Three rumen and duodenum fistulated dairy cows were used to determine the e
ffects of fat and methionine addition to soybean meal on rumen degradation
of crude protein: the amino acid pattern and the intestinal digestibility o
f undegraded residues. The addition of 10% and 25% fat resulted in lower DM
degradation after 8 and 24 h of incubation. Protein degradation was reduce
d by 10% fat addition at 8 and 24 h, while 25% fat addition considerably lo
wered crude protein disappearance after only 8 h of incubation. A 10% fat a
ddition increases the content of essential amino acids in the undegraded re
sidue vs. the control, while 25% fat addition only increases the concentrat
ion of lysine, histidine and arginine. Standard soybean meal has higher int
estinal dry-matter digestibility than fat-coated soybean, probably due to i
nterference between the lipid matrix and the enteric enzyme attack which, m
ost likely, does not affect the proteolytic enzymes, given the small differ
ences in intestinal nitrogen disappearance found among the different soybea
n types. (C) 1999 Elsevier Science B.V. All rights reserved.