In non-ruminants, ingested feeds are first digested in the abomasum. However, the material entering the abomasum of a ruminant is made up primarily of unfermented feed particles, some end-products of microbial fermentation and microbes which grew in the rumen. The rumen provides a suitable environment with generous food supply for microbes to grow and reproduce. The VFA cross the rumen wall and become the major sources of energy to the cow. As ruminal microbes grow, they synthesize amino acids, the building blocks of proteins.
Bacteria can use ammonia or urea as nitrogen sources to build amino acids.
Without bacterial conversion, ammonia and urea would be useless to the cow. However, bacterial proteins synthesized in the rumen are digested in the small intestine and constitute the major source of amino acids for the cow. Absorption of VFA through the rumen wall. Production and expulsion through belching of as many as 1000 liters of gases per day. Enzymatic digestion of carbohydrates, proteins and lipids.