THE PRODUCTION VALUES OF FEEDING STUFFS 635 



740. Gross energy. The energy supply of an animal is 

 contained in its feed as chemical energy, and the maximum 

 amount which any substance can furnish for the vital activities 

 by its oxidation in the body is measured by its heat of com- 

 bustion. This has been called its gross energy (315) to avoid 

 the implication that it represents the total amount of energy 

 associated with the substance. 



741. Losses of energy. It rarely, if ever, happens, how- 

 ever, that this maximum effect is realized. In practically every 

 case a larger or smaller proportion of the chemical energy of 

 the feed escapes unutilized. These losses of energy are of two 

 general classes. 



First, a portion of the chemical energy of the feed fails to be 

 transformed at all, leaving the body as chemical energy in the 

 visible excreta and in the combustible gases arising from gastric 

 and intestinal fermentations. 



Second, another portion of the chemical energy of the feed is 

 indeed transformed, but at ordinary temperatures virtually re- 

 sults merely in a superfluous heat production. It is true that 

 the metabolism consequent upon feed consumption is not only 

 unavoidable but may be regarded as a necessary expenditure of 

 energy for the support of the activities connected with digestion 

 and assimilation. Nevertheless, from the standpoint of the 

 net gain or loss by the organism this portion of the feed energy, 

 which ultimately takes the form of heat and escapes from the 

 body, must be regarded as a loss. 



The losses of chemical energy 



742. Losses in feces. Chemical energy escapes in the feces 

 both in the undigested feed residues which they contain and 

 in the excretory products which they carry. While the latter 

 portion is not derived immediately from the feed consumed, 

 but constitutes a loss of incompletely katabolized matter, it 

 must, none the less, be included in estimating the net effect 

 of a ration on the energy balance of the body. 



With herbivorous animals, the excretion in the feces con- 

 stitutes the greatest loss of chemical energy, and the one which 

 varies most as between different feeding stuffs or different species 

 of animals, as is apparent from the results recorded in Table 187 



