636 NUTRITION OF FARM ANIMALS 



(749). This is especially true of the energy of roughages, which 

 contain much indigestible matter, but even with the more di- 

 gestible materials the loss through the feces is relatively con- 

 siderable. With swine it is relatively less than with herbivora 

 because the former animals are usually largely fed on concen- 

 trates. The influence of various conditions upon the losses in 

 the feces, i.e,, upon digestibility, has already been discussed in 

 3 of the previous chapter. 



743. Losses in urine. The urine is especially the vehicle 

 for the removal from the body of the end products of protein 

 katabolism, of which urea is the most familiar and frequently 

 the most abundant. Numerous other nitrogenous substances, 

 however, are contained in the urine, particularly the purins and, 

 in herbivorous animals, hippuric acid. Moreover, as stated 

 in Chapter V (224, 225), the urine of herbivora in particular 

 may contain relatively considerable quantities of non-nitrog- 

 enous excretory products regarding the nature of which little 

 is known. All these substances carry off a portion of the gross 

 energy of the feed as unused chemical energy, the amount of 

 the loss being measured by their heats of combustion. That 

 the extent of these losses cannot be satisfactorily computed from 

 the nitrogen content of the urine has already been pointed out. 



The loss of chemical energy in the urine, as appears from 

 Table 187, constitutes a relatively small percentage of the 

 total loss. As would be expected, it is quite variable, being 

 higher as the feed supply is richer in protein, and lower with 

 relatively indigestible substances where the loss in the feces is 

 larger. 



744. Fermentation losses. The gaseous products, chiefly 

 methane, of the fermentation of the carbohydrates in the di- 

 gestive tract of herbivora, especially of ruminants, carry off con- 

 siderable amounts of unused chemical energy, one gram of 

 methane, for example, having a heat of combustion of 13.344 

 Calories. 



The extent to which the carbohydrates are attacked by the 

 methane fermentation appears to be somewhat variable. 

 Armsby and Fries x have observed that with cattle it is dis- 

 tinctly greater on light than on medium or heavy rations and 

 the same authors likewise observed a single instance of indi- 



1 Jour. Agr'l Research, 3 (1915), 445. 



