RELATIVE VALUES OF FEEDING STUFFS 621 



iments (162) showed that the increase in the nitrogenous ex- 

 cretory products in the feces was about the same whether the 

 added digestible matter consisted of carbohydrates or of protein. 

 Consequently, the addition of protein to a ration would tend 

 to diminish the apparent digestibility of the protein just as 

 would the addition of carbohydrates. 



The non-proteins, especially when given in the form of green 

 vegetable material and roots, likewise increase the nitrogen con- 

 tent of the feces, but a review of the literature of the subject l 

 shows that, as in the case of the proteins, the increase consists, 

 at least in large part, of metabolic products and does not indicate 

 any decrease in the true digestibility of the protein, although 

 it does, of course, decrease the amount available to the organism. 



726. Cause of diminished digestibility of carbohydrates. 

 The depression of digestibility of the non-nitrogenous ingredi- 

 ents of the feed of ruminants appears to be due to an entirely 

 different cause, viz., to a modification in the fermentation pro- 

 cesses in the rumen, and the fact that these effects are observed 

 chiefly on this class of animals lends strong support to this view. 



It has already been stated (128-132) that the disappearance 

 of more or less of the comparatively insoluble carbohydrates of 

 the feed during its passage through the alimentary tract is due, 

 particularly in ruminants, to a bacterial fermentation, occur- 

 ring principally in the first stomach and yielding chiefly carbon 

 dioxid, methane and organic acids. Furthermore, it has been 

 shown that when the more soluble carbohydrates, like starch 

 and sugar, are introduced into the ration they are attacked by 

 the organisms and undergo the same fermentation, yielding cor- 

 responding amounts of the characteristic gaseous product, 

 methane. It can scarcely be doubted that the decreased di- 

 gestibility of the less soluble carbohydrates under these cir- 

 cumstances is due to a partial diversion of the activity of the 

 ferment organisms to the maltose resulting from the action of 

 the saliva on the starch or to the sugar directly added, since 

 these substances are presumably more readily attacked than 

 cellulose and the like. 



The action of nitrogenous substances in counteracting this 

 effect of an excess of readily soluble carbohydrates is plausi- 

 bly explained as due to its supplying more nitrogenous food 



1 Compare U. S. Dept. of Agr., Bur. Anim. Indus., Bui. 139. 



