Effect of fat coating on rumen degradation and intestinal digestibility of soybean meal

Three rumen and duodenum fistulated dairy cows were used to determine the effects of fat and methionine addition to soybean meal on rumen degradation of crude protein, the amino acid pattern and the intestinal digestibility of undegraded residues. The addition of 10% and 25% fat resulted in lower DM degradation after 8 and 24 h of incubation. Protein degradation was reduced by 10% fat addition at 8 and 24 h, while 25% fat addition considerably lowered crude protein disappearance after only 8 h of incubation. A 10% fat addition increases the content of essential amino acids in the undegraded residue vs. the control, while 25% fat addition only increases the concentration of lysine, histidine and arginine. Standard soybean meal has higher intestinal dry-matter digestibility than fat-coated soybean, probably due to interference between the lipid matrix and the enteric enzyme attack which, most likely, does not affect the proteolytic enzymes, given the small differences in intestinal nitrogen disappearance found among the different soybean types.