42 PROTEIN REQUIREMENTS OF CATTLE: MITCHELL 



of nitrogen for these animals than actually occurred. In this case, how- 

 ever, the animals were not over-fat, so that their nitrogen gains should 

 not stand in an abnormally low ratio to their body weights. 



The explanation of the discrepancy becomes evident when Armsby's 

 original publication is consulted. It is evident from the curve drawn 

 to illustrate the closeness of fit of the equation to the data, but more so 

 when estimates made from the equation are compared with the data 

 from which it was obtained, that the agreement is not good for animals 

 of 450 days of age or older, and in particular that for these later ages 



TABLE 22 



The Estimated Daily Gains of Nitrogen by the Missouri Steers of Groups I 



AND II at Different Body Weights, Compared with 



Armsby's Predicted Gains 



Group I Group II 



the equation would lead one to expect rates of gain of protein (nitrogen) 

 two or three times as rapid as actually occurred. 



It seems improbable that any such generalized relation between 

 gain in protein and age of animal as that assumed by Armsby should 

 exist. It is true that inequalities of weight are taken care of after a 

 fashion by expressing the daily gain in protein per unit of weight, but 

 inequalities in the growing period of different animals or in the character- 

 istics of the growth curve are not removed. The equation appears to 

 assume that the growing period of all farm animals is the same, and that 

 at the same age the growth processes are equally intense and equally near 



