42 PRINCIPLES OF FEEDING FARM ANIMALS 



of the gastric juice, -pepsin, rennin, and gastric lipase, begin 

 to act. Pepsin, in acid solution, acts upon the proteins and 

 breaks some of them up into soluble substances known as 

 proteoses and peptones which, although they are still pro- 

 teins, are much less complex arrangements of amino acids. 

 Proteoses are formed in larger amounts than peptones by 

 p(^ptic digestion. Rennin curdles milk by the precipitation 

 of the casein. This prevents it from passing on through the 

 alimentary tract undigested. The casein then is acted upon 

 by the pepsin. Commercially, rennin is used in the manu- 

 facture of cheese. It is obtained from the stomachs of 

 young calves. 



The gastric juice also contains gastric lipase, an enzyme 

 ^\iii(']i sphts up emulsified fats into glycerin and fatty 

 acids. However, inasmuch as gastric lipase does not act 

 upon unemulsified fats, its practical value in digestion is 

 small. 



Soon after the feed reaches the stomach, the muscular 

 walls of the stomach begin a series of contractions, and the 

 more liquid portion of the feed is squeezed out into the 

 small intestine, while the more solid portion is retained for 

 fiu-ther action by the gastric juice. 



Stomach digestion in the ruminants or cud-chewing an- 

 imals differs from that in the horse and hog. When the 

 feed is swallowed by a ruminant, the coarser particles enter 

 the rumen, while the more liquid portion enters the reticulum, 

 and passes through the omasum, into the abomasum or true 

 stomach ; or the finely masticated food may enter the 

 omasum (hrectly from the esophagus. The coarser particles 

 may be returned from the rumen to the mouth and rechewed 

 at the will of the animal. While in the rumen the food is 



