Synthesis of protein from non-protein nitrogen sources . Fermentative microbes can, for example, utilize urea to synthesize protein. In some situations, ruminants are fed urea as a inexpensive dietary supplement. They also secrete urea formed during protein metabolism into saliva, which flows into the rumen and serves as another nitrogen source for the microbes. Synthesis of B vitamins .
Mammals can synthesize only two of the B vitamins and require dietary sources of the others.
Fermentative microbes are able to synthesize all the B vitamins, and deficiency states are rarely encountered. Substrates for Fermentation With few exceptions, all dietary carbohydrates and proteins can serve as substrates for microbial fermentation. Nonetheless, the crucial advantage of being a herbivore is the ability to efficiently extract energy from cellulose and other components of plant cell walls. However, a variety of such beta-glucanases are synthesized by microbes. Thus, the diverse population of bacteria and protozoa in the rumen or hindgut produce all the enzymes necessary to digest cellulose and hemicellulose.