166 The Feeding of Anwtals 



grains. All these deductions are based upon the excess 

 of oxygen used by the animal when engaged in the work 

 of chewing and digestion, over that used when at rest. 

 It follows from these results that anything in the way of 

 growth or treatment of a fodder which tends to toughen 

 or harden the tissue reduces the net energy value. It 

 has long been believed, though perhaps not proved, that 

 grain foods are superior to coarse foods to an extent not 

 accounted for by the differences in digestibility, and if 

 this is a fact, it is explained in part by the unlike com- 

 position but is to some extent undoubtedly due to the 

 greater effort of chewing and digesting the fodders. 



If we wish to ascertain the comparative energy worth 

 of two unlike rations, it would obviously be incorrect to 

 multiply the total quantities of protein, carbohj^lrates 

 and fats in each by the unit heat values in order to 

 ascertain the relative energy gain to the animal body. 



To recapitulate, we may define avaUcible energy as 

 total energy minus that which is lost in the excreta and 

 in gases which escape, and net energy as available energy 

 minus the cost of digestion and of preparing the food for 

 use. Net energy is the balance of profit to the animal. 



ENERGY RELATIONS OF THE SEVERAL NUTRIENTS 



As has been pointed out, the animal body is the field 

 of numerous mechanical a(;tivities. What is the rela- 

 tion of the several nutrients to these manifestations of 

 vital energy is an interesting and in some ways an 

 intensely practical matter. For instance, has protein 

 a peculiar function in the maintenance of muscular 



