COMPARATIVE VALUE OF FEEDS. 33 



of hay, straw and the starchy matter of corn, wheat, etc., are much cheaper 

 per pound than protein. 



The animal needs mineral matter, especially for the building up of 

 bones, and there is some mineral matter in the muscles and all other portions 

 of the body. When animals are properly nurtured otherwise, the stock- 

 man need not consider the question of mineral matter in feeding stuffs be- 

 cause there will always be enough of these substances in the feeds he sup- 

 plies. Neither in this connection need we consider water, which is the 

 great vehicle of nutrition. 



When a cow consumes any given feed hay, for example, the process 

 of reducing it to infinitely fine particles begins with mastication; the hay, 

 moistened by saliva, is softened and passes into the paunch where it is still 

 further softened by moisture and heat. Re-chewed during rumination it is 

 swallowed again and finally passes into the true stomach. Here it is at- 

 tacked by fluids which tend to dissolve all of the softer and more useful 

 portions. Leaving the stomach, any undissolved portions of the food are 

 further attacked by the bile, the pancreatic fluid, and the intestinal juices. 

 These solvents reduce most of the feed to a condition where it can be util- 

 ized. The dissolved parts are absorbed and enter the blood. The portion 

 so absorbed is considered the digestible part of the feed. The undigested 

 part passes along the alimentary tract and is finally ejected. It has 

 never been properly within the body but only inside of the long convoluted 

 tube (stomach and intestines) passing through the body. The digestible 

 portion of the food taken up by the blood is the only part which is really 

 useful to the animal. Since all the food constituents are not digestible and 

 only the digested parts are useful, we have come to speak of "digestible pro- 

 tein," "digestible carbohydrates," and "digestible ether extract" (or fat) 

 of feeding stuffs. The chemist in his laboratory can find out how much 

 total protein, total carbohydrates and total fat any given feeding stuff con- 

 tains; he cannot tell us, however, by laboratory methods how much of each 

 of these is really available to the animal. To determine the digestible por- 

 tion he must conduct feeding tests directly with the animal itself. This is 

 done in the following manner: He first analyzes the feed and determines 

 the total quantity of each constituent in a given allowance of feed. This 

 feed is then fed to the animal under experiment and all of the solid 

 excrement resulting from it is saved and likewise analyzed. The 

 sum of the constituents appearing in the solid excrement is subtracted 

 from the sum of the constituents given in the feed supplied and the 

 difference is called the digestible portion. Thus, if a hundred pounds of 

 protein are fed to an animal and thirty pounds appear in the solid excrement, 

 then seventy pounds must have passed from the intestines into the blood, 

 and in this case we would say that seventy per cent, of the protein in 

 this feed is digestible. 



Digestion and utilization of feed are different things. Two animals 

 may digest a given feed equally well and yet give quite different returns 



