Rumen Microbiology

Vertebrates lack the ability to hydrolyse beta glycosidic bond of plant cellulose due to the lack of an enzyme celulase. Thus ruminants must completely depend upon the microbial flora, present in rumen or hindgut, so as to digest cellulose. 

Digestion of food in rumen is primarily carried out by the rumen microflora which contain dense populations of several species of bacteria, protozoa, sometimes yeasts and fungi. It is estimated that 1mm of rumen contains 10-50 billion bacteria, 1 million protozoa and several yeasts, fungi.

As the environment inside a rumen is anaerobic, most of these microbial species are obligate or facultative anaerobes which can decompose complex plant material such as cellulose, hemicellulose, starch, proteins. Hydrolysis of cellulose results in sugars which are further fermentated to acetate, lactate, propionate, butyrate, carbon dioxide and methane. During grazing, ruminants produce large amount of saliva. Estimates are within 100 to 150 litres of saliva per day for an adult cow.

The role of saliva is to provide ample fluid for rumen fermentation and as a buffering agent.

Rumen fermentation produces large amounts of organic acids and thus maintaining the appropriate pH of rumen fluids is a critical factor in rumen fermentation.