442 NUTRITION OF FARM ANIMALS 



animal so far as the percentage utilization of the energy supplied in 

 excess of the maintenance requirement was concerned, the slight 

 difference observed, especially in the earlier years, being perhaps 

 accounted for by the greater tendency of the pure-bred -steer to 

 lay on fat. 



In the aggregate a considerable number of breed tests of cattle, 

 sheep and swine have been made by the American experiment stations, 

 the results of some of which have been summarized by Henry 1 so as 

 to show the quantity of feed consumed per unit of gain. While in 

 individual cases considerable fluctuations are to be found, neverthe- 

 less, the results as a whole certainly fail to indicate any marked su- 

 periority of one breed over another in this respect, and later experi- 

 ments have not given materially different results. When we come to 

 consider the other possible factors, such as differences in live weight, 

 in maintenance requirement, in total feed consumed, etc., we must 

 conclude that the recorded results give no clear evidence of any 

 specific individual or breed differences in the actual physiological 

 processes involved in the conversion of feed into tissue, although it is 

 equally true, of course, that they fail to prove the absence of such 

 differences. 



It seems clear that it is necessary to look elsewhere than to 

 a supposed greater digestive and assimilative capacity of the 

 typical meat-producing animal for an explanation of his eco- 

 nomic superiority over the less specialized individual. 



517. The maintenance requirement. It was shown in 

 Chapter VIII (376, 391) that not inconsiderable differences 

 may exist between different individuals as regards the main- 

 tenance requirement. Thus in the case of cattle the extreme 

 figures of 4.72 Therms and 7.43 Therms of net energy per 1000 

 pounds live weight were observed for thin animals. Of the 

 various factors affecting the maintenance requirement, it was 

 pointed out that one of the most important is the degree of 

 muscular activity of the animal even when in the state of so- 

 called rest, and the decidedly lower maintenance requirement 

 found by Armsby and Fries for a pure-bred beef steer as com- 

 pared with a scrub was there interpreted as probably due to 

 the more nervous disposition and greater restlessness of the 

 latter. 



It is clear, however, that of two animals receiving identical 

 rations the one which has the lower maintenance requirement 



1 Feeds and Feeding, zoth Ed., pp. 328 and 511. 



