174 THE FEEDING OF ANIMALS 



The loss from the grains is relatively much less than 

 from the coarse fodders, being only an average of 31.5 

 per cent. This is easily accounted for by the greater 

 digestibility of the grains. 



We are to understand, then, that the metabolizable 

 energy of a ration is represented by the fuel value of the 

 dry matter which is digested from it, minus the dry mat- 

 ter of the urine and that lost in gases. 



If, however, we wish to know the actual energy gain 

 to the animal from a particular ration, we must go farther 

 than a determination of its available energy. 



255. Net energy. Within a comparatively short time 

 we have begun to speak of the net energy of foods, and as 

 this is a practical consideration which is likely to be the 

 subject of much future discussion, it is well to notice it 

 in an explanatory way. As we have learned, food is not 

 applied to use until it reaches the blood. Between the 

 time when it is taken into the mouth and when it passes 

 into the circulation, it must have work expended on it 

 in the way of mastication, solution, moving it along the 

 digestive tract and assimilation, and it seems probable 

 that the amount of this work for a pound of food must 

 vary greatly in different cases. In fact, this seemed to be 

 proven by the result of some masterly investigations con- 

 ducted by Zuntz and associates in Germany. 



256. Work of mastication (Zuntz), Zuntz determined 

 the oxygen consumption, that is, increased energy used, 

 during the mastication of several feeds by a horse as 

 compared with what occurred with the animal at rest. 

 In considering the data shown in Table XXXV it should 

 be remembered that mastication is only one factor of the 

 loss of energy involved in the appropriation of food, and 

 perhaps a minor one. 



