In the rumen, food undergoes mechanical and chemical breakdown. Mechanical breakdown results from thorough churning brought about by muscular contractions and aided by cornified surface of villi. Chemical breakdown is caused by symbiotic microorganisms (bacteria and ciliates) that release enzymes, cellulase, which act on cellulose and simplify it to short-chain fatty acids, such as acetic acid, butyric acid, propionic acid. This is called microbial digestion. The fatty acids are neutralized by sodium bicarbonate of saliva and are absorbed. These two processes reduce the hard plant food to a pulp.In the rumen, food undergoes mechanical and chemical breakdown. Mechanical breakdown results from thorough churning brought about by muscular contractions and aided by cornified surface of villi. Chemical breakdown is caused by symbiotic microorganisms (bacteria and ciliates) that release enzymes, cellulase, which act on cellulose and simplify it to short-chain fatty acids, such as acetic acid, butyric acid, propionic acid. This is called microbial digestion. The fatty acids are neutralized by sodium bicarbonate of saliva and are absorbed. These two processes reduce the hard plant food to a pulp.