
 Body 
 weight 
 
 
 Blood 
 
 Feathers 
 
 Head 
 
 Shanks 
 + feet 
 
 Heart 
 
 Liver 
 
 Kidneys 
 
 Pan- 
 creas 
 
 Spleen 
 
 43... 
 57 
 
 446 
 
 452 
 
 21 
 19 
 
 18 
 16 
 
 19 
 20 
 
 23 
 23 
 
 3.0 
 2.9 
 
 16 
 15 
 
 4.5 
 
 1.9 
 1.7 
 
 0.8 
 1.1 
 
 ^ AgC 
 
 days 
 
 Viscera and offal (cont'd) 
 
 Dressed carcass 
 
 Lungs 
 
 Testi- 
 cles 
 
 Intestinal 
 tract 
 minus 
 gizzard 
 
 Gizzard 
 
 Contents 
 of intes- 
 inal tract 
 
 Neck 
 
 Skin 
 
 Legs 
 above 
 hock 
 
 Wings 
 
 Torso 
 
 43... 
 57 
 
 2.5 
 2.7 
 
 0.2 
 0.1 
 
 46 
 39 
 
 16 
 19 
 
 30 
 23 
 
 15 
 16 
 
 32 
 33 
 
 74 
 79 
 
 27 
 27 
 
 95 
 95 
 
 The total bone on the dressed carcass weighed 70 and 75 grams respectively 
 for the two groups of birds, while the total flesh on the dressed carcass weighed 
 131 and 138 grams respectively. 
 
88 
 
 BULLETIN No. 278 
 
 [June, 
 
 H 
 Z 
 
 
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 S 
 
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 03 .. 
 
 
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 Approximate slai 
 
 bO 
 
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 50 -t> 
 
 l| 
 
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 ' 
 
 Q | : :" : : : | : : : "o 
 < : E ! f : IsSJ : :Jl-g| 
 
 DRESSED CARCAS 
 Neck 
 Skin 
 Legs above ho 
 Wings 
 Torso 
 
 *^* p-j 
 
 Ijll 
 
 3 13-c 
 
 0-" 
 
THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 of each group of birds the average weight of the contents of the in- 
 testinal tract, including the gizzard. For convenience of study, the 
 organs and different parts of the carcass have been arranged into three 
 main groups: first, the offal, which in this tabulation, however, does 
 not include the inedible viscera; second, the visceral organs; and 
 third, the different parts of the dressed carcass. It is interesting to 
 note that the offal parts of the carcass constitute a fairly constant per- 
 centage of the empty live weight of the birds at all weights, namely, 
 very close to 19 percent. At the heavier weights there is a slight 
 
 TABLE 13. AVERAGE WEIGHTS OF PARTS OF CARCASS OF WHITE PLYMOUTH ROCK 
 PULLETS KILLED AT DIFFERENT WEIGHTS: EACH FIGURE Is AN AVERAGE 
 
 OF FIVE BIRDS 
 (All weights are in grams) 
 
 Approximate slaughter weight 
 
 2 
 
 3 
 
 4 
 
 5 
 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Age in days 
 
 73 
 
 94 
 
 189 
 
 219 
 
 Live weight in grams 
 
 961 
 
 1 342 
 
 1 842 
 
 2 340 
 
 VISCERA AND OFFAL 
 Blood 
 
 34 
 
 41 
 
 59 
 
 79 
 
 Feathers 
 
 66 
 
 108 
 
 152 
 
 168 
 
 Head 
 
 28 
 
 37 
 
 49 
 
 53 
 
 Shanks and feet ... . . . . 
 
 46 
 
 61 
 
 66 
 
 80 
 
 Heart 
 
 4.5 
 
 5.4 
 
 8.5 
 
 10.1 
 
 Liver 
 
 23 
 
 28 
 
 31 
 
 43 
 
 Kidneys 
 
 6.2 
 
 8.1 
 
 9.8 
 
 13.9 
 
 Pancreas 
 
 - 2.8 
 
 2 9 
 
 4.3 
 
 4.9 
 
 Spleen 
 
 2.4 
 
 3.0 
 
 3.3 
 
 4.8 
 
 Lungs 
 
 4 2 
 
 6 6 
 
 8 
 
 8.9 
 
 Intestinal tract exclusive of gizzard 
 
 65 
 
 83 
 
 108 
 
 128 
 
 Gizzard 
 
 39 
 
 47 
 
 60 
 
 65 
 
 Contents of digestive tract 
 
 46 
 
 49 
 
 55 
 
 95 
 
 DRESSED CARCASS 
 Neck 
 
 35 
 
 45 
 
 52 
 
 61 
 
 Skin 
 
 73 
 
 103 
 
 164 
 
 225 
 
 Legs above hock 
 
 167 
 
 258 
 
 344 
 
 428 
 
 Wings i 
 
 57 
 
 82 
 
 97 
 
 122 
 
 Torso 
 
 220 
 
 345 
 
 524 
 
 681 
 
 Total bone in carcass (except head, shanks, and 
 feet) 
 
 161 
 
 224 
 
 268 
 
 332 
 
 Total flesh and fat in carcass (except head, shanks, 
 and feet) 
 
 311 
 
 497 
 
 733 
 
 941 
 
 tendency for this percentage to decrease. This constancy in percent- 
 age weight is particularly apparent for the blood weights. Blood ap- 
 parently constitutes a consistently higher percentage of the empty 
 weight for the cockerels than for either capons or pullets, the capons 
 ranking next to the cockerels in this respect. 
 
 Following an initial increase from the .5-pound to 1-pound chicks, 
 the percentage weight of the total viscera shows a continuous decrease 
 
90 
 
 BULLETIN No. 27S 
 
 [June, 
 
 TABLE 14. AVERAGE WEIGHTS OF PARTS OF CARCASS OF WHITE PLYMOUTH ROCK 
 CAPONS KILLED AT DIFFERENT WEIGHTS: EACH FIGURE Is AN AVERAGE 
 
 OF FIVE BIRDS 
 (All weights are in grams) 
 
 Approximate slaughter weight 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Age in days 
 
 88 
 
 170 
 
 180 
 
 215 
 
 240 
 
 Live weight in grams 
 
 1 375 
 
 1 702 
 
 2 285 
 
 2 684 
 
 3 188 
 
 VISCERA AND OFFAL 
 Blood 
 
 54 
 
 67 
 
 96 
 
 91 
 
 113 
 
 Feathers 
 
 86 
 
 141 
 
 178 
 
 201 
 
 222 
 
 Head 
 
 40 
 
 51 
 
 57 
 
 60 
 
 70 
 
 Shanks and feet 
 
 77 
 
 88 
 
 111 
 
 129 
 
 124 
 
 Heart 
 
 6.1 
 
 6.9 
 
 9 1 
 
 11 
 
 13 6 
 
 Liver 
 
 32 
 
 36 
 
 49 
 
 51 
 
 70 
 
 Kidneys 
 
 8.4 
 
 10.2 
 
 12.1 
 
 14.1 
 
 16.2 
 
 Pancreas . . . 
 
 2 7 
 
 3 7 
 
 4 9 
 
 5 6 
 
 5 4 
 
 Spleen 
 
 2.8 
 
 4.1 
 
 4.6 
 
 5 9 
 
 6 4 
 
 Lungs 
 
 6 8 
 
 9 8 
 
 11 1 
 
 12 8 
 
 12 9 
 
 Intestinal tract exclusive of gizzard .... 
 Gizzard 
 
 84 
 47 
 
 93 
 
 57 
 
 133 
 61 
 
 158 
 74 
 
 152 
 79 
 
 Contents of intestinal tract 
 
 60 
 
 46 
 
 60 
 
 85 
 
 95 
 
 DRESSED CARCASS 
 Neck 
 
 48 
 
 58 
 
 69 
 
 82 
 
 89 
 
 Skin 
 
 99 
 
 136 
 
 191 
 
 228 
 
 272 
 
 Legs above hock 
 
 267 
 
 346 
 
 475 
 
 528 
 
 610 
 
 Wings 
 
 86 
 
 105 
 
 131 
 
 148 
 
 183 
 
 Torso 
 
 331 
 
 405 
 
 566 
 
 733 
 
 969 
 
 Total bone in carcass (except head, 
 shanks, and feet) 
 
 238 
 
 319 
 
 391 
 
 441 
 
 497 
 
 Total flesh and fat in carcass (except 
 head, shanks, and feet) 
 
 485 
 
 559 
 
 815 
 
 1 019 
 
 1 360 
 
 TABLE 15. LENGTH OF INTESTINAL TRACT OF WHITE PLYMOUTH ROCK CHICKENS 
 KILLED AT DIFFERENT WEIGHTS: EACH FIGURE Is AN AVERAGE OF 
 
 FIVE BIRDS 
 (All measurements are in centimeters) 
 
 Approximate slaughter 
 weight 
 
 0.5 
 
 Ib. 
 
 1 
 
 Ib. 
 
 1.5 
 
 Ibs. 
 
 2 
 Ibs. 
 
 3 
 Ibs. 
 
 4 
 Ibs. 
 
 5 
 Ibs. 
 
 6 
 Ibs. 
 
 7 
 Ibs. 
 
 
 
 
 
 
 
 
 
 
 
 COCKERELS 
 Intestines 
 
 102 
 
 134 
 
 142 
 
 149 
 
 166 
 
 176 
 
 189 
 
 184 
 
 174 
 
 Ceca (total) 
 
 21 
 
 26 
 
 32 
 
 34 
 
 35 
 
 42 
 
 49 
 
 45 
 
 45 
 
 PULLETS 
 Intestines 
 
 
 
 
 152 
 
 151 
 
 165 
 
 176 
 
 
 
 Ceca (total) 
 
 
 
 
 42 
 
 35 
 
 40 
 
 48 
 
 
 
 CAPONS 
 Intestines 
 
 
 
 
 
 162 
 
 165 
 
 190 
 
 193 
 
 198 
 
 Ceca (total) 
 
 
 
 
 
 40 
 
 38 
 
 61 
 
 50 
 
 48 
 
THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 91 
 
 
 
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92 
 
 BULLETIN No. 278 
 
 [June, 
 
 with increasing weight of the birds, this being true for all three groups 
 of birds. Jackson 1 and Donaldson 5 have shown that the relative 
 weight of the viscera decreases with increasing body weight in the case 
 of the albino rat, man, and other mammals. This relative decrease is 
 shown for all organs listed except the testicles, and is particularly pro- 
 nounced for the digestive tract. The decrease is not so marked for 
 the heart, kidneys, and lungs. 
 
 Donaldson 6 , has shown that the musculature contributes most to 
 the increasing weight of growing mammals. That the same is true for 
 growing fowls is indicated by the tables under discussion. The per- 
 centage weight of the total dressed carcass increases slightly but con- 
 
 TABLE 17. AVERAGE WEIGHTS OF PARTS OF CARCASS OF WHITE PLYMOUTH ROCK 
 
 PULLETS KILLED AT DIFFERENT WEIGHTS, EXPRESSED IN PERCENTAGE 
 
 OF THE EMPTY WEIGHT 
 
 Approximate slaughter weight 
 
 2 
 
 3 
 
 4 
 
 5 
 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Age in days 
 
 73 
 
 94 
 
 189 
 
 219 
 
 Percentage "fill" 
 
 4.8 
 
 3.7 
 
 2.6 
 
 3.7 
 
 Empty weight in grams 
 
 915 
 
 1 293 
 
 1 787 
 
 2 245 
 
 OFFAL 
 Feathers 
 
 percl. 
 7.2 
 
 percl. 
 8.4 
 
 percl. 
 8.5 
 
 perct. 
 7.5 
 
 Blood 
 
 3.7 
 
 3.2 
 
 3.3 
 
 3.5 
 
 Head 
 
 3.1 
 
 2.9 
 
 2.7 
 
 2.4 
 
 Shanks and feet 
 
 5.0 
 
 4.7 
 
 3.7 
 
 3.6 
 
 Tota> offal 
 
 19.0 
 
 19.1 
 
 18.2 
 
 16.9 
 
 VISCERA 
 Heart 
 
 0.49 
 
 0.42 
 
 0.48 
 
 0.45 
 
 Liver 
 
 2.5 
 
 2.2 
 
 1.7 
 
 1.9 
 
 Kidneys 
 
 0.68 
 
 0.63 
 
 0.55 
 
 0.62 
 
 Pancreas 
 
 0.31 
 
 0.22 
 
 0.24 
 
 0.22 
 
 Spleen 
 
 0.26 
 
 0.23 
 
 0.18 
 
 0.21 
 
 Lungs ; ' 
 
 0.46 
 
 0.51 
 
 0.45 
 
 0.40 
 
 Digestive tract 
 
 11.4 
 
 10.1 
 
 9.4 
 
 8.6 
 
 Total viscera 
 
 16.1 
 
 14.2 
 
 12.9 
 
 12.4 
 
 DRESSED CARCASS 
 Skin 
 
 8.0 
 
 8.0 
 
 9.2 
 
 10.0 
 
 Neck . 
 
 3.8 
 
 3.5 
 
 2.9 
 
 2.7 
 
 Legs above hock 
 
 18.3 
 
 20.0 
 
 19.3 
 
 19.0 
 
 Wings 
 
 6.2 
 
 6.3 
 
 5.4 
 
 5.4 
 
 Torso 
 
 24.0 
 
 26.7 
 
 29.3 
 
 30.2 
 
 Total dressed carcass 
 
 60.3 
 
 64.4 
 
 66.1 
 
 67.3 
 
 Total bone in dressed carcass 
 
 17.6 
 
 17.3 
 
 15.0 
 
 14.7 
 
 Total flesh and fat in dressed carcass 
 
 34.0 
 
 38.4 
 
 41.0 
 
 41.8 
 
 Total flesh, fat, and edible viscera 3 
 
 41.9 
 
 45.3 
 
 47.0 
 
 47.6 
 
 a lncluding heart, liver, gizzard, and kidneys. 
 
 tinuously with increasing weight of body. This increase is particularly 
 marked for the "torso. " a For the cockerels the relative weight of the 
 
 '"Torso" in this connection refers to the carcass of the bird minus the skin, 
 neck, legs, and wings. 
 
1926'} 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 93 
 
 legs above hock also increases steadily with increasing body weight, 
 while for the pullets and capons the percentage weight of the legs 
 above hock is practically constant for all body weights. The percent- 
 age weight of the skin also increases, while that for the wings decreases 
 for all three groups of birds. 
 
 That the relative increase in dressed carcass relates to the muscu- 
 lature and not to the bones is shown by the percentages at the bottom 
 
 TABLE 18. AVERAGE WEIGHTS OF PARTS OF CARCASS OF WHITE PLYMOUTH ROCK 
 
 CAPONS KILLED AT DIFFERENT WEIGHTS, EXPRESSED IN PERCENTAGE 
 
 OF THE EMPTY WEIGHT 
 
 Approximate slaughter weight 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Age in days 
 
 88 
 
 170 
 
 180 
 
 215 
 
 240 
 
 Percentage "fill" 
 
 4 4 
 
 2 7 
 
 2 6 
 
 3 5 
 
 3 
 
 Empty weight in grams 
 
 1 315 
 
 1 656 
 
 2 225 
 
 2 599 
 
 3 093 
 
 OFFAL 
 Feathers 
 
 perd. 
 6.5 
 
 perct. 
 8.5 
 
 perct. 
 8 
 
 perct. 
 
 7 8 
 
 perct. 
 7 2 
 
 Blood 
 
 4 1 
 
 4 
 
 4 3 
 
 3 5 
 
 3 7 
 
 Head 
 
 3.0 
 
 3.1 
 
 2.6 
 
 2.3 
 
 2.3 
 
 Shanks and feet 
 
 5.8 
 
 5.4 
 
 5.0 
 
 5.0 
 
 4 
 
 Total offal 
 
 19.5 
 
 21.0 
 
 19.9 
 
 18.6 
 
 17 1 
 
 VISCERA 
 Heart 
 
 46 
 
 42 
 
 41 
 
 42 
 
 44 
 
 Liver 
 
 2.4 
 
 2.2 
 
 2.2 
 
 1.9 
 
 2.3 
 
 Kidneys . . 
 
 64 
 
 62 
 
 54 
 
 54 
 
 52 
 
 Pancreas 
 
 0.21 
 
 0.22 
 
 0.22 
 
 0.22 
 
 17 
 
 Spleen 
 
 0.21 
 
 0.25 
 
 0.21 
 
 23 
 
 21 
 
 Lungs. . 
 
 52 
 
 59 
 
 0.50 
 
 49 
 
 42 
 
 Digestive tract 
 
 10 
 
 9 1 
 
 8 7 
 
 9 
 
 7 5 
 
 Total viscera 
 
 14 4 
 
 13 3 
 
 12 7 
 
 12 7 
 
 11 5 
 
 DRESSED CARCASS 
 Skin 
 
 7.5 
 
 8.2 
 
 8.6 
 
 8.8 
 
 8.8 
 
 Neck 
 
 3.6 
 
 3.5 
 
 3.1 
 
 3.2 
 
 2.9 
 
 Legs above hock 
 
 20 3 
 
 20.9 
 
 21.3 
 
 20.4 
 
 19 7 
 
 Wings 
 
 6 5 
 
 6 3 
 
 5.9 
 
 5.7 
 
 5 9 
 
 Torso 
 
 25 2 
 
 24 5 
 
 25.4 
 
 28 3 
 
 31 3 
 
 Total dressed carcass 
 
 63.2 
 
 64.6 
 
 64.4 
 
 66.4 
 
 68.6 
 
 Total bone in dressed carcass 
 
 18 1 
 
 19 3 
 
 17 6 
 
 17.0 
 
 16 1 
 
 Total flesh and fat in dressed carcass. . . . 
 Total flesh, fat, and edible viscera* 
 
 36.9 
 44,0 
 
 33.8 
 40.4 
 
 36.6 
 42.4 
 
 39.3 
 45.0 
 
 44.0 
 49.7 
 
 a lncluding heart, liver, gizzard, and kidneys. 
 
 of Tables 16, 17, and 18. For all three groups of birds the percentage 
 weight of the bone in the dressed carcass decreases with increasing 
 body weight, while the percentage weight of the total flesh and fat 
 increases. The relative weight of total flesh, fat, and edible viscera 
 (heart, liver, gizzard, and kidneys) also increases with increasing 
 weight of body. 
 
94 
 
 BULLETIN No. 278 
 
 [June, 
 
 -1 
 
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1926'} 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 95 
 
 The increase in weight of the different parts of the carcass and 
 the different visceral organs relative to the weights in the .5-pound 
 chicks is shown for the cockerels in Table 19. In this table the weights 
 for the different parts of the .5-pound chicks are taken as 100, and the 
 weights in the groups of increasing weight are expressed in percentage 
 of the corresponding weights in the .5-pound group. A study of Table 
 19 gives much the same information as the study just concluded. Thus, 
 
 TABLE 20. AVERAGE WEIGHTS OF PARTS OF CARCASS OF WHITE PLYMOUTH ROCK 
 PULLETS KILLED AT DIFFERENT WEIGHTS, EXPRESSED IN PERCENTAGE OF 
 THE CORRESPONDING WEIGHTS OF THE COCKERELS 
 
 Approximate slaughter weight 
 
 2 
 
 3 
 
 4 
 
 5 
 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Age in days 
 
 73 
 
 94 
 
 189 
 
 219 
 
 Empty weight in grams 
 
 94 
 
 99 
 
 104 
 
 105 
 
 OFFAL 
 Feathers 
 
 perci. 
 143 
 
 perct. 
 130 
 
 perct. 
 114 
 
 perct. 
 96 
 
 Blood 
 
 74 
 
 77 
 
 82 
 
 83 
 
 Head 
 
 85 
 
 86 
 
 91 
 
 87 
 
 Shanks and feet 
 
 82 
 
 74 
 
 69 
 
 71 
 
 Total off al 
 
 96 
 
 95 
 
 92 
 
 86 
 
 VISCERA 
 Heart 
 
 98 
 
 96 
 
 116 
 
 109 
 
 Liver 
 
 105 
 
 93 
 
 86 
 
 96 
 
 Kidneys 
 
 100 
 
 104 
 
 114 
 
 122 
 
 Pancreas 
 
 97 
 
 100 
 
 116 
 
 100 
 
 Spleen 
 
 126 
 
 111 
 
 114 
 
 120 
 
 Lungs 
 
 100 
 
 99 
 
 88 
 
 75 
 
 Gizzard 
 
 103 
 
 100 
 
 109 
 
 92 
 
 Digestive tract, total 
 
 99 
 
 100 
 
 113 
 
 101 
 
 Total viscera 
 
 94 
 
 99 
 
 106 
 
 100 
 
 DRESSED CARCASS 
 Skin 
 
 103 
 
 113 
 
 129 
 
 128 
 
 Neck 
 
 92 
 
 94 
 
 83 
 
 84 
 
 Legs above hock 
 
 86 
 
 92 
 
 90 
 
 90 
 
 Wings 
 
 92 
 
 94 
 
 86 
 
 96 
 
 Torso 
 
 103 
 
 113 
 
 123 
 
 127 
 
 Total dressed carcass 
 
 95 
 
 103 
 
 106 
 
 109 
 
 Total bone in dressed carcass 
 
 87 
 
 92 
 
 81 
 
 83 
 
 Total flesh and fat in dressed carcass 
 
 96 
 
 105 
 
 117 
 
 118 
 
 Total flesh, fat, and edible viscera 
 
 97 
 
 104 
 
 115 
 
 115 
 
 while the empty weight of the birds increases at a body weight of 7 
 pounds to a value 14.73 times the empty weight of .5-pound birds, the 
 total offal increases 13.67 times, the total viscera 6.77 times, and the 
 total dressed carcass 18.88 times. The bones in the carcass increase in 
 weight 13.08 times, while the total flesh and fat increase 27.09 times. 
 A comparison between the pullets, capons, and cockerels relative 
 to the weights of the different parts of the carcass and the different 
 
96 
 
 BULLETIN No. 278 
 
 [June, 
 
 visceral organs at different body weights, is afforded by the data given 
 in Tables 20 and 21. In these tables the weights of the different parts 
 and organs for each group of pullets and capons are expressed as per- 
 centages of the corresponding weights for the cockerels. 
 
 TABLE 21. AVERAGE WEIGHT OF PARTS OF CARCASS OF WHITE PLYMOUTH ROCK 
 
 CAPONS KILLED AT DIFFERENT WEIGHTS, EXPRESSED IN PERCENTAGE OF 
 
 THE CORRESPONDING WEIGHTS FOR THE COCKERELS 
 
 Approximate slaughter weight 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Age in days 
 
 88 
 
 170 
 
 180 
 
 215 
 
 240 
 
 Empty weight in grams 
 
 101 
 
 96 
 
 103 
 
 103 
 
 97 
 
 OFFAL 
 Feathers 
 
 perct. 
 104 
 
 perct. 
 105 
 
 perct. 
 102 
 
 perct. 
 99 
 
 perct. 
 121 
 
 Blood 
 
 102 
 
 93 
 
 101 
 
 86 
 
 75 
 
 Head 
 
 93 
 
 94 
 
 93 
 
 84 
 
 69 
 
 Shanks and feet 
 
 94 
 
 93 
 
 98 
 
 113 
 
 95 
 
 Total offal 
 
 98 
 
 98 
 
 100 
 
 97 
 
 93 
 
 VISCERA 
 Heart 
 
 109 
 
 94 
 
 98 
 
 98 
 
 65 
 
 Liver 
 
 107 
 
 100 
 
 109 
 
 100 
 
 167 
 
 Kidneys 
 
 108 
 
 119 
 
 106 
 
 108 
 
 131 
 
 Pancreas 
 
 93 
 
 100 
 
 100 
 
 127 
 
 100 
 
 Spleen .... 
 
 104 
 
 141 
 
 115 
 
 147 
 
 183 
 
 Lungs 
 
 101 
 
 108 
 
 93 
 
 113 
 
 94 
 
 Gizzard 
 
 100 
 
 104 
 
 86 
 
 109 
 
 120 
 
 Digestive tract 
 
 101 
 
 101 
 
 102 
 
 116 
 
 125 
 
 Total viscera 
 
 102 
 
 101 
 
 101 
 
 109 
 
 113 
 
 DRESSED CARCASS 
 Skin 
 
 109 
 
 107 
 
 109 
 
 120 
 
 100 
 
 Neck . . . 
 
 100 
 
 92 
 
 95 
 
 96 
 
 83 
 
 Legs above hock 
 
 95 
 
 91 
 
 100 
 
 95 
 
 77 
 
 Wings 
 
 99 
 
 93 
 
 103 
 
 99 
 
 100 
 
 Torso 
 
 109 
 
 95 
 
 105 
 
 111 
 
 113 
 
 Total dressed carcass 
 
 102 
 
 96 
 
 103 
 
 105 
 
 96 
 
 Total bone in dressed carcass 
 
 98 
 
 97 
 
 97 
 
 106 
 
 97 
 
 Total flesh and fat in dressed carcass. . . . 
 Total flesh, fat, and edible viscera 
 
 103 
 103 
 
 89 
 91 
 
 102 
 101 
 
 101 
 101 
 
 93 
 96 
 
 The weights of the total offal are consistently less for the pullets 
 than for the cockerels (Table 20) . This is true of each division of the 
 offal except the feathers. The weights of feathers for the pullets were 
 generally greater than those for the cockerels, the differences decreasing 
 with advancing body weight. The total weights of viscera did not 
 differ greatly for cockerels and pullets, this being particularly true of 
 the pancreas, liver, and the digestive tract. When the pullets reached 
 a weight of 2 pounds, their lungs weighed the same as the lungs of 
 the cockerels, but with increasing body weight the lungs of the cock- 
 erels weighed increasingly more than those of the pullets. Just the 
 
1926] 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 97 
 
 reverse is true with the kidneys, which were heavier in the pullets than 
 in the cockerels, the differences increasing with increasing body 
 weight. The weights of spleen were consistently heavier for the pul- 
 lets than for the cockerels. The dressed carcass in the pullets was al- 
 ways slightly heavier than in the cockerels for body weights of 3 
 pounds or more, this being entirely referable to the weights of the 
 skin and of torso. For the other parts of the carcass, particularly for 
 the neck, the cockerel weights are consistently greater than the pullet 
 weights. The weights of bone in the dressed carcass were always 
 
 TABLE 22. DIFFERENCES BETWEEN COCKERELS AND CAPONS WEIGHING SEVEN 
 
 POUNDS IN THE WEIGHTS OF CERTAIN VISCERAL ORGANS 
 
 (All weights are in grams) 
 
 Kind and 
 
 
 
 
 
 
 
 No. of 
 
 Heart 
 
 Liver 8 
 
 Spleen 
 
 Gizzard 
 
 Intestines 
 
 Kidneys 
 
 bird 
 
 
 
 
 
 
 
 COCKERELS 
 
 
 
 
 
 
 
 2115 
 
 26.0 
 
 45 
 
 3.4 
 
 66 
 
 69 
 
 13.0 
 
 2174 
 
 20.9 
 
 42 
 
 4.1 
 
 60 
 
 75 
 
 12.1 
 
 2713 
 
 21.4 
 
 48 
 
 4.0 
 
 70 
 
 91 
 
 14.8 
 
 2825 
 
 17.3 
 
 32 
 
 3.0 
 
 62 
 
 63 
 
 11.0 
 
 2111 
 
 19.9 
 
 41 
 
 3.1 
 
 72 
 
 59 
 
 11.3 
 
 CAPONS 
 
 
 
 
 
 
 
 2755 
 
 13.5 
 
 77 
 
 8 1 
 
 74 
 
 101 
 
 13 8 
 
 2152 
 
 15 7 
 
 66 
 
 7 
 
 78 
 
 136 
 
 16 8 
 
 2614 
 
 10 9 
 
 59 
 
 5 
 
 78 
 
 96 
 
 18 3 
 
 2482 
 
 12.7 
 
 73 
 
 7.1 
 
 67 
 
 94 
 
 13.6 
 
 2761 
 
 15.0 
 
 74 
 
 4.7 
 
 98 
 
 101 
 
 18.5 
 
 "The weight of gall bladder is included in the weight of liver. 
 
 greater at the same body weight for cockerels than for pullets, while 
 the total flesh and fat were always greater for the pullets at body 
 weights of 3 pounds or more. 
 
 The differences between cockerels and capons are not so consis- 
 tent as those between cockerels and pullets. The weights of offal were 
 much the same for capons and cockerels at all ages, except for the 
 weights of head and of blood, which at body weights of more than 5 
 pounds were greater in the cockerels than in the capons, the difference 
 increasing with increasing body weight. The weights of viscera also 
 were much the same for cockerels and capons for similar body weights, 
 except for the 7-pound weight, at which the total viscera for the capons 
 weighed 13 percent more than for the cockerels. 
 
 Some interesting differences between the two groups appear at the 
 7-pound weight with reference to the heart, liver, spleen, kidney, and 
 digestive tract. While the marked differences in the weights of heart, 
 kidney, and liver were only evident at the 7-pound weight, the differ- 
 ences in the weights of spleen and digestive tract were also evident at 
 smaller weights. For the spleen, in fact, the capons showed consist- 
 
98 
 
 BULLETIN No. 278 
 
 [June, 
 
 ently greater weights than the cockerels, from body weights of 3 to 
 7 pounds inclusive. To illustrate the great significance of these dif- 
 ferences in the two groups of birds at 7 pounds body weight, Table 22, 
 giving the individual weights for all ten birds, is presented. 
 
 Altho considerable variation is evident among the individual birds 
 in each group with respect to the weights of these visceral organs, the 
 differences between cockerels and capons are distinct. For example, 
 in the case of the heart all of the 5 cockerels showed larger weights 
 than any of the 5 capons, while in the case of the liver, spleen, and 
 
 TABLE 23. CHEMICAL COMPOSITION OF THE BONE SAMPLES 
 
 Kind of 
 bird 
 and weight 
 
 Dry 
 
 substance 
 
 Crude 
 protein 
 (Nx 6.0) 
 
 Ash 
 
 Ether 
 extract 
 
 Unac- 
 counted 
 for 
 
 Gross 
 energy 
 per gram 
 
 COCKERELS 
 Ibs. 
 0.5 
 
 perct. 
 39.97 
 
 perct. 
 19.68 
 
 perct. 
 8.81 
 
 perct . 
 4 57 
 
 perct. 
 6.91 
 
 small cals. 
 1 703 
 
 1 
 
 41.46 
 
 17 40 
 
 11.30 
 
 9 86 
 
 2.90 
 
 1 978 
 
 1 
 
 39.36 
 
 18.72 
 
 11 23 
 
 6 87 
 
 2.54 
 
 1 572 
 
 1.5 
 
 42.42 
 
 19.20 
 
 12.52 
 
 8.86 
 
 1.84 
 
 1 810 
 
 2 
 
 44.40 
 
 17.76 
 
 10.34 
 
 14 75 
 
 1.55 
 
 2 243 
 
 3 
 
 45.00 
 
 18.42 
 
 11.19 
 
 11 70 
 
 3.69 
 
 2 046 
 
 4 
 
 45.26 
 
 19.86 
 
 12.56 
 
 12 20 
 
 0.64 
 
 2 194 
 
 5 
 
 47.61 
 
 18.54 
 
 14.44 
 
 13.30 
 
 1.33 
 
 2 273 
 
 6 
 
 51.37 
 
 18.84 
 
 16.51 
 
 14 47 
 
 1.55 
 
 2 459 
 
 7 
 
 50.77 
 
 20.16 
 
 15.73 
 
 12 26 
 
 2.62 
 
 2 317 
 
 PULLETS 
 Ibs. , 
 2..Y. 
 
 45.40 
 
 18 18 
 
 11 35 
 
 13 57 
 
 2.30 
 
 2 145 
 
 3 
 
 44.35 
 
 18.00 
 
 10.07 
 
 13.57 
 
 2.71 
 
 2 185 
 
 4 
 
 51.86 
 
 17.76 
 
 12.70 
 
 18.30 
 
 3.10 
 
 2 505 
 
 5 
 
 54.87 
 
 18.78 
 
 14.30 
 
 20 00 
 
 1.79 
 
 2 955 
 
 CAPONS 
 Ibs. 
 3 
 
 44 40 
 
 18 30 
 
 10 84 
 
 13 40 
 
 1.86 
 
 2 223 
 
 4 
 
 46.75 
 
 18.24 
 
 11.82 
 
 13.54 
 
 3.15 
 
 2 491 
 
 5 
 
 48.12 
 
 18.72 
 
 11.57 
 
 16.15 
 
 1.68 
 
 2 628 
 
 6 
 
 50.76 
 
 18.84 
 
 14 65 
 
 15 33 
 
 1.94 
 
 2 597 
 
 7 
 
 52.95 
 
 17.34 
 
 11.86 
 
 21.62 
 
 2.07 
 
 2 919 
 
 intestines, all the capons showed larger weights than any of the cock- 
 erels. For the gizzard and kidney there is a slight overlapping by the 
 two groups, but nevertheless the differences appear to be highly sig- 
 nificant. Apparently castration has profoundly affected the growth 
 of these visceral organs, either directly or indirectly. 
 
 These differences in organ weights between capons and cockerels, 
 so far as they relate to the heart, spleen, and kidneys, are in agree- 
 ment with results reported by Marrassini and Luciani. 7 These authors 
 explain the hypertrophy of the spleen in castrated birds as a conse- 
 
THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 99 
 
 quence of the peritoneal hemorrhages often resulting from the removal 
 of the testicles in fowls. This explanation is hardly consistent, how- 
 ever, with the progressive divergence in spleen weights among cock- 
 erels and capons of increasing weight. The difference in heart weight 
 between castrated and uncastrated male birds may be reasonably ex- 
 plained as the result of a greater muscular activity of the cockerels. 
 Hatai 8 has shown that among groups of rats receiving different 
 
 TABLE 24. CHEMICAL COMPOSITION OF THE SAMPLES OF FLESH 
 AND EDIBLE VISCERA 
 
 Kind of 
 bird 
 and weight 
 
 Dry 
 
 substance 
 
 Crude 
 protein 
 (N x 6.0) 
 
 Crude 
 fat 
 
 Ash 
 
 Unac- 
 counted 
 for 
 
 Gross 
 energy 
 per gram 
 
 COCKERELS 
 Ibs. 
 0.5 
 
 perct. 
 30 07 
 
 perct. 
 20 88 
 
 perct. 
 4 38 
 
 perct. 
 1 44 
 
 perct. 
 3 37 
 
 small cals. 
 1 526 
 
 1 
 
 25.40 
 
 19.56 
 
 3.95 
 
 1.27 
 
 62 
 
 1 461 
 
 1 
 
 24.87 
 
 19.62 
 
 3.55 
 
 1.31 
 
 39 
 
 1 281 
 
 1.5 
 
 28.63 
 
 20.04 
 
 6 54 
 
 1 27 
 
 78 
 
 1 540 
 
 2 
 
 27 20 
 
 18 84 
 
 6 16 
 
 1 07 
 
 1 13 
 
 1 597 
 
 3 
 
 28.51 
 
 20.10 
 
 4.39 
 
 1.13 
 
 2.89 
 
 1 571 
 
 4 
 
 29.49 
 
 21.00 
 
 3.92 
 
 1.02 
 
 3 55 
 
 1 460 
 
 5 
 
 28.49 
 
 19.74 
 
 5 54 
 
 1 29 
 
 1 92 
 
 1 65 l a 
 
 6 
 
 28 51 
 
 20 22 
 
 5 40 
 
 1 72 
 
 1 17 
 
 1 714 
 
 7 
 
 28 08 
 
 21 00 
 
 4 46 
 
 1 40 
 
 1 22 
 
 1 606 
 
 PULLETS 
 Ibs. 
 2 
 
 26 70 
 
 19.02 
 
 6 00 
 
 1 06 
 
 62 
 
 1 515 
 
 3 
 
 34 09 
 
 18 90 
 
 9 75 
 
 1 20 
 
 4 24 
 
 1 860 
 
 4 
 
 30 79 
 
 18 54 
 
 11 22 
 
 1 01 
 
 02 
 
 2 262 
 
 5 
 
 33.67 
 
 20.22 
 
 12.62 
 
 1.35 
 
 -0 52 
 
 2 356 
 
 CAPONS 
 Ibs. 
 3 
 
 28 20 
 
 19 74 
 
 5 99 
 
 1 27 
 
 1 20 
 
 1 628 
 
 4 
 
 29 25 
 
 19 26 
 
 7 16 
 
 1 11 
 
 1 72 
 
 1 787 
 
 5 
 
 33 10 
 
 19 38 
 
 8 61 
 
 1 17 
 
 3 94 
 
 1 893 
 
 6. 
 
 31 43 
 
 18 84 
 
 10 29 
 
 98 
 
 1 32 
 
 2 049 
 
 7 
 
 36.97 
 
 18.00 
 
 16.84 
 
 0.94 
 
 1.19 
 
 2 543 
 
 "Calculated by using factors 5.7 calories per gram of protein and 9.5 calories per 
 gram of fat. 
 
 amounts of exercise, the weights of the heart observed were positively 
 correlated with the exercise records, while Hoskins 9 and Richter 10 have 
 shown, with the same species of animal, that castration markedly low- 
 ers spontaneous activity. 
 
 No clear differences exist between cockerels and capons with ref- 
 erence to the dressed carcass and its dissected parts, except possibly 
 with respect to the neck and the legs above hock, the weights of which 
 were, in general, less for the capons than for the cockerels, especially 
 at the 7-pound weight. Also, no consistent differences can be made 
 
100 
 
 BULLETIN No. 278 
 
 [June, 
 
 out between cockerels and capons in the weights of total bone or of 
 total flesh and fat in the dressed carcass. 
 
 CHEMICAL COMPOSITION OF THE BIRDS AT DIFFERENT WEIGHTS 
 
 Each group of 5 birds was analyzed in three composite samples: 
 
 first, the total bone of the dressed carcass; second, the flesh and fat of 
 
 the dressed carcass plus the heart, liver, and gizzard; and third, the 
 
 offal sample, including the blood, feathers, head, shanks and feet, gall 
 
 TABLE 25. CHEMICAL COMPOSITION OF THE SAMPLES OP OFFAL 
 
 Kind of 
 bird 
 and weight 
 
 Dry 
 
 substance 
 
 Crude 
 protein 
 (Nx 6.0) 
 
 Ash 
 
 Ether 
 extract 
 
 Unac- 
 counted 
 for 
 
 Gross 
 energy 
 per gram 
 
 COCKERELS 
 Ibs. 
 0.5 
 
 perct. 
 34.30 
 
 perct. 
 22.25 
 
 perct. 
 2.56 
 
 perct. 
 6.63 
 
 perct. 
 2 86 
 
 small cols. 
 1 762 
 
 1 
 
 29.74 
 
 21.12 
 
 2.36 
 
 7.67 
 
 -1.41 
 
 1 825 
 
 1 
 
 29.73 
 
 20.20 
 
 2.42 
 
 5.33 
 
 1.78 
 
 1 601 
 
 1.5 
 
 33.86 
 
 21.68 
 
 2.37 
 
 9.36 
 
 0.45 
 
 1 976 
 
 2 
 
 36.21 
 
 21.04 
 
 2.39 
 
 9.88 
 
 2 90 
 
 2 092 
 
 3.. 
 
 37.64 
 
 24.72 
 
 2.31 
 
 9.72 
 
 89 
 
 2 332 b 
 
 4 
 
 36.78 
 
 24.15 
 
 1.98 
 
 8.77 
 
 1.88 
 
 2 289 
 
 5 
 
 41.54 
 
 25.62 
 
 2.01 
 
 11.13 
 
 2.78 
 
 2 137 
 
 6 
 
 53.34 
 
 34.02 
 
 4.13 
 
 13.12 
 
 2 07 
 
 2 774 
 
 7 
 
 51.69 
 
 26.70 
 
 2.65 
 
 19.89 
 
 2 45 
 
 3 255 
 
 PULLETS 
 Ibs. 
 2 
 
 40.08 
 
 24.16 
 
 2.49 
 
 11.86 
 
 1.57 
 
 2 094 
 
 3 
 
 37.86 a 
 
 24 22 a 
 
 2.59 a 
 
 10.35 a 
 
 0.70 
 
 2 364 b 
 
 :H 
 
 49.94 
 51.86 
 
 25.83 
 27.71 
 
 1.89 
 1.82 
 
 19.14 
 23 07 
 
 3.08 
 74 
 
 2 758 
 3 516 
 
 CAPONS 
 Ibs. 
 3 
 
 38.08 
 
 23.72 
 
 2.60 
 
 10.98 
 
 0.78 
 
 2 280 
 
 4 
 
 40.65 
 
 24.12 
 
 2.02 
 
 12.12 
 
 2 39 
 
 2 736 
 
 5 
 
 42.18 
 
 22.29 
 
 1.85 
 
 14.86 
 
 3 18 
 
 2 803 
 
 6 
 
 54.18 
 
 29.45 
 
 2.34 
 
 18.99 
 
 3 40 
 
 3 120 
 
 7 
 
 51.37 
 
 25.85 
 
 2.22 
 
 20.87 
 
 2.43 
 
 3 396 
 
 a Chemical composition calculated from average composition of offal from 
 3-pound capons and cockerels. 
 
 b Calculated by using factors 5.7 calories per gram of protein and 9.5 calories per 
 gram of fat. 
 
 bladder, and the viscera not included in the second sample. These 
 samples were all ground in a fresh condition and submitted to routine 
 analysis. The percentage of dry substance in each sample was cor- 
 rected so far as possible for moisture losses during dissection, weigh- 
 ing, and grinding of the material. The gross energy of each sample 
 was also directly determined in the bomb calorimeter. The results of 
 these analyses and energy determinations are included in Tables 23, 
 24, and 25. Altho the percentage composition of these samples 
 
1926} 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 101 
 
 shows a good deal of irregularity in comparing birds of different weight, 
 there is a fairly general tendency for the dry substance to increase at 
 the heavier weights, and for the ether extract to increase in the samples 
 for the pullets and capons. No consistent increase in the ether ex- 
 tract of the cockerel samples was manifested after a weight of 2 
 
 TABLE 26. PERCENTAGE COMPOSITION OP LIVE BIRDS 
 
 Kind of bird 
 and weight 
 
 Age at 
 slaughter 
 
 Dry sub- 
 stance 
 
 Crude 
 protein 
 
 (Nx6.0) 
 
 Crude 
 fat 
 
 Ash 
 
 Unac- 
 counted 
 for 
 
 Gross 
 energy 
 per gram 
 
 CHICKS 
 gms. 
 37.5 
 
 days 
 1.5 
 
 perct. 
 24.89 
 
 perct. 
 16.18 
 
 perct. 
 5.60 
 
 perct. 
 1.83 
 
 perct. 
 1.28 
 
 small 
 cals. 
 
 1 476 
 
 COCKERELS 
 Ibs. 
 0.5 
 
 29 
 
 27.84 
 
 17.46 
 
 4.40 
 
 2 82 
 
 3.16 
 
 1 366 
 
 1 
 
 43 
 
 26.96 
 
 17 81 
 
 5 88 
 
 3 13 
 
 14 
 
 1 499 
 
 1 
 
 57 
 
 26 57 
 
 17 92 
 
 4 42 
 
 3 23 
 
 1 00 
 
 1 327 
 
 1.5 
 
 71 
 
 310.13 
 
 18.65 
 
 7.34 
 
 3.37 
 
 0.77 
 
 1 605 
 
 2 
 
 103 
 
 31.50 
 
 17.97 
 
 8.60 
 
 3.18 
 
 1.75 
 
 1 775 
 
 3 
 
 117 
 
 32.41 
 
 19.86 
 
 7.18 
 
 3 24 
 
 2.13 
 
 1 470 a 
 
 4 
 
 169 
 
 32.77 
 
 20 35 
 
 6 83 
 
 3 41 
 
 2 18 
 
 1 775 
 
 5 
 
 177 
 
 34 88 
 
 20 46 
 
 8 53 
 
 3 84 
 
 2 05 
 
 1 838 
 
 6 
 
 250 
 
 38 83 
 
 23 41 
 
 9 14 
 
 4 82 
 
 1 46 
 
 2 094 
 
 7 
 
 324 
 
 37.73 
 
 21.58 
 
 10.44 
 
 3.97 
 
 1.74 
 
 2 235 
 
 PULLETS 
 Ibs. 
 2 
 
 73 
 
 31 89 
 
 18 82 
 
 8 82 
 
 3 19 
 
 1 06 
 
 1 676 
 
 3 
 
 94 
 
 34 92 
 
 19 37 
 
 9 97 
 
 3 08 
 
 2 50 
 
 1 967 
 
 4 
 
 189 
 
 38 58 
 
 19 81 
 
 14 29 
 
 2 95 
 
 1 53 
 
 2 329 
 
 5 
 
 219 
 
 40.19 
 
 20.99 
 
 16.19 
 
 3.24 
 
 0.23 
 
 2 650 
 
 CAPONS 
 Ibs. 
 3 
 
 88 
 
 32 21 
 
 19 35 
 
 8 51 
 
 3 27 
 
 1 08 
 
 1 833 
 
 4 
 
 170 
 
 34 99 
 
 19 74 
 
 9 74 
 
 3 37 
 
 2 14 
 
 2 156 
 
 5 
 
 180 
 
 37 10 
 
 19 16 
 
 11 68 
 
 3 22 
 
 3 04 
 
 2 236 
 
 6 
 
 215 
 
 40 30 
 
 21 22 
 
 13 41 
 
 3 62 
 
 2 05 
 
 2 370 
 
 7 
 
 240 
 
 41.62 
 
 19.23 
 
 17.78 
 
 2.95 
 
 1.66 
 
 2 707 
 
 a The estimated energy value of this group, using average factors for protein 
 and fat, is 1,814 small calories per gram. 
 
 pounds was reached. The energy value per gram of the different 
 samples varied closely in accordance with their content of ether ex- 
 tract. 
 
 From the relative weights of the different samples for each group 
 of birds and their chemical composition, the composition of the live 
 birds was calculated. The values thus obtained are given in Table 
 26. For comparison, the average composition of 5 White Plymouth 
 Rock chicks shortly after hatching is given. These data on baby 
 
102 
 
 BULLETIN No. 278 
 
 [June, 
 
 chicks were obtained in connection with another experiment. The 
 percentage of dry substance increased very regularly with advancing 
 age and size, attaining higher figures for the pullets and capons than 
 for the cockerels. On the other hand, the percentages of ash and pro- 
 tein were generally larger for the cockerels than for the pullets or 
 capons for any given weight. Pullets show a much more marked ten- 
 
 TABLE 27 . PERCENTAGE COMPOSITION OF BIRDS ON BASIS OF EMPTY WEIGHT 
 
 
 
 Kind of bird 
 and weight 
 
 Dry 
 
 substance 
 
 Crude 
 protein 
 (Nx 6.0) 
 
 Crude 
 fat 
 
 Ash 
 
 Gross 
 energy 
 per gram 
 
 COCKERELS 
 Ibs. 
 5 
 
 perct. 
 29 94 
 
 perct. 
 18 77 
 
 perct. 
 4 75 
 
 perct. 
 3 00 
 
 small cak. 
 1 474 
 
 1 
 
 28.92 
 
 19.10 
 
 6.30 
 
 3.35 
 
 1 598 
 
 1 
 
 28.19 
 
 18.86 
 
 4.65 
 
 3.40 
 
 1 404 
 
 1.5 
 
 31.83 
 
 19.70 
 
 7.75 
 
 3.56 
 
 1 695 
 
 2 
 
 32.36 
 
 18.47 
 
 8.83 
 
 3.26 
 
 1 819 
 
 3 
 
 33 80 
 
 20 71 
 
 7 49 
 
 3 38 
 
 1 533 a 
 
 4 
 
 33 92 
 
 21 07 
 
 7 07 
 
 3 53 
 
 1 838 
 
 5.. 
 
 36.17 
 
 21.22 
 
 8.90 
 
 3.98 
 
 1 908 
 
 6 
 
 39.97 
 
 24.09 
 
 9.41 
 
 4.96 
 
 2 149 
 
 7 
 
 38.61 
 
 22.08 
 
 10.67 
 
 4.06 
 
 2 213 
 
 PULLETS 
 Ibs. 
 2 
 
 33 62 
 
 19 85 
 
 9 19 
 
 3 35 
 
 1 766 
 
 3 
 
 36 24 
 
 20 10 
 
 10 35 
 
 3 19 
 
 2 042 
 
 4 
 
 39 76 
 
 20 42 
 
 13 61 
 
 3 04 
 
 2 401 
 
 5.. 
 
 41 90 
 
 21 88 
 
 16 88 
 
 3 38 
 
 2 762 
 
 ,cJ 
 
 CAPONS 
 Ibs. 
 3 
 
 33.68 
 
 20 23 
 
 8 90 
 
 3 42 
 
 1 916 
 
 4 
 
 35 98 
 
 20 30 
 
 10 02 
 
 3 47 
 
 2 217 
 
 5 
 
 38 11 
 
 19 68 
 
 12 00 
 
 3 30 
 
 2 297 
 
 6 
 
 41 76 
 
 21 99 
 
 13 90 
 
 3 75 
 
 2 456 
 
 7 
 
 42.90 
 
 19.82 
 
 18.33 
 
 3.06 
 
 2 790 
 
 "The estimated energy value of this group, using average factors for protein 
 and fat, is 1,872 small calories per gram. 
 
 dency to fatten than cockerels, the capons occupying an intermediate 
 position in this respect (Table 26) . The energy value per gram of the 
 pullets for weights of 3 pounds or above were also distinctly higher 
 than the energy values for either cockerels or capons. 
 
 The close agreement between the composition of the two groups 
 of 1-pound cockerels killed two weeks apart is noteworthy, indicating 
 that the chemical as well as the anatomical composition of the birds 
 is more a function of the growth attained than of the age. In further 
 support of this statement, the distinct difference in chemical composi- 
 tion between the 1 -pound and 1.5-pound cockerels slaughtered two 
 weeks apart may be pointed out. 
 
1926} 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 103 
 
 For some purposes it is preferable to express the chemical com- 
 position of animals on the basis of the empty weights. This has been 
 done in Table 27 for the birds slaughtered in this experiment. The 
 differences between the values in Table 27 and those in Table 26, 
 however, are so small that they call for no further discussion. 
 
 TABLE 28. PERCENTAGE DISTRIBUTION OF DRY MATTER AND PROTEIN AMONG 
 
 (1) EDIBLE FLESH AND VISCERA, (2) BONES OF THE DRESSED CARCASS, 
 
 AND (3) OFFAL IN BIRD s OF DIFFERENT WEIGHTS AND SEX 
 
 
 
 Dry matter 
 
 
 
 Protein 
 
 
 Kind of bird 
 and weight 
 
 Edible 
 flesh, 
 etc. 
 
 Bones of 
 dressed 
 carcass 
 
 Offal 
 
 Edible 
 flesh, 
 etc. 
 
 Bones of 
 dressed 
 carcass 
 
 Offal 
 
 COCKERELS 
 Ibs. 
 0.5 
 
 perct. 
 33.6 
 
 perct. 
 23.7 
 
 perct. 
 42.7 
 
 perct. 
 37.2 
 
 perct. 
 18.6 
 
 perct. 
 44.2 
 
 1 
 
 35.0 
 
 24.1 
 
 40.9 
 
 41.1 
 
 16.3 
 
 42.6 
 
 1.5 
 
 36.5 
 
 22.8 
 
 40.7 
 
 41.2 
 
 16.7 
 
 42.1 
 
 2 
 
 33.2 
 
 26.1 
 
 40.7 
 
 40.2 
 
 18.3 
 
 41.4 
 
 3 
 
 35.6 
 
 24 8 
 
 39.6 
 
 41.0 
 
 16.5 
 
 42.5 
 
 4 
 
 36.1 
 
 25.5 
 
 38 3 
 
 41.5 
 
 18.0 
 
 40.5 
 
 5 
 
 33.6 
 
 24.6 
 
 41.8 
 
 39.7 
 
 16.3 
 
 44.0 
 
 6 
 
 32.3 
 
 21.4 
 
 46.3 
 
 38.0 
 
 13.0 
 
 49.0 
 
 7 
 
 34.7 
 
 21.1 
 
 44.2 
 
 45.3 
 
 14.6 
 
 40.0 
 
 PULLETS 
 Ibs. 
 2 
 
 32 9 
 
 23 9 
 
 43 2 
 
 39 7 
 
 16 2 
 
 44.1 
 
 3 
 
 41 6 
 
 21 1 
 
 37 2 
 
 41 6 
 
 15 5 
 
 42.9 
 
 4... . 
 
 35 9 
 
 19 5 
 
 44 5 
 
 42 1 
 
 13 
 
 44 8 
 
 5 
 
 37.7 
 
 19.3 
 
 42.9 
 
 43.4 
 
 12.7 
 
 43.9 
 
 CAPONS 
 Ibs. 
 3 
 
 36.0 
 
 23.8 
 
 40 2 
 
 42.0 
 
 16.3 
 
 41.7 
 
 4 
 
 33.1 
 
 25.0 
 
 41 9 
 
 38.6 
 
 17.3 
 
 44.1 
 
 5 
 
 36 2 
 
 23 4 
 
 40 4 
 
 41 1 
 
 17.6 
 
 41.3 
 
 6 
 
 33.4 
 
 20 6 
 
 45 9 
 
 38 
 
 14 6 
 
 47.4 
 
 7 
 
 41.3 
 
 19.6 
 
 39.1 
 
 43.5 
 
 13.9 
 
 42.6 
 
 The distribution of dry matter, protein, ether extract, energy, and 
 mineral matter among the three composite samples is expressed in per- 
 centages in Tables 28, 29, and 30. The offal sample contained a large 
 proportion, namely from 40 to 50 percent (average 41.7 percent), of 
 the dry substance in the birds at all weights. Furthermore, there is 
 no clear distinction between the different groups of birds in this re- 
 spect, nor can any progressive change in the percentage be noted with 
 increasing size and age. The edible part of the carcass contains an 
 average of 35.5 percent of the total dry matter, 40.8 percent of the 
 total protein, 30.2 percent of the total ether extract, and 37.2 percent 
 of the total gross energy of the birds at all weights. For the pullets, 
 
104 
 
 BULLETIN No. 278 
 
 [June, 
 
 the percentage of the total fat and energy contained in the edible 
 flesh and viscera seemed to be distinctly larger for weights of 3 pounds 
 and over, than the similar percentages for the cockerels and capons. 
 The mineral matter in the carcasses was contained largely in the bone 
 sample, which contained an average of 61.1 percent. The offal sample 
 ranked next with an average of 24.2 percent, and the edible flesh 
 
 TABLE 29. PERCENTAGE DISTRIBUTION OF ETHER EXTRACT AND GROSS ENERGY 
 AMONG (1) EDIBLE FLESH AND VISCERA, (2) BONES OF THE DRESSED 
 CARCASS, AND (3) OFFAL IN BIRDS OF DIFFERENT WEIGHTS 
 AND SEX 
 
 
 ] 
 
 3ther extrac 
 
 t 
 
 
 Gross energ 
 
 y 
 
 Amd. 01 
 bird and 
 weight 
 
 Edible 
 flesh, 
 etc. 
 
 Bones of 
 dressed 
 carcass 
 
 Offal 
 
 Edible 
 flesh, 
 etc. 
 
 Bones of 
 dressed 
 carcass 
 
 Offal 
 
 COCKERELS 
 Ibs. 
 0.5 
 
 perct. 
 30 9 
 
 perct. 
 17.1 
 
 perct. 
 52 
 
 perct. 
 34.6 
 
 perct. 
 20.8 
 
 perct. 
 44.7 
 
 1 
 
 27 3 
 
 26 1 
 
 46 7 
 
 35 
 
 20 2 
 
 44 8 
 
 1.5 
 
 34 2 
 
 19 5 
 
 46 3 
 
 36 9 
 
 18 3 
 
 44 8 
 
 2 
 
 27.5 
 
 31.8 
 
 40.7 
 
 34.7 
 
 23.4 
 
 41.9 
 
 3 
 
 24.8 
 
 29.0 
 
 46 2 
 
 43.2 
 
 24.8 
 
 32.0 
 
 4 
 
 23.1 
 
 33 1 
 
 43 9 
 
 33 1 
 
 22 8 
 
 44 1 
 
 5 
 
 26 6 
 
 27 9 
 
 45 6 
 
 37 
 
 22 2 
 
 40 8 
 
 6 
 
 26.0 
 
 25.6 
 
 48.4 
 
 36.1 
 
 19.1 
 
 44.8 
 
 7 
 
 19.9 
 
 18.4 
 
 61.6 
 
 34.6 
 
 16.8 
 
 48.6 
 
 PULLETS 
 Ibs. j 
 2... L 
 
 27 1 
 
 26 2 
 
 46 7 
 
 35 5 
 
 21 5 
 
 43 
 
 3 
 
 41 7 
 
 22 7 
 
 35 6 
 
 40 3 
 
 18 5 
 
 41 2 
 
 4 
 
 35.3 
 
 18.6 
 
 46.1 
 
 43.7 
 
 15.6 
 
 40.7 
 
 5 
 
 35.1 
 
 17.5 
 
 47.4 
 
 40 
 
 15.8 
 
 44.2 
 
 CAPONS 
 Ibs. 
 3. ... 
 
 29 
 
 27 2 
 
 43 8 
 
 36 6 
 
 21 
 
 42 4 
 
 4 
 
 29.2 
 
 26.1 
 
 44.9 
 
 32.7 
 
 21.6 
 
 45.7 
 
 5 
 
 29.9 
 
 24.9 
 
 45.1 
 
 34.4 
 
 21 2 
 
 44.4 
 
 6.. . 
 
 32.8 
 
 18 7 
 
 48 4 
 
 37 
 
 18 
 
 45 
 
 7 
 
 44.0 
 
 18.8 
 
 37.2 
 
 43.7 
 
 16.6 
 
 39.7 
 
 sample contained only 14.7 percent. In general, the percentage of the 
 mineral matter of the carcass contained in the bones of the dressed 
 carcass tended to increase with increasing size and age, while the per- 
 centage contained in the offal tended to decrease. 
 
 From the chemical composition of the flesh and fat of the dressed 
 carcass and of the edible viscera (exclusive of heart and kidneys) , and 
 from the weights of this fraction of the carcass (corrected to even body 
 weights) , the total edible nutrients in White Plymouth Rock chickens 
 of different live weights may be calculated. The results of such a cal- 
 culation are given in Table 31. The outstanding feature of this tab- 
 
THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 105 
 
 ulation is the demonstration of the superiority of pullets in their con- 
 tent of edible fat and energy, unaccompanied by any inferiority in the 
 content of edible protein. Capons rank next to pullets in regard to 
 the content of edible fat and energy, but are inferior to cockerels in 
 the content of edible protein. 
 
 Altho the different groups of birds were killed at average weights 
 approximating closely the weights given in the left column of the 
 tables just considered, it was only an approximation. In computing 
 
 TABLE 30. PERCENTAGE DISTRIBUTION OF MINERAL MATTER AMONG (1) EDIBLE 
 FLESH AND VISCERA, (2) BONES OF THE DRESSED CARCASS, AND (3) OFFAL 
 IN BIRDS OF DIFFERENT WEIGHTS AND SEX 
 
 
 
 Crude ash 
 
 
 Kind of bird 
 and weight 
 
 Edible 
 flesh, 
 etc. 
 
 Bones of 
 dressed 
 carcass 
 
 Offal 
 
 COCKERELS 
 Ibs. 
 0.5 
 
 perct. 
 16.1 
 
 perct. 
 52.2 
 
 perct. 
 31.7 
 
 1 
 
 15.2 
 
 57.1 
 
 27.7 
 
 1.5 
 
 14.4 
 
 60.1 
 
 25.5 
 
 2 
 
 13.0 
 
 60.4 
 
 26.7 
 
 3 
 
 14.1 
 
 61.6 
 
 24.3 
 
 4 
 
 12.0 
 
 68.1 
 
 19.8 
 
 5 
 
 13.9 
 
 67.8 
 
 18.4 
 
 6 
 
 15.7 
 
 55.4 
 
 28.9 
 
 7 
 
 16.4 
 
 62.0 
 
 21.6 
 
 PULLETS 
 Ibs. 
 2 
 
 13.0 
 
 60.1 
 
 26.9 
 
 3 
 
 16 6 
 
 54.5 
 
 28.9 
 
 4 
 
 15.4 
 
 62.6 
 
 22.1 
 
 5 
 
 18.8 
 
 62.5 
 
 18.7 
 
 CAPONS 
 Ibs. 
 3 
 
 16.0 
 
 57.1 
 
 26.9 
 
 4 
 
 13.0 
 
 65.5 
 
 21.5 
 
 5 
 
 14 8 
 
 64.8 
 
 20.4 
 
 6 
 
 11 6 
 
 66.3 
 
 22.1 
 
 7 
 
 14.7 
 
 61.6 
 
 23.7 
 
 the composition of gains within any weight interval of the cockerels, 
 pullets, and capons, it is necessary to compute the composition of 
 birds at the exact weights under consideration. This is done in Table 
 32 by applying the percentages contained in Table 26 to the even 
 weights of .5, 1, 1.5, and 2 pounds, etc. The total energy content per 
 bird has been estimated (at each weight) from the content of the crude 
 protein and crude fat (Table 32, last column) . In this estimation the 
 energy values of protein and fat have been taken as 5.7 and 9.5 cal- 
 
106 
 
 BULLETIN No. 278 
 
 [June, 
 
 ories per gram, respectively. These factors have been used by Armsby 
 for similar computations on the larger farm animals. A comparison 
 of this column of figures with the gross energy content as directly de- 
 termined gives some idea concerning the size of error that would be 
 made in applying these average factors to the protein and fat of 
 chicken carcasses. As a general rule, the estimated energy content is 
 higher than the content as directly determined, the average difference 
 amounting to 3.6 percent. 
 
 TABLE 31.- 
 
 -EDIBLE NUTRIENTS IN WHITE PLYMOUTH ROCK BIRDS OF DIFFERENT 
 WEIGHTS AND SEX 
 
 Kind of 
 bird and 
 weight 
 
 Weight of 
 flesh and 
 edible 
 viscera 
 
 Dry 
 
 matter 
 
 Crude 
 protein 
 
 Crude 
 fat 
 
 Ash 
 
 Gross 
 energy 
 
 COCKERELS 
 Ibs. 
 0.5 
 
 gms. 
 64 
 
 gms. 
 19 4 
 
 gms. 
 13 4 
 
 gms. 
 2 8 
 
 gms. 
 9 
 
 cals. 
 98 
 
 1 
 
 166 
 
 42.1 
 
 32.4 
 
 6.5 
 
 2.1 
 
 242 
 
 1> . . . 
 
 177 
 
 43 9 
 
 34 6 
 
 6 3 
 
 2 3 
 
 226 
 
 1.5 
 
 254 
 
 72.6 
 
 50.8 
 
 16 6 
 
 3 2 
 
 391 
 
 2 
 
 348 
 
 94 8 
 
 65 6 
 
 21 5 
 
 3 7 
 
 556 
 
 3 
 
 551 
 
 157 
 
 111 
 
 24.2 
 
 6.2 
 
 866 
 
 4 
 
 729 
 
 215 
 
 153 
 
 28 6 
 
 7 4 
 
 1 064 
 
 5 
 
 934 
 
 266 
 
 184 
 
 51.7 
 
 12.0 
 
 1 542 
 
 6 
 
 1 198 
 
 342 
 
 242 
 
 64 7 
 
 20.6 
 
 2 053 
 
 7 
 
 1 480 
 
 416 
 
 311 
 
 66 
 
 20 7 
 
 2 376 
 
 PULLETS 
 Ibs. } 
 2 
 
 356 
 
 95.2 
 
 67.8 
 
 21.4 
 
 3.8 
 
 540 
 
 3 
 
 580 
 
 198 
 
 110 
 
 56 6 
 
 6.1 
 
 1 079 
 
 4 
 
 811 
 
 250 
 
 150 
 
 91 
 
 8 2 
 
 1 834 
 
 5 
 
 1 022 
 
 344 
 
 207 
 
 129 
 
 13 8 
 
 2 408 
 
 CAPONS 
 Ibs. 
 3 
 
 561 
 
 158 
 
 111 
 
 33.6 
 
 7.1 
 
 913 
 
 4 
 
 718 
 
 210 
 
 138 
 
 51 4 
 
 8.0 
 
 1 283 
 
 5 
 
 922 
 
 305 
 
 179 
 
 79 4 
 
 10 8 
 
 1 745 
 
 6 
 
 1 166 
 
 366 
 
 220 
 
 120 
 
 11 4 
 
 2 389 
 
 7 
 
 1 477 
 
 546 
 
 266 
 
 249 
 
 13.9 
 
 3 755 
 
 The data in Table 32 must form the basis for the estimation of 
 the composition of successive gains in weight of the birds from .5 to 
 7 pounds. They are too irregular, however, to permit of accurate esti- 
 mates, mainly because of the small size of the groups of birds ana- 
 lyzed at each weight. Under these circumstances it is to be expected 
 that the error in computing the composition of successive small gains 
 in weight from such data would be considerable. For example, the 
 error in assuming that the 5 cockerels killed and analyzed at a weight 
 of 5 pounds possessed the same composition at a weight of 4 pounds 
 
THE GROWTH OP WHITE PLYMOUTH ROCK CHICKENS 
 
 107 
 
 as the 5 other cockerels killed at that weight, will be contained in full 
 in the estimate of the composition of the gain from 4 to 5 pounds. 
 This error, inherent in slaughter experiments of this type, may be de- 
 creased only by increasing the number of birds killed at each weight 
 or by smoothing off the data obtained on the smaller groups of birds 
 by the proper mathematical procedure. The latter expedient was 
 adopted, and it was found that the relation between the content of 
 the birds in dry matter, protein, etc., and the live weight of the bird, 
 
 TABLE 32. CALCULATED COMPOSITION OP THE BIRDS AT EVEN WEIGHTS 
 
 Kind of 
 bird and 
 weight 
 
 Dry 
 
 sub- 
 stance 
 
 Crude 
 protein 
 (Nx 6.0) 
 
 Crude 
 fat 
 
 Ash 
 
 Unac- 
 counted 
 for 
 
 Gross 
 energy 
 
 Esti- 
 mated 
 gross 
 energy" 
 
 COCKERELS 
 Ibs. 
 0.5 
 
 gms. 
 63 
 
 gms. 
 40 
 
 gms. 
 10 
 
 gms. 
 6 
 
 gms. 
 
 7 
 
 therms 
 31 
 
 therms 
 32 
 
 1 
 
 121 
 
 81 
 
 23 
 
 14 
 
 3 
 
 64 
 
 68 
 
 1.5 
 
 205 
 
 127 
 
 50 
 
 23 
 
 5 
 
 1 09 
 
 1 20 
 
 2 
 
 286 
 
 163 
 
 78 
 
 29 
 
 16 
 
 1 61 
 
 1 67 
 
 3 
 
 441 
 
 270 
 
 98 
 
 44 
 
 29 
 
 2 00 
 
 2 47 
 
 4 
 
 594 
 
 369 
 
 124 
 
 62 
 
 39 
 
 3 22 
 
 3 28 
 
 5 
 
 791 
 
 464 
 
 195 
 
 86 
 
 46 
 
 4 32 
 
 4 50 
 
 6 
 
 1 057 
 
 637 
 
 249 
 
 131 
 
 40 
 
 5 70 
 
 6 00 
 
 7 
 
 1 198 
 
 685 
 
 331 
 
 126 
 
 56 
 
 7 10 
 
 7 05 
 
 PULLETS 
 Ibs. 
 2 
 
 289 
 
 171 
 
 80 
 
 29 
 
 9 
 
 1 52 
 
 1 73 
 
 3 
 
 475 
 
 264 
 
 136 
 
 42 
 
 33 
 
 2 68 
 
 2 80 
 
 4 
 
 700 
 
 359 
 
 259 
 
 54 
 
 28 
 
 4 22 
 
 4 51 
 
 5 
 
 912 
 
 476 
 
 367 
 
 74 
 
 5 
 
 6 01 
 
 6 20 
 
 CAPONS 
 Ibs. 
 3 
 
 438 
 
 263 
 
 116 
 
 45 
 
 14 
 
 2 49 
 
 2 60 
 
 4 
 
 635 
 
 358 
 
 177 
 
 61 
 
 39 
 
 3 91 
 
 3 72 
 
 5 
 
 842 
 
 435 
 
 265 
 
 73 
 
 69 
 
 5 07 
 
 5 00 
 
 6 
 
 1 097 
 
 578 
 
 365 
 
 99 
 
 55 
 
 6 45 
 
 6 76 
 
 7 
 
 1 322 
 
 611 
 
 565 
 
 94 
 
 52 
 
 8.59 
 
 8.85 
 
 "These values were estimated by using factors 5.7 calories per gram for protein 
 and 9.5 calories per gram for fat. 
 
 can be very well represented for the range of live weight included in 
 this experiment by a parabolic equation of the type y = ax -\- bx 2 . 
 
 This equation has been fitted to each of the relations between the 
 different chemical constituents and live weight for each of the three 
 groups of birds. In dealing with the results for pullets and capons, 
 it has been assumed that pullets weighing less than 2 pounds would 
 have the same composition as cockerels of equal weight, and that the 
 composition of capons before castration is well represented by the 
 composition of the cockerels slaughtered between .5 and 2 pounds in- 
 clusive. The equation has been fitted to each set of experimental data 
 
108 
 
 BULLETIN No. 278 
 
 [June, 
 
 by the method of least squares. A graphical picture of the closeness 
 of fit of the mathematical curves to the experimental data is given in 
 Figs. 1 to 5 inclusive.* 
 
 An inspection of these charts seems to indicate that the closeness 
 of fit of the curves to the experimental data is satisfactory. The fact 
 that the relation between the content of these birds in any given nutri- 
 ent, and the slaughter weight, is such that it can well be represented 
 by a mathematical equation of this simple type, again testifies to the 
 
 TABLE 33. COMPOSITION OF THE BIRDS AT EVEN WEIGHTS AS COMPUTED FROM 
 MATHEMATICAL EQUATIONS FITTED TO THE DATA IN TABLE 31 
 
 Kind of 
 bird and 
 weight 
 
 Dry 
 
 substance 
 
 Crude 
 protein 
 
 Crude 
 fat 
 
 Ash 
 
 Unac- 
 counted 
 for 
 
 Gross 
 energy 
 
 COCKERELS 
 Ibs. 
 5... 
 
 gms. 
 64 2 
 
 gms. 
 41.2 
 
 gms. 
 12.4 
 
 gms. 
 6.7 
 
 gms. 
 3.9 
 
 cals. 
 290 
 
 1 
 
 131.7 
 
 83.5 
 
 26.4 
 
 13.7 
 
 8.1 
 
 615 
 
 1.5 
 
 202.4 
 
 127.1 
 
 42.0 
 
 21.1 
 
 12.2 
 
 971 
 
 2.. 
 
 276.5 
 
 171.9 
 
 59.2 
 
 28.9 
 
 16.5 
 
 1 361 
 
 3 
 
 434.4 
 
 265.1 
 
 98.5 
 
 45.5 
 
 25.3 
 
 2 239 
 
 4 
 
 605.4 
 
 363.1 
 
 144.4 
 
 63.6 
 
 34.3 
 
 3 249 
 
 5 
 
 789.4 
 
 465.9 
 
 196.6 
 
 83.1 
 
 43.8 
 
 4 390 
 
 6 
 
 986.6 
 
 573.6 
 
 255.4 
 
 104.0 
 
 53 6 
 
 5 663 
 
 7 
 
 1 196.9 
 
 686.1 
 
 320.7 
 
 126.4 
 
 63.7 
 
 7 067 
 
 8 
 
 1 420.3 
 
 803.4 
 
 392.4 
 
 150.5 
 
 74.0 
 
 8 603 
 
 PULLETS 
 Ibs. 
 0.5..?. 
 
 62.6 
 
 39.8 
 
 9.6 
 
 6.8 
 
 6.4 
 
 276 
 
 1 
 
 131.8 
 
 81.2 
 
 25.4 
 
 13.8 
 
 11.4 
 
 624 
 
 1.5 
 
 207.5 
 
 124.3 
 
 47.2 
 
 20.8 
 
 15 2 
 
 1 043 
 
 2 
 
 289.8 
 
 169.1 
 
 75.1 
 
 27.9 
 
 17.7 
 
 1 534 
 
 3 
 
 474.1 
 
 263.7 
 
 149.2 
 
 42.4 
 
 18.8 
 
 2 732 
 
 4 
 
 684.6 
 
 365.0 
 
 247.7 
 
 57.1 
 
 14.8 
 
 4 218 
 
 5 
 
 921.4 
 
 472.9 
 
 370.5 
 
 72.2 
 
 5.8 
 
 5 990 
 
 6 
 
 1 184.5 
 
 587.5 
 
 517.7 
 
 87.6 
 
 -8.3 
 
 8 050 
 
 CAPONS 
 Ibs. 
 0.5 
 
 61.1 
 
 43.0 
 
 6.4 
 
 8.0 
 
 3 7 
 
 313 
 
 1 
 
 127.5 
 
 86.0 
 
 17.7 
 
 15.8 
 
 8.0 
 
 671 
 
 1.5 
 
 199.1 
 
 129.3 
 
 33 8 
 
 23 4 
 
 12 6 
 
 1 073 
 
 2 
 
 275.9 
 
 172.6 
 
 54.7 
 
 30.9 
 
 17.7 
 
 1 520 
 
 3 
 
 445.4 
 
 259.8 
 
 111.0 
 
 45.2 
 
 29.4 
 
 2 546 
 
 4 
 
 635.9 
 
 347.4 
 
 186.7 
 
 58.8 
 
 43.0 
 
 3 750 
 
 5 
 
 847.3 
 
 435.6 
 
 281.7 
 
 71.6 
 
 58.4 
 
 5 132 
 
 6... 
 
 1 079.8 
 
 524.4 
 
 396.1 
 
 83 7 
 
 75 6 
 
 6 692 
 
 7 
 
 1 333.3 
 
 613.7 
 
 529.8 
 
 95 1 
 
 94 7 
 
 8 430 
 
 8 
 
 1 607.8 
 
 703.5 
 
 682.9 
 
 105.7 
 
 115.7 
 
 10 346 
 
 *Jn determining the constants of the equations, no account was taken of 
 the experimental data for the 6-pound cockerels relating to dry matter, crude 
 protein, and ash, or of the data for the 6-pound capons relating to protein and 
 ash. These results appear to be so far out of line with the others as to justify 
 their exclusion. 
 
1926] 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 109 
 
no 
 
 BULLETIN No. 278 
 
 [June, 
 
 9 uj 
 
 - O 
 
1926] 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 111 
 
 conclusion that the composition of birds is more closely related to the 
 growth attained than to the age. 
 
 By means of the mathematical equations fitting the various sets 
 of experimental results contained in Table 32, it is possible to estimate 
 the composition of birds at even weights, obtaining in this way a 
 smoothed set of data from which the composition of successive gains 
 may be computed with greater accuracy than from the unsmoothed 
 experimental data themselves. This has been done in Table 33. The 
 
 Body Weight of Cockerels in Pounds 
 _z A 3 6 7 6 
 
 945676 
 
 Body Weight of Capons in Pounds 
 
 FIG. 5 
 
 composition of the three groups of birds at weights 1 pound heavier 
 than the greatest actual slaughter weight has been estimated by the 
 mathematical equations. Any more extensive extrapolation, however, 
 would not be advisable. Corrected estimates of the percentage com- 
 position of the birds at successive even weights may be computed 
 from the data in Table 33. This has been done in Table 34. Table 35 
 contains the estimates of the composition of the successive pound gains 
 in weight of cockerels, pullets, and capons based upon the smoothed 
 data contained in Table 33. The content of the successive pound gains 
 
112 
 
 BULLETIN No. 27S 
 
 [June, 
 
 in dry matter, protein, fat, ash, and energy increases in a linear fashion 
 with the live weight of the birds, a result which follows from the fact 
 that the relation between the content of the birds in each of these 
 constituents and the live weight may be represented by a parabolic 
 equation.* 
 
 It is evident that the energy value of the gains put on by pullets 
 exceeds the energy value of gains for the other two groups of birds, 
 while the capon gains rank next in this respect. For example, the gain 
 from 4 to 5 pounds on the pullets contained a decidedly greater gross 
 energy content than the 7- to 8-pound gain on the cockerels, and was 
 
 TABLE 34. PERCENTAGE COMPOSITION OF THE BIRDS AT EVEN WEIGHTS COMPUTED 
 
 FROM TABLE 33 
 
 Kind of bird 
 and weight 
 
 Dry 
 
 substance 
 
 Crude 
 protein 
 
 Crude 
 fat 
 
 Ash 
 
 Unac- 
 counted 
 for 
 
 Gross 
 energy 
 per gram 
 
 COCKERELS 
 Ibs. 
 0.5 
 
 perct. 
 28.31 
 
 perct. 
 18.17 
 
 perct. 
 5.47 
 
 perct. 
 2.95 
 
 perct. 
 1.72 
 
 small cals. 
 1 279 
 
 1 
 
 29.03 
 
 18.41 
 
 5.82 
 
 3.02 
 
 1.78 
 
 1 356 
 
 1.5 
 
 29 75 
 
 18 68 
 
 6 17 
 
 3.10 
 
 1 80 
 
 1 427 
 
 2 
 
 30.48 
 
 18.95 
 
 6.53 
 
 3.19 
 
 1.81 
 
 1 500 
 
 3 
 
 31.92 
 
 19.48 
 
 7.24 
 
 3.34 
 
 1.86 
 
 1 645 
 
 4 
 
 33.37 
 
 20.01 
 
 7.96 
 
 3.51 
 
 1.89 
 
 1 791 
 
 5 
 
 34.81 
 
 20.54 
 
 8.67 
 
 3.66 
 
 1.94 
 
 1 936 
 
 6 
 
 36.25 
 
 21.08 
 
 9.38 
 
 3.82 
 
 1.97 
 
 2 081 
 
 7 
 
 37.70 
 
 21.61 
 
 10 10 
 
 3.98 
 
 2.01 
 
 2 226 
 
 8...J 
 
 39.14 
 
 22.14 
 
 10.81 
 
 4.15 
 
 2.04 
 
 2 371 
 
 PULLETS 
 Ibs. 
 0.5 
 
 27.60 
 
 17 55 
 
 4 23 
 
 3 00 
 
 2.82 
 
 1 217 
 
 1 
 
 29.06 
 
 17.90 
 
 5.60 
 
 3.04 
 
 2.52 
 
 1 376 
 
 1.5 ,. 
 
 30.50 
 
 18.27 
 
 6.94 
 
 3.06 
 
 2.23 
 
 1 533 
 
 2 
 
 31.94 
 
 18.64 
 
 8 28 
 
 3.08 
 
 1.94 
 
 1 691 
 
 3 
 
 34.84 
 
 19 38 
 
 10 96 
 
 3 12 
 
 1.38 
 
 2 008 
 
 4 
 
 37.73 
 
 20.12 
 
 13 65 
 
 3 15 
 
 81 
 
 2 325 
 
 5 
 
 40.63 
 
 20.85 
 
 16.34 
 
 3.18 
 
 0.26 
 
 2 641 
 
 6 
 
 43.52 
 
 21.59 
 
 19.02 
 
 3.22 
 
 -0.31 
 
 2 958 
 
 CAPONS 
 Ibs 
 0.5 
 
 26.94 
 
 18.96 
 
 2 82 
 
 3 53 
 
 1 63 
 
 1 380 
 
 1 
 
 28.11 
 
 18.96 
 
 3.90 
 
 3.48 
 
 1.77 
 
 1 479 
 
 1.5 
 
 29 26 
 
 19 00 
 
 4 97 
 
 3 44 
 
 1 85 
 
 1 577 
 
 2 
 
 30.41 
 
 19.03 
 
 6 03 
 
 3 41 
 
 1.94 
 
 1 675 
 
 3 
 
 32.73 
 
 19.09 
 
 8 16 
 
 3 32 
 
 2 16 
 
 1 871 
 
 4 
 
 35.05 
 
 19.15 
 
 10 30 
 
 3 24 
 
 2 36 
 
 2 067 
 
 5 
 
 37 36 
 
 19 21 
 
 12 42 
 
 3 16 
 
 2 57 
 
 2 263 
 
 6 
 
 39 68 
 
 19 27 
 
 14 55 
 
 3 08 
 
 2 78 
 
 2 459 
 
 7 
 
 41 99 
 
 19 33 
 
 16 69 
 
 3 00 
 
 2 97 
 
 2 655 
 
 8 
 
 44.31 
 
 19.39 
 
 18.82 
 
 2.91 
 
 3.19 
 
 2 851 
 
 *See Lipka, J., "Graphical and Mechanical Computation," p. 146. 
 Wiley and Sons, 1918. 
 
 John 
 
1926} 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 113 
 
 slightly greater than the 6- to 7-pound gain on the capons. This re- 
 lation of the energy content of gains is directly related to their content 
 in crude fat. Evidently pullets fatten at a much more rapid rate 
 than either cockerels or capons. As an illustration of this fact, 
 the 5- to 6-pound gain on the pullets contained over twice as 
 much fat as the 7- to 8-pound gain on the cockerels. At the same 
 time, the pullet gains contained larger amounts of protein than the 
 
 TABLE 35. COMPOSITION OF SUCCESSIVE POUND GAINS IN WEIGHT COMPUTED 
 
 FROM TABLE 33 
 
 Kind of 
 bird 
 
 Gain 
 from 
 
 Dry sub- 
 stance 
 
 Crude 
 protein 
 
 Crude 
 fat 
 
 Ash 
 
 Unac- 
 counted 
 for 
 
 Gross 
 energy 
 
 COCKERELS 
 
 Ibs. 
 to 1 
 
 gms. 
 131.7 
 
 gms. 
 83.5 
 
 gms. 
 26 4 
 
 gms. 
 13 7 
 
 gms. 
 8 1 
 
 cals. 
 615 
 
 PULLETS 
 
 1 to 2 
 2 to 3 
 3 to 4 
 4 to 5 
 5 to 6 
 6 to 7 
 7 to 8 
 
 to 1 
 
 144.8 
 158.1 
 171.0 
 184.0 
 197.2 
 210.3 
 223 A 
 
 131 8 
 
 88.4 
 93.2 
 98.0 
 102.8 
 107.7 
 112.5 
 117.3 
 
 81 2 
 
 32.8 
 39.3 
 45.9 
 52.2 
 58.8 
 65.3 
 71.7 
 
 25 4 
 
 15.2 
 16.6 
 18.1 
 19.5 
 20.9 
 22.4 
 24.1 
 
 13 8 
 
 8.4 
 9.0 
 9.0 
 9.5 
 9.8 
 10.1 
 10.3 
 
 11 4 
 
 746 
 878 
 1 010 
 1 141 
 1 273 
 1 404 
 1 536 
 
 624 
 
 CAPONS 
 
 1 to 2 
 2 to 3 
 3 to 4 
 4 to 5 
 5 to 6 
 
 to 1 
 
 158.0 
 184.3 
 210.5 
 236.8 
 263.1 
 
 127 5 
 
 87.9 
 94.6 
 101.3 
 107.9 
 114.6 
 
 86 
 
 49.7 
 74.1 
 98.5 
 122.8 
 147.2 
 
 17 7 
 
 14.1 
 14.5 
 14.7 
 15.1 
 15.4 
 
 15 8 
 
 6.3 
 1.1 
 -4.0 
 -9.0 
 -14.1 
 
 8 
 
 910 
 1 198 
 1 486 
 1 772 
 2 060 
 
 671 
 
 
 1 to 2 
 2 to 3 
 3 to 4 
 4 to 5 
 5 to 6 
 6 to 7 
 7 to 8 
 
 148.4 
 169.5 
 190.5 
 211.4 
 232.5 
 253.5 
 274.5 
 
 86.6 
 
 87.2 
 87.6 
 88.2 
 88.8 
 89.3 
 89.8 
 
 37.0 
 56.3 
 75.7 
 95.0 
 114.4 
 133.7 
 153.1 
 
 15.1 
 14.3 
 13.6 
 12.8 
 12.1 
 11.4 
 10.6 
 
 9.7 
 11.7 
 13.6 
 15.4 
 17.2 
 19.1 
 21.0 
 
 849 
 1 026 
 1 204 
 1 382 
 1 560 
 1 738 
 1 916 
 
 cockerel gains, the capon gains ranking last in this respect. This is 
 probably related to the fact that the growth of the pullets represented 
 more of an increase in muscular tissue and less of an increase in bone 
 than the growth of the cockerels. 
 
 It is interesting to note that the protein content of the capon gains 
 was very nearly constant thruout the range of growth covered in 
 this experiment. On the other hand, the cockerels outranked all other 
 birds in the ash content of their gains, which increased markedly, 
 while the ash content of the pullet gains was very nearly constant. 
 The computed ash content of the capon gains decreased from begin- 
 ning to end, but the authors do not attach any great significance 
 to this apparent decrease, because it was evidently dependent upon 
 whether or not the erratic result on the 6-pound capons was consid- 
 
114 
 
 BULLETIN No. 278 
 
 [June, 
 
 ered in determining the constants in the parabolic equation relating 
 to the crude ash content of the birds. The dry matter content of the 
 pullet gains exceeded slightly the dry matter content of the capon 
 gains at equal weight intervals, and greatly exceeded the dry matter 
 content of the cockerel gains. 
 
 The results compiled in Table 35 are expressed on a percentage 
 basis in Table 36. These figures reveal the same relationships that 
 
 TABLE 36. PERCENTAGE COMPOSITION OF SUCCESSIVE POUND GAINS IN WEIGHT 
 COMPUTED FROM TABLE 35 
 
 Kind of bird 
 
 Gain 
 from 
 
 Dry sub- 
 stance 
 
 Crude 
 protein 
 
 Crude 
 fat 
 
 Ash 
 
 Unac- 
 counted 
 for 
 
 Gross 
 energy 
 per gram 
 
 COCKERELS 
 
 Zfe. 
 
 to 1 
 
 perct. 
 29 03 
 
 perct. 
 18.41 
 
 perct. 
 5 82 
 
 perct. 
 3 02 
 
 perct. 
 1 78 
 
 small 
 cals. 
 1 356 
 
 PULLETS 
 
 1 to 2 
 2 to 3 
 3 to 4 
 4 to 5 
 5 to 6 
 6 to 7 
 7 to 8 
 
 to 1 
 
 31.92 
 34.85 
 37.70 
 40.57 
 43.47 
 46.36 
 49.25 
 
 29 06 
 
 19.49 
 20.55 
 21.60 
 22.66 
 23.74 
 24.80 
 25.86 
 
 17 90 
 
 7.23 
 8.66 
 10.11 
 11.50 
 12.96 
 14.40 
 15.81 
 
 5 60 
 
 3.35 
 3.66 
 3.99 
 4.30 
 4.61 
 4.94 
 5.31 
 
 3 04 
 
 1.85 
 1.98 
 2.00 
 2.11 
 2.16 
 2.22 
 2.27 
 
 2 52 
 
 1 645 
 1 936 
 2 227 
 2 515 
 2 806 
 3 095 
 3 386 
 
 1 376 
 
 ^ 
 CAPONS 
 
 1 to 2 
 2 to 3 
 3 to 4 
 4 to 5 
 5 to 6 
 
 to 1 
 
 34.83 
 40.63 
 46.41 
 52.20 
 58.00 
 
 28 11 
 
 19.38 
 20.86 
 22.33 
 23.79 
 25.26 
 
 18 96 
 
 10.96 
 16.34 
 21.72 
 27.07 
 32.45 
 
 3 90 
 
 3.11 
 3.20 
 3.24 
 3.33 
 3.40 
 
 3 48 
 
 1.38 
 0.23 
 -0.88 
 -1.99 
 -3.11 
 
 1 77 
 
 2 006 
 2 641 
 3 276 
 3 907 
 4 541 
 
 1 479 
 
 
 1 to 2 
 2 to 3 
 3 to 4 
 4 to 5 
 5 to 6 
 6 to 7 
 7 to 8 
 
 32.72 
 37.37 
 42.00 
 46.61 
 51.26 
 55.89 
 60.52 
 
 19.09 
 19.22 
 19.31 
 19.44 
 19.58 
 19.69 
 19.80 
 
 8.16 
 12.41 
 16.69 
 20.94 
 25.22 
 29.48 
 33.75 
 
 3.33 
 3.15 
 3.00 
 2.82 
 2.67 
 2.51 
 2.34 
 
 2.14 
 2.59 
 3.00 
 3.41 
 3.79 
 4.21 
 4.63 
 
 1 872 
 2 262 
 2 654 
 3 047 
 3 439 
 3 832 
 4 224 
 
 have already been pointed out. The change in percentage composi- 
 tion of gains with increasing body weight is illustrated graphically in 
 Figs. 6 and 7. 
 
 RATE OF RETENTION OF NUTRIENTS DURING GROWTH 
 
 The practical value of estimates of the composition of gains in 
 weight of growing animals depends upon the possibility of determin- 
 ing from such data the requirements of growing animals for nutri- 
 ment. It seems obvious that the amount of energy added to the body 
 of a growing animal daily at different ages is a fair estimate of the 
 amount of net food energy required, above that used for maintenance, 
 
1926] 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 115 
 
 s 
 
 O 
 
 s 
 
 
 
 Qfl 
 
 -CD 
 
116 BULLETIN No. 278 [June, 
 
 to sustain normal growth. Such values have been used in this way 
 by Armsby in computing his feeding standards for growth and fat- 
 tening. Obviously they are of practical significance only when the 
 net energy value of ordinary farm feeds in covering growth require- 
 ments is known. Nevertheless, the determination of the daily reten- 
 tion of energy by growing animals is a necessary step in any accurate 
 system of expressing the nutritive requirements of such animals. 
 
 It seems a logical extension of Armsby's system to take the daily 
 retention of protein and mineral matter as a scientific measure of the 
 needs of growing animals for these nutrients, even tho Armsby him- 
 self did not extend his energy conceptions in this manner. It is per- 
 haps no idle hope that some day it will be possible to express the net 
 protein value of feeds for growth in a manner quite analogous to the 
 expression of their net energy values. Less optimism must be felt that 
 the mineral values of feeds can ever be so simply expressed. 
 
 The calculation of the daily retention of nutrients by White Ply- 
 mouth Rock birds evidently .depends upon two determinations: first, 
 the determination of the composition of successive gains in weight; 
 and second, the determination of the rate of gain in weight at differ- 
 ent ages. The results of the former determination have already been 
 considered. The latter determination must evidently depend upon 
 the data given in Table 1. However, there is the same objection to 
 using the original observations contained in this table as there was 
 to the use of the experimental results contained in Table 32. This 
 objection rests in the fact that experimental observations upon 
 animals are subject to a considerable variation produced by casual 
 factors, related either to the animal or to its environment, that can- 
 not be brought under experimental control. These casual variations 
 render uncertain to some degree the significance of any single experi- 
 mental observation. In removing this type of variation as it relates 
 to the data on the composition of the birds at increasing live weights, 
 given in Table 32, the method used was to fit a mathematical curve 
 to the experimental data. The same method will be used in smooth- 
 ing out the growth observations on the entire flock of White Plymouth 
 Rock birds. 
 
 The mathematical procedure, however, is not so simple in this 
 case, because the growth data are not so readily represented by a 
 simple mathematical equation as were the chemical data. It has been 
 previously pointed out that the rate of growth of the birds exhibited 
 a more or less periodical fluctuation. The first point to settle, there- 
 fore, in smoothing off the data, is whether these periodical fluctuations 
 are entirely casual in so far as they relate simply to uncontrolled en- 
 vironmental factors, or whether they are related to the growth of 
 White Plymouth Rock birds regardless of environmental changes. The 
 authors have already expressed a hesitancy in attaching any great sig- 
 
1926] THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 117 
 
 nificance to these fluctuations, because they cannot be interpreted 
 either one way or the other with any degree of assurance, since it is an 
 undoubted fact that weather conditions show a periodical variation. 
 
 The belief that uncontrolled environmental factors may entirely 
 account for the apparent cyclic property of the growth curve of White 
 Plymouth Rock birds is strengthened by a comparison of the Illinois 
 data with those obtained at the Purdue Agricultural Experiment Sta- 
 tion, to which reference has already been made. In Figs. 8 and 9 such 
 a comparison is made graphically. In these charts the successive bi- 
 weekly gains in weight expressed in grams are represented by rect- 
 angles of proportionate size. In the case of the Illinois data two suc- 
 cessive biweekly gains have occasionally been combined in an at- 
 tempt to smooth out some particularly irregular variation in the rate 
 of growth. The Purdue data have been interpreted by Kempster and 
 Henderson 11 as indicating the existence of two cycles of growth. This 
 interpretation is illustrated by the curve roughly drawn thru the tops 
 of the rectangles in the different sections of Fig. 9. These curves have 
 been patterned as closely as possible after the curves drawn by the 
 above mentioned authors in illustrating their conclusion. On the other 
 hand, the Illinois data obviously cannot be considered as supporting 
 any theory that the growth of White Plymouth Rock birds exhibits 
 only two cycles. The growth obtained may, in fact, be better repre- 
 sented by an assumption of three cycles, as illustrated by the irregular 
 curves drawn thru the tops of the rectangles in Fig. 8. 
 
 The marked discrepancy between these two sets of growth data 
 obtained on birds of the same breed may be taken to indicate that 
 the cycles of growth observed are more probably related to periodical 
 variations in environmental factors than to periodical variations in 
 the growth impulse itself. It was decided, therefore, to smooth off the 
 growth data without regard to these periodical fluctuations in the rate 
 of growth. The growth curve of both the Illinois and Purdue flocks 
 is generally of an elongated S type, but unfortunately it cannot be 
 represented thruout its entire range by the S type curve used by 
 
 / 
 
 Robertson 12 , i.e., log = K (t tj in which x is the growth ac- 
 
 A x 
 
 complished at any time, t, A is a constant equal to the maximum value 
 of x, and ^ is a constant equal to t when x equals one-half A. When 
 this equation is fitted to the entire growth data of either investigation, 
 a very poor fit results for ages of 12 weeks or less. The expedient finally 
 used in overcoming this error, therefore, was to fit the above equation 
 first, to the first 10 or 12 weeks of growth, and second, to the growth 
 subsequent to this period. The equations obtained by this procedure 
 and a graphical presentation of the closeness of fit secured are con- 
 tained in Figs. 10 and 11. The junction of the two curves for each 
 
118 
 
 BULLETIN No. 278 
 
 [June. 
 
 *s* 
 
 *-5d 
 
 ^3 
 
 OQ. 
 
 o 
 
 O 
 
 P 
 
 
 5? 
 
 
 . 
 
 /f 
 
 7 
 
 
 \ 
 
 
 
 \ 1 
 
 ) 
 
 / 
 
 I/ 
 
 
 
 1 
 
 |\ 
 
 
 
 1 
 
 M 
 
 
 1 
 e /A vj i 
 
 a IX 
 
 X, 
 
 K^ 
 
 p. <u 
 
 0> 
 
 ^ 
 
 a) 
 "OO 
 
 9UJX2JO 
 
19S8} 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 119 
 
120 BULLETIN No. 278 [June, 
 
 set of data has no mathematical significance. The use of Robertson's 
 growth curve in this way obviously is purely empirical. 
 
 The equations obtained in this manner have been used in estimat- 
 ing the ages at which even pound weights are attained by White Ply- 
 mouth Rock birds according to the Illinois and the Purdue data. The 
 results thus secured are given in Table 37. The average time re- 
 quired to make successive pound gains in weight have been computed 
 from the data in Table 37 and compiled in Table 38. 
 
 From the data shown in Table 35, i. e., the composition of suc- 
 cessive pound gains in weight, and in Table 38, the average time re- 
 quired to make successive pound gains in weight,. the daily retention 
 of protein, ash, and energy has been computed.* Table 39 contains 
 these results. In applying the results of the computed composition 
 of successive gains in weight to the Purdue growth data, the assump- 
 tion is made that the composition of a bird at a given weight is not 
 appreciably dependent on the time required to reach that weight; in 
 other words, that it is largely independent of the age of the bird. This 
 assumption is, of course, only approximately true. However, the re- 
 sults obtained in this experiment bear out this assumption, particu- 
 larly the close agreement in composition between the two groups of 
 1-pound birds killed two weeks apart. It must be admitted, however, 
 that the results in Table 39 based upon the Illinois growth data are 
 open to the criticism that the growth secured was apparently subnor- 
 mal, while the results based on the Purdue data are open to the criti- 
 cism that the assumption just considered has not been firmly estab- 
 lished, especially for birds of the same weight but differing widely in age. 
 
 The abnormally large daily retention of protein, ash, and energy 
 for cockerels weighing 2.5 pounds, indicated by a computation based 
 upon the Purdue growth data, may be explained from the fact that in 
 the Purdue experiment the cockerels and pullets were not separated 
 until the tenth week of age. The Illinois growth data indicate that 
 
 'Obviously, in computing the average daily retention of nutrients up to 1 
 pound in weight, the composition of the gain from to 1 pound, as given in 
 Table 35, must be corrected for the composition of the bird at hatching. As- 
 suming the hatching weight of White Plymouth Rock birds to be 38 grams, 
 based upon the Purdue data, their composition in grams may be computed by 
 means of the parabolic equations deduced from our own chemical data, with 
 the following results: 
 
 Dry Crude Crude Gross 
 
 matter protein fat Ash energy 
 
 Calculated 10.56 6.83 1.97 1.10 47 
 
 Observed 9.46 6.15 2.13 0.70 56 
 
 The observed values given in this tabulation are computed from the average 
 composition of 5 White Rock chicks averaging 1V days in age (Table 32). The 
 calculated daily retention of nutrients of .5-pound chicks is therefore based upon 
 the estimated composition of 1-pound chicks minus this estimate of the com- 
 position of chicks shortly after hatching. 
 
1926] 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 121 
 
 TABLE 37. AVERAGE AGES AT WHICH EVEN POUND WEIGHTS ARE REACHED BY 
 WHITE PLYMOUTH ROCK BIRDS 
 
 
 ] 
 
 llinois dati 
 
 l 
 
 ] 
 
 'urdue dat 
 
 a 
 
 
 Cockerels 
 
 Pullets 
 
 Capons 
 
 Cockerels 
 
 Pullets 
 
 Capons 
 
 Ibs. 
 1 
 
 days 
 54 
 
 days 
 60 
 
 days 
 
 days 
 49 a 
 
 days 
 49 a 
 
 days 
 
 2 
 
 101 
 
 112 
 
 102 
 
 73 a 
 
 73 a 
 
 
 3 
 
 140 
 
 158 
 
 140 
 
 88 
 
 105 
 
 92 
 
 4 
 
 177 
 
 223 
 
 177 
 
 111 
 
 135 
 
 114 
 
 5.... 
 
 221 
 
 
 221 
 
 135 
 
 175 
 
 135 
 
 6... 
 
 305 
 
 
 304 
 
 164 
 
 260 
 
 158 
 
 7 
 
 
 
 
 
 
 187 
 
 8 
 
 
 
 
 
 
 242 
 
 a The cockerels and pullets were not separated in the Purdue experiment until 
 the tenth week. 
 
 cockerels grow faster than puilets even in the earlier weeks of life, so 
 that the abnormally rapid gain apparently put on by the Purdue cock- 
 erels in the period immediately succeeding their separation from the 
 pullets is probably a great exaggeration of the actual gain. 
 
 The daily retention of protein by growing cockerels averages a 
 little over 2 grams according to the Illinois growth data, and about 
 twice as much according to the Purdue growth data. The daily re- 
 tention of mineral matter varies from .2 to .5 gram in one series, and 
 from .3 to about 1 gram in the other. The daily retention of energy 
 increases in both sets of data from 10 to 12 calories to 27 calories in 
 the Illinois estimates, and to 44 calories according to the Purdue esti- 
 mates (neglecting the abnormal figure for the 2.5-pound birds) ; after 
 which a decrease in the rate of retention occurs according to the Illi- 
 nois growth data. The Purdue growth data indicate a sustained max- 
 imum retention. 
 
 For the pullets and capons a slightly smaller daily retention of 
 protein and mineral matter is indicated than for the cockerels. Altho 
 
 TABLE 38. AVERAGE TIME REQUIRED BY WHITE PLYMOUTH ROCK BIRDS TO MAKE 
 SUCCESSIVE POUND GAINS IN WEIGHT 
 
 Gains 
 
 Illinois data 
 
 Purdue data 
 
 Cockerels 
 
 Pullets 
 
 Capons 
 
 Cockerels 
 
 Pullets 
 
 Capons 
 
 Ibs. 
 Hatching to 1 
 Ito2 
 
 days 
 54 
 47 
 39 
 37 
 44 
 84 
 
 days 
 60 
 52 
 46 
 65 
 
 days 
 
 '38 
 37 
 44 
 83 
 
 days 
 49 
 24 
 15 
 23 
 24 
 29 
 
 days 
 49 
 24 
 32 
 30 
 40 
 85 
 
 days 
 
 'i9 
 22 
 21 
 23 
 29 
 55 
 
 2 to 3 
 
 3 to 4 
 
 4 to 5 
 
 5 to 6 
 
 6 to 7 
 
 7 to 8 
 
 
122 
 
 BULLETIN No. 278 
 
 [June, 
 
 the gains on the pullets, especially at the higher weights, contained 
 more energy than the gains on the cockerels, this is almost exactly 
 offset by the slower rate at which the pullets grew, so that little con- 
 sistent difference is evident in the daily retention of energy by cock- 
 erels and pullets. The greater energy content of the gains of capons 
 as compared with cockerels is not offset by a slower growth, so that the 
 values in Table 39 indicate a larger daily retention of energy by ca- 
 pons than by cockerels of like weight. 
 
 TABLE 39. DAILY RETENTION OF PROTEIN, ASH, AND ENERGY BY WHITE PLYMOUTH 
 ROCK BIRDS OF DIFFERENT WEIGHTS 
 
 Kind of bird 
 and weight 
 
 Illinois data 
 
 Purdue data 
 
 Age 
 
 Protein 
 
 Ash 
 
 Energy 
 
 Age 
 
 Protein 
 
 Ash 
 
 Energy 
 
 COCKERELS 
 Ibs. 
 0.5 
 
 days 
 34 
 89 
 122 
 158 
 197 
 250 
 
 34 
 85 
 132 
 183 
 
 gms. 
 1.42 
 1.88 
 2.39 
 2.65 
 2.34 
 1.28 
 
 1.24 
 1.69 
 2.06 
 1.56 
 
 gms. 
 0.23 
 0.32 
 0.43 
 0.49 
 0.44 
 0.25 
 
 0.21 
 0.27 
 0.32 
 0.23 
 
 cals. 
 10.5 
 15.9 
 22.5 
 27.3 
 25.9 
 15.2 
 
 9.6 
 17.5 
 26.0 
 22.9 
 
 days 
 32 
 61 
 75 
 99 
 122 
 148 
 
 32 
 62 
 89 
 120 
 153 
 204 
 
 80 
 103 
 124 
 146 
 172 
 209 
 
 gms. 
 1.57 
 3.68 
 6.21 
 4.26 
 4.28 
 3.71 
 
 1.52 
 3.66 
 2.96 
 3.38 
 2.70 
 1.35 
 
 4.59 
 3.98 
 4.20 
 3.86 
 3.08 
 1.63 
 
 qms. 
 0.26 
 0.63 
 1.11 
 0.79 
 0.81 
 0.72 
 
 0.26 
 0.59 
 0.45 
 0.49 
 0.38 
 0.18 
 
 0.75 
 0.62 
 0.61 
 0.53 
 0.39 
 0.19 
 
 cals. 
 11.6 
 31.1 
 58.5 
 43.9 
 47.5 
 43.9 
 
 11.8 
 37.9 
 37.4 
 49.5 
 44.3 
 24.2 
 
 54.0 
 54.7 
 65.8 
 67.8 
 59.9 
 34.8 
 
 1.5 
 
 2.5 
 
 3.5 
 
 4.5 
 
 5.5 
 
 PULLETS 
 Ibs. 
 0.5 
 
 1.5 
 
 2.5 
 
 3j5 
 
 4.5 
 
 5.5 
 
 
 
 
 
 CAPONS 
 Ibs. 
 2.5 
 
 120 
 157 
 195 
 249 
 
 2.29 
 2.37 
 2.00 
 1.07 
 
 0.38 
 0.37 
 0.29 
 0.15 
 
 27.0 
 32.5 
 31.4 
 
 18.8 
 
 3.5 .. 
 
 4.5 
 
 5.5 
 
 6.5 
 
 7.5 
 
 
 
 
 
 It is of interest to compare the rate of retention of protein by 
 growing White Plymouth Rock chickens with the rate of retention of 
 protein by other species of farm animals. Armsby 13 has made an ex- 
 tensive compilation of such data for cattle, sheep, and swine, and has 
 found that when the daily retention is expressed in terms of gain of 
 protein per 1,000 pounds live weight per day, the change in rate of 
 
 135 
 
 retention is fairly well represented by the equation, a = ; in 
 
 a-f-20 
 
 which g is the gain of protein in pounds per day per 1,000 pounds live 
 weight, and a is the age in days. This equation corresponds fairly 
 
1926} 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
 123 
 
 well with the general average of the observed results on cattle and 
 sheep, especially for the later ages. With swine the few results 
 available appear to indicate a greater rate of protein retention during 
 the first three months than would be predicted from this equation. 
 
 A comparison of the daily retention of protein per pound of live 
 weight calculated from this equation, with the daily retention of pro- 
 
 TABLE 40. CALCULATED AND OBSERVED DAILY RETENTION OF PROTEIN PER POUND 
 LIVE WEIGHT BY WHITE PLYMOUTH ROCK COCKERELS 
 
 Body weight 
 
 Illinois data 
 
 Purdue data 
 
 Protein retention per day 
 per pound body weight 
 
 Protein retention per day 
 per pound body weight 
 
 Age 
 
 Observed 
 
 Calculated 8 
 
 Age 
 
 Observed 
 
 Calculated 3 
 
 Jbs. 
 0.5 
 
 days 
 34 
 
 gms. 
 
 2.84 
 
 gms. 
 1.13 
 
 days 
 32 
 
 gms. 
 3.14 
 
 gms. 
 1.18 
 
 1.5 
 
 89 
 
 1.25 
 
 0.56 
 
 61 
 
 2.45 
 
 0.76 
 
 2.5 
 
 122 
 
 0.96 
 
 0.43 
 
 75 
 
 2.48 
 
 0.64 
 
 3.5 
 
 158 
 
 0.76 
 
 0.34 
 
 99 
 
 1.22 
 
 0.52 
 
 4.5 
 
 197 
 
 0.52 
 
 0.28 
 
 122 
 
 0.95 
 
 0.43 
 
 5.5 
 
 250 
 
 0.23 
 
 0.21 
 
 148 
 
 0.68 
 
 0.36 
 
 ''The estimated protein retention was calculated by the use of Armsby's general- 
 ized equation given on page 378 of "The Nutrition of Farm Animals." 
 
 tein as computed from the Illinois analyses and growth data on White 
 Plymouth Rocks, and also from the growth data reported from Purdue, 
 appears in Table 40. The rate of gain of protein by growing White 
 Plymouth Rock cockerels is two to three times as rapid as that pre- 
 dicted from Armsby's equation deduced from data for larger farm ani- 
 mals. 
 
 A comparison of the rate of gain of energy by White Ply- 
 mouth Rock cockerels and by growing calves may be made using 
 Armsby's estimates of the rate of gain of energy per day and per 
 
 TABLE 41. ESTIMATED RATE OF GAIN OF ENERGY PER DAY PER POUND LIVE 
 
 WEIGHT OF WHITE PLYMOUTH ROCK COCKERELS AS COMPARED WITH 
 
 ARMSBY'S SIMILAR ESTIMATES FOR CALVES OF LIKE AGES 
 
 Illinois data 
 
 Energy retained daily per 
 pound live weight 
 
 Energy retained daily per 
 pound live weight 
 
 Age 
 
 Cockerels 
 
 Calves* 
 
 Age 
 
 Cockerels 
 
 Calves 8 
 
 days 
 34 
 89 
 122 
 158 
 197 
 250 
 
 cals. 
 21.0 
 10.6 
 9.0 
 
 7.8 
 5.8 
 2.8 
 
 cals. 
 17.4 
 11.1 
 8.9 
 7.1 
 5.6 
 5.0 
 
 days 
 32 
 61 
 75 
 99 
 122 
 148 
 
 cals. 
 23.2 
 20.7 
 23.4 
 12.5 
 10.5 
 8.0 
 
 cals. 
 17.6 
 13.4 
 12.2 
 10.4 
 8.9 
 7.6 
 
 Purdue data 
 
 "The estimates for calves were obtained by simple interpolation from Table 94, 
 page 402, of Armsby's "The Nutrition of Farm Animals." 
 
124 BULLETIN No. 278 [June, 
 
 1,000 pounds live weight by calves of different ages. 14 While Armsby 
 also estimates the rate of gain of energy by swine, his estimates can- 
 not be considered reliable, because of the small amount of data upon 
 which they are based and because of discrepancies existing among them. 
 In Table 41 the rate of gain of energy made by White Ply- 
 mouth Rock cockerels, per pound of live weight, at increasing ages, 
 is compared with Armsby's estimated rates of gain of energy by calves 
 per pound of live weight. The estimates for calves included in each 
 comparison have been obtained from Armsby's Table 94 by simple 
 interpolation. Except for the earliest and the latest age, a remark- 
 ably close agreement exists between the estimated rate of gain of en- 
 ergy of W T hite Plymouth Rock cockerels computed from the Illinois 
 growth data and the estimated rate of gain of energy by calves of 
 equal age. For the estimates based upon the Purdue growth data no 
 close agreement exists with Armsby's estimates at equal ages. 
 
 SUMMARY AND CONCLUSIONS 
 
 An investigation of the growth of White Plymouth Rock chick- 
 ens was made, involving observations of the increase in live weight, 
 the increase in body measurements, the increase in weight of individ- 
 ual organs and parts of the carcass, and the changing chemical compo- 
 sition of the carcass and of gains in weight with increase in size. 
 
 The growth and body weight of a flock of White Plymouth Rock 
 chickens numbering approximately 1,000 at the beginning of the ex- 
 periment was determined by weighing the birds individually every 
 two weeks. The growth of cockerels and pullets was observed sep- 
 arately as soon as the sex could be distinguished. When the cockerels 
 reached an age of 10 weeks, approximately half of them were capon- 
 ized, and from this time constituted a third group of birds. The rate 
 of growth as measured by the biweekly increase in body weight was 
 found to vary periodically. These variations, however, have not been 
 interpreted as representing true cycles of growth, because it is believed 
 that they more probably are related to periodical variations in en- 
 vironmental conditions, particularly variations in the weather. 
 
 Relative Growth of Cockerels, Capons, and Pullets. The growth 
 of the cockerels proceeded at a distinctly more rapid rate than that of 
 the pullets, even from the time when the separation was first made. 
 The rate of growth of the capons was not distinctly different from that 
 of the cockerels up to a weight of approximately 6 pounds. All groups 
 of birds grew at a much slower rate than the Purdue flock reported 
 upon in Bulletin 214 from that station. 
 
 From a study of the change in the ten body measurements with 
 advancing age, it appears that practically all of the measurements in- 
 creased in approximately the same proportion when referred to the 
 
THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 125 
 
 measurements of the .5-pound chicks. Thus, for the cockerels, all the 
 measurements except the length of middle toe increased approximately 
 two and a half times from the .5-pound to the 7-pound weight. This 
 would appear to mean that the conformation of the birds did not 
 change materially during the whole course of growth between these 
 two extreme weights. 
 
 At equal weights the pullets were, in general, smaller in external 
 measurement than the cockerels, the only measurement remaining ap- 
 proximately the same in the two sexes being the length of keel. The 
 leg measurements of the pullets in particular were appreciably smaller 
 than those of the cockerels of like weight, especially after a weight of 
 3 pounds was reached. 
 
 On the other hand, no distinct differences between the body meas- 
 urements of capons and cockerels at equal weights were revealed. 
 Castration apparently does not appreciably affect the body shape of 
 White Plymouth Rock cockerels. 
 
 Estimating Surface Area. The surface area of all birds slaugh- 
 tered in this experiment was directly determined by measuring the 
 area of the skin after removal from the carcass. In attempting to find 
 a formula by which the body surface of White Plymouth Rock chick- 
 ens could be estimated readily, it was found that the Meeh formula 
 could not be used over the entire range of weight from .5 to 7 pounds. 
 However, the Meeh formula may be applied with considerable accur- 
 acy to birds weighing more than 1 pound, using the value of 9.85 for 
 the constant, the area being expressed in square centimeters and the 
 weight in grams. A slightly more accurate formula, which may be 
 used for birds weighing from 1 to 7 pounds, inclusive, was devised by 
 the use of one of the body measurements, namely, the rump-to-shoulder 
 measurement, along with the body weight. This formula is as follows: 
 
 S = 5.86 W- 5 L- 
 
 in which S is the surface area in square centimeters, W, the weight in 
 grams, and L, the rump-to-shoulder distance in centimeters. This for- 
 mula also applies to Rhode Island Red chickens, but evidently does 
 not apply to White Leghorns unless the constant is made smaller (i.e., 
 5.03). 
 
 Growth of Different Parts of Carcass and Viscera. From a study 
 of the weights of the different organs and the different parts of the 
 carcass, it is evident that most of these increase in weight continuously 
 with advancing age. The digestive organs, however, are somewhat ex- 
 ceptional in their growth, since they reach their maximum size before 
 the bird has obtained its complete growth. 
 
 The offal part of the carcass, not including the inedible viscera, 
 was found to constitute a fairly constant percentage of the empty 
 weight of the birds at all weights, namely, very close to 19 per- 
 cent. This constancy in percentage weight holds particularly for the 
 blood weights. The percentage weight of blood is consistently higher 
 
126 BULLETIN No. 278 [June, 
 
 for the cockerels than for the pullets. The capons occupy an inter- 
 mediate position in this respect. 
 
 Following an initial increase from the .5-pound to the 1 -pound 
 chicks, the percentage weight of the total viscera showed a continuous 
 decrease with increasing weight of birds. This conforms with similar 
 data on man and other mammals. 
 
 The percentage weight of the total dressed carcass increased 
 slightly, but continuously, with increasing empty weight of the bird. 
 This relative increase in dressed carcass relates more to the muscular 
 tissue than to the bones. For all three groups of birds the percentage 
 weight of bone in the dressed carcass decreased with increasing body 
 weight, while the percentage weight of flesh and fat increased. 
 
 The total weights of offal were consistently less for the pullets 
 than for the cockerels of like weight. This is true of each item in the 
 offal, except the feathers. The weights of feathers for the pullets 
 were generally greater than those for the cockerels. While the total 
 weights of viscera did not differ greatly for cockerels and pullets, some 
 apparently significant differences existed between the two sexes rela- 
 tive to individual organs. For example, at a weight of 2 pounds the 
 lungs of the pullets weighed the same as the lungs of the cockerels, but 
 with increasing body weight the lungs of the cockerels weighed more 
 than those of the pullets, the differences increasing with increasing 
 body weight. Just the reverse is true with the kidneys. The weights 
 of spleen were consistently heavier for the pullets than for the cock- 
 erels. The dressed carcass in the pullets was always slightly heavier 
 than in the cockerels for body weights of 3 pounds or more, altho the 
 weights of bone in the dressed carcass were always greater at the 
 same body weight for cockerels than for pullets. In other words, the 
 edible flesh and fat always constituted a greater percentage of the 
 empty weight of the pullets than of the cockerels of equal weight. 
 
 Differences between cockerels and capons relative to the weights 
 of the different parts of the body were not so numerous nor so con- 
 sistent as those between cockerels and pullets. However, at a weight 
 of 7 pounds some interesting differences apparently existed. The 
 heart weights were distinctly greater for the cockerels than for the 
 capons at this weight, while the weights of liver, kidney, spleen, and 
 intestines for the capons were distinctly greater than for the cockerels. 
 The average weights of kidney and spleen were greater for the capons 
 than for the cockerels at all weights. Apparently castration pro- 
 foundly affected the growth of these visceral organs. 
 
 Chemical Composition of Birds. The data relating to the chemi- 
 cal composition of the birds showed the changes in dry matter, pro- 
 tein, ash, fat, and energy with increasing age that would be expected 
 from similar studies on other animals. Comparing the three groups 
 of birds, the analyses show that the pullets fattened distinctly more 
 
1926] THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 127 
 
 rapidly than the cockerels, while the capons occupied an intermediate 
 position. The energy values per gram of tissue for the pullets for 
 weights above 3 pounds were always distinctly higher than the energy 
 values for either cockerels or capons. The energy values of all samples 
 obtained in this experiment were directly determined by means of the 
 bomb calorimeter. 
 
 The distribution of nutrients between the three composite samples 
 analyzed in this experiment, namely, (1) the flesh and edible viscera, 
 (2) the bones of the dressed carcass, and (3) the head, shanks and 
 feet, blood, feathers, and non-edible viscera (conveniently referred to 
 as the offal), did not show any progressive changes with advancing 
 age. The flesh and edible viscera contained on an average 35.5 percent 
 of the total dry matter, 40.8 percent of the total protein, 30.2 percent 
 of the total fat, 37.2 percent of the total gross energy, and 14.7 per- 
 cent of the total ash of the entire carcass. 
 
 At equal live weights, pullets contained more edible fat and en- 
 ergy and as much edible protein as cockerels, the difference with re- 
 spect to fat and energy increasing rapidly with increasing live weight. 
 Capons, at equal weights, contained amounts of edible fat and energy 
 midway between cockerels and pullets, and smaller amounts of edible 
 protein than either. 
 
 From the analysis of these three composite samples the composi- 
 tion of the live birds at the different weights was computed, and from 
 these figures, the weights of chemical constituents contained in birds 
 weighing exactly 0.5, 1.0, 1.5, 2.0, 3.0 pounds, etc. To render more 
 accurate the subsequent calculations of the composition of successive 
 pound gains in weight, the experimental data on the composition of 
 birds at definite weights were smoothed out by fitting to them para- 
 bolic equations of the general type, 
 
 y =ax -\- bx 2 
 
 'the constants being determined by the method of least squares. From 
 the equations thus obtained the composition of birds at even pound 
 weights was estimated, and from these estimations the composition of 
 successive pound gains in weight was determined. 
 
 Rate of Retention of Nutrients During Growth. In computing 
 the daily retention of nutrients by birds of different ages, the data on 
 the corrected composition of successive gains and the data on the 
 growth and body weight of the entire flock of birds were used. 
 The latter were also smoothed out by mathematical means in a purely 
 empirical fashion. Since, however, the growth of the flock of birds 
 used in this experiment was considerably slower than the growth 
 of White Plymouth Rock chickens reported from the Purdue Ex- 
 periment Station by Philips, two sets of values on the daily reten- 
 tion of nutrients were computed, applying the values on the composi- 
 
128 BULLETIN No. 278 {June, 
 
 tion of successive gains to both the Illinois and the Purdue corrected 
 growth data. 
 
 The daily retention of protein by White Plymouth Rock cockerels 
 evidently ranges between 2 grams and 4.5 grams per day, depending 
 upon whether they are growing at their maximum rate or at a slower 
 and probably more nearly average rate for birds on the farm. Except 
 for smaller figures for the first two months of growth and a slowing 
 up of growth as maturity is approached, no marked change in the 
 daily retention of protein at increasing ages was noted. The daily 
 retention of protein by pullets and capons was less than that for cock- 
 erels. The daily retention of mineral matter by White Plymouth 
 Rock cockerels ranges between .2 gram and 1 gram per head, with no 
 clear progressive variation except for the early ages up to a weight of 
 2.5 pounds. The maximum retention of mineral matter was established 
 at a level of .5 to .8 gram daily. The daily retention of minerals by 
 pullets and capons appeared to be distinctly less than that by cock- 
 erels. 
 
 The estimates of the daily retention of energy by growing cock- 
 erels were quite variable at different ages, showing no progressive 
 changes after a weight of 2.5 pounds was reached. The average daily 
 rate of gain of energy from 2.5 pounds upward was about 25 calories 
 according to the Illinois growth data, and about 45 to 50 calories ac- 
 cording to the Purdue growth data. 
 
 Between pullets and cockerels no differences in the rate of reten- 
 tion of energy were apparent, tho for capons, the daily retention of 
 energy was consistently higher than for cockerels. 
 
 LITERATURE CITED 
 
 1. ARMSBY, H. P. The nutrition of farm animals, p. 400. Macmillan. 1917. 
 
 2. PURDUE AGR. EXP. STA. Bui. 214. 
 
 3. HOGAN, A. G., and SKOUBY, C. I. Journ. Agr. Res. 25, 419-430. 1923. 
 
 4. JACKSON, C. M. Amer. Journ. Anat. 15, 1. 1913-14. 
 
 5. DONALDSON, H. H. Amer. Jour. Physiol. 67, 1. 1923-24. 
 
 6. DONALDSON, H. H. Trans. 15th Internatl. Cong. Hyg. and Demog. Wash- 
 
 ington, D. C. 1912. 
 
 7. MARRASSINI, A., and LUCIANI, L. Arch. Ital. Biol. 56, 395. 1911-12. 
 
 8. HATAI, S. Anat. Rec. 9, 647. 1915. 
 
 9. HOSKINS, R. G. Amer. Jour. Physiol. 72, 324. 1925. 
 
 10. RICHTER, C. P. Johns Hopkins Hosp. Rpts. 36, 324. 1925. 
 
 11. KEMPSTER, H. L., and HENDERSON, E. W. Normal growth of domestic ani- 
 
 mals. Mo. Agr. Exp. Sta. Res. Bui. 62, 40. 1923. 
 
 12. ROBERTSON, T. B. The chemical basis of growth and senescence. Lippincott. 
 
 1923. 
 
 13. ARMSBY, H. P. The nutrition of farm animals, p. 378. Macmillan. 1917. 
 
 14. AUMSBY, H. P. The nutrition of farm animals, p. 402. Macmillan. 1917. 
 
1926] 
 
 THE GROWTH OF WHITE PLYMOUTH ROCK CHICKENS 
 
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