430 ANIMAL BIOCHEMISTRY 



time of eating. The liquid, soluble, and finely divided portions of the 

 feed pass down the esophagus and through the esophageal canal 

 directly to the true stomach. The esophageal canal, which is a 

 continuation of the esophagus, is constructed somewhat like a rubber 

 hose cut lengthwise so that it can be opened. So long as the contents 

 are of a liquid nature, they pass through the tube, which remains 

 closed by muscular contraction. However, when large masses of fibrous 

 hay and similar materials are swallowed, the esophageal canal opens 

 and drops the coarse material into the capacious rumen. Here the 

 feed is brought into intimate contact with saliva and is fermented by 

 microorganisms. 



When tlie ruminant has completed feeding, it has the power to 

 regmgitate and masticate this coarse material at its leisure. This 

 process is known as "chewing the cud." From the rumen, the finely 

 comminuted food passes to the other stomachs or compartments and 

 eventually reaches the abomasum, where true digestion takes place. 

 During the rumination process, methane, acids, and alcohols are 

 formed in small amounts by fermentation. Certain members of the 

 vitamin B complex (thiamine, riboflavin, pyridoxine, and pantothenic 

 acid) are synthesized by the rumen organisms, which in addition partly 

 hydrolyze cellulose and hemicellulose, making these otherwise indi- 

 gestible materials available for subsequent assimilation by the animal. 

 Moreover, the symbiotic microorganisms also convert non-protein 

 forms of nitrogen like ammonia, urea, amino acids, piuines, pyrimi- 

 dines, and amides into the proteins making up the cells of their own 

 descendants. When the organisms pass along the digestive tract after 

 leaving the rumen, most of them die and the proteins undergo diges- 

 tion by the host animal. 



The microflora of the rumen consists of several species of bacteria 

 and some protozoa. The ecological aspects of the rumen are being 

 intensively studied in laboratory cultures and by sampling materials 

 from the rumen itself through a fistula established surgically. Al- 

 though the bacteria appear to play the major synthetic and hydrolytic 

 roles, the protozoa are important, at least in cellulose digestion. More- 

 over, they ingest bacteria and convert the protein of the latter (74 

 per cent digestible) to forms 91 per cent digestible by the host rumi- 

 nant, thereby adding to the efficiency of nitrogen utilization. 



Clearly the well-being of ruminants is contingent upon the main- 

 tenance of a suitable microflora so necessary for the riniien digestion 

 of polysaccharides. In part these microorganisms depend on a supply 

 of minerals some of which are ingested in the food. This source is 

 supplemented by the several ions of the saliva secreted copiously 



