PROTEIN REQUIREMENTS OF CATTLE: MITCHELL 43 



to completion. But Bro(ly(*^) has showai that it takes dairy cows from 

 81 to 93 months from conception to attain to 98 per cent of their mature 

 weight, Duroc-Jersey sows 67 months, and Suffolk ewes only 26 months. 

 For the Missouri Hereford-Shorthorn steers of Group II, it may be 

 shown from equation (3) that approximately 138 months from concep- 

 tion would be required for the attainment of 98 per cent of the estimated 

 mature weight of 1600 pounds. Any attempt to formulate a generalized 

 equation of the relation between the daily gain of protein per unit of 

 weight and the age of animals must evidently take account of such 

 specific differences in the time relations of growth. The use of equivalent 

 ages in Brody's sense, rather than absolute ages, may ultimately prove 

 successful in such an attempt. 



The Minnesota investigations on fattening steers. — Besides the Mis- 

 souri investigation of the changes in weight and composition of beef 

 steers during growth and fattening, there is available for this study the 

 extensive investigation of Haecker of the Minnesota Agricultural Experi- 

 ment Station (*^). This study involved a total of 63 steers, slaughtered 

 at approximately 100 pound intervals up to a weight of 1500 pounds. 

 From one to five animals were analyzed at each 100 pound weight. No 

 uniform method of feeding was employed, however: different groups of 

 animals were fed in the different years of the experiment on different 

 rations and no attempt was made to control the ratio of roughage to grain. 

 It appears from the following quotation that a very indefinite control of 

 the food consumption was practised : 



During all the feeding operations the intent was to provide the steers with 

 sufficient feed to satisfy the appetite, but not to provide more nutriment than 

 would be utilized. Each steer received as much hay and silage as he would eat, 

 and the amount of grain required was determined by the feeder. The chief 

 reliance in estimating the amount of grain needed was the odor given off from 

 the feces. Eating the ration quickly, restlessness, and looking for more indicated 

 a need of more feed; while slow feeding, failure to clean up the feed box, and 

 sluggishness indicated that less feed would suffice. 



The result of this ill-defined and unequal method of feeding the vari- 

 ous steers is reflected in the data secured. The age-weight relation, not 

 given in the Minnesota bulletin but secured from Missouri Research Bul- 

 letin 62, is quite abnormal in shape. There is no slowing up of the rate of 

 weight increase and all attempts to fit the data by the Brody growth 

 curve, which has been applied so successfully to a large number of animal 

 species, were unavailing. Starting out at a growth rate slightly less 

 than that of the Missouri steers of Group II, after ]2 months of feeding 

 they increased in weight at an increasingly faster rate, so that they 

 attained an average weight in 28 months that the Missouri steers attained 

 only after 44 months of feeding. 



