Rumen Microorganisms

The rumen of a cow contains huge numbers of microorganisms that exist in a symbiotic relationship with the ruminant animal.  A ruminant must have microorganisms for digestion and fermentation to occur.  The microbes synthesize feed into available nutrients.  In turn, the microorganisms rely on the animal to maintain an environment with physiological conditions that allow survival (Yokoyama and Johnson, 1988).

A cow relies on many microorganisms present in the rumen to convert carbohydrates and cellulose into forms available for use by the animal (Ferguson, 1985).  The balance of microbes in the rumen undergoes constant adjustment in the ever-changing environment of the rumen.  There are three main types of microbes present in the rumen: bacteria, protozoa, and anaerobic fungi.

Factors affecting the balance of bacterial species in the rumen.  Adapted from Kistner, 1965.

Sixteen genera and 28 species of bacteria are thought to play an important role in digestion (Yokoyama and Johnson, 1988).  These bacteria perform jobs such as degrading starches, forming ammonia from amino acids, and metabolizing lipids, whereas the protozoa ingest particles of feed and degrade the major parts of the plants.  Protozoa also help to maintain the proper balance of bacteria by ingesting bacteraia as a source of protein (Yokoyama and Johnson, 1988).

Microorganisms serve many purposes: Synthesize proteins so that the cow does not need to get protein from its diet (Owens and Zinn, 1988). Use urea for protein synthesis (Houpt, 1959). Produce VFAs as source of C for metabolism Synthesize B vitamins and vitamin K (Huber, 1988). Reduce sulfate to sulfide as source for biosynthetic processes (Allison, 1965).