The forestomach of ruminants and large intestine of caudal fermenters are magnificent, continuous flow fermentation systems containing enormous numbers of microbes. Caudal fermentors cannot take advantage of this service, but in ruminants, bacteria and protozoa are constantly flowing into the abomasum and small intestine, where they are digested and absorbed. Fermentative microbes can synthesize all the amino acids and thereby provide them to their host. 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.