34 PROTEIN REQUIREMENTS OF CATTLE: MITCHELL 



The percentage composition of the gains is given for equal intervals of 

 age, in Table 18, and for equal intervals of body weight in Table 19. The 

 per cent " difference " in these tables and the absolute " difference " in 

 Tables 14 and 15 are accounted for by the " fill " of the cattle except for 

 errors in analysis or in mathematical estimation. Negative " differences " 

 in relation to gains may be interpreted as due to a decreasing fill. 



The significance of group differences in terms of growth and fatten- 

 ing. — The essential results of this investigation in so far as the question 

 of food requirements is concerned are contained in Tables 16 and 17, 

 i. e., the daily increments in nitrogen, ash and energy. These increments 

 must come from the day's food and represent those portions of the food 

 that are being used productively. For all three groups of steers, the daily 

 increments in these constituents decrease progressively after six months 

 of age, except the fat increment for Group I, which remains constant. 



Striking differences exist among the three groups of cattle in respect 

 to the amount of nutrients added to the body daily during growth and 

 fattening. These differences are greatest with respect to fat and energy, 

 and least with respect to water, nitrogen, and ash. It is important to 

 evaluate more precisely the significance of these group differences in 

 daily tissue increment occasioned by the imposed differences in the plane 

 of nutrition. 



According to the plan of the experiment. Group II represents more 

 nearly a normal growth of Hereford-Shorthorn steers, while Group I 

 represents an additional and considerable fattening and Group III a 

 retarded growth. In accordance with this plan. Group II eventually 

 attained a fat content of about 20 per cent. Group I a fat content of about 

 40 per cent, and Group III a fat content of about 13 per cent. It 

 would be interesting to compare the composition changes of these steers 

 with those of dairy heifers during normal growth, but this is impossible 

 to do directly in the absence of chemical analyses of the carcasses of 

 dairy heifers of different ages. 



In the absence of a direct method of comparison, an indirect one 

 must be resorted to. Brody and Eagsdale(**) have suggested a height- 

 weight relation as indicative of the state of nutrition of dairy heifers 

 differing in age. They point out that although the weight of growing 

 cattle is primarily dependent upon the plane of nutrition, the height at 

 withers is a remarkably good index of the growth attained and is not 

 readily affected by fattening. If weight is plotted against height, the 

 curve obtained for Jersey heifers follows very closely the curve obtained 

 for Holstein heifers, although a considerable age difference exists with 



