Intestinal Digestion and Absorption of Protein

Amino acids in the protein of bacteria and undigested feeds that pass out of the rumen are digested by enzymes in the small intestine. As indicated earlier, the rumen bacteria contain an average of 10% N; 60% of this N is in protein that is digested and absorbed as amino acids in the intestines, 25% is in protein that is in bacterial cell wall and is excreted in the feces, and 15% is in nucleic acids that are absorbed and excreted in the urine.

The accuracy of prediction of amounts of amino acids in bacteria and feed digested in the intestines depends on the accuracy of prediction of ruminal flows, and therefore has second priority to the prediction of ruminal fermentation, particularly since, with most feeds, over 75% of total tract digestion occurs in the rumen.