THE PRODUCTION VALUES OF FEEDING STUFFS 651 



754. Influence of feed consumption on metabolism. As 



is evident from i of Chapter VIII (365), the fact that the 

 consumption of feed tends to increase the heat production of an 

 animal has become a commonplace of physiology. The mag- 

 nitude of the effect varies within rather wide limits according 

 to the species of animal and the chemical and physical proper- 

 ties of the feed, while there is still more or less difference of 

 opinion as to its causes. Zuntz and his associates have called 

 it " work of digestion " and have attributed it largely to in- 

 creased muscular and glandular activity of the digestive and 

 excretory organs. Numerous investigations in this field have 

 been made on carnivora or on man, in which the increase of 

 the metabolism is not usually very large except when much pro- 

 tein is consumed. The more recent experiments on these species 

 appear to have shown that the mechanical work of the digestive 

 organs is but a small factor and that the term " work of di- 

 gestion " is not a fortunate one. With herbivora and especially 

 with ruminants, on the other hand, the total effect on the heat 

 production is quantitatively much more marked, and the 

 mechanical factor is of greater significance. 



755. Results on cattle. As illustrated in an earlier chapter 

 (364, 449) the effect of feed consumption upon the metabolism 

 of ruminants may be determined by comparing two periods in 

 which different amounts of the same feeding stuff or ration are 

 consumed, the increment of heat production on the heavier 

 ration being compared with the additional amount of feed con- 

 sumed. The experiments thus far reported have been almost 

 exclusively upon cattle, the principal ones being the pioneer 

 investigations of Kellner and Kohler 1 and the later ones of 

 Armsby and Fries. 2 



Most of Kellner and Kohler's experiments were made on super- 

 maintenance rations. The heat production was not measured directly, 

 but computed from the balance of carbon and nitrogen in the 

 manner indicated in Chapter VI (329), i.e., by indirect calorimetry. 

 Only a few of their results have as yet been published in full, but 

 from data regarding a few of the oth<y: experiments contained in 

 Kellner's book, the increments of heat production may be computed. 



. Vers. Stat., 47 (1896), 275; 50 (1898), 245; 53 (1900), 1-474. Die 

 Ernahrung der landwirtschaftlichen Nutztiere, 6th Ed., Berlin, 1912. 

 2 Jour. Agr. Research, 3 (1915), 435. 



