CHARACTERISTICS AND EFFECTS OF RUMINAL PROTEOLYSIS ON RUMINANT NUTRITION

To determine if amino acids are released equally during ruminal protein degradation, 4 hr ruminal in vitro degradation was determined on 10 proteins. Correcting for recovery of each amino acid, net release of 12 amino acids during protein degradation was calculated. Total release (molar percent of 12 amino acids studied) ranged from 8.6% for 60 min autoclaved CSM to 50.3% for casein. With all proteins, there were significant differences (P < .05) in mean releases of amino acids. Linear regressions, using the 10 proteins, indicated that there was a correlation in the extent release of each amino acid during protein degradation. The coefficient of determination (r('2)) for each amino acid was: lysine, .91; histidine, .93; arginine, .96; threonine, .86; glycine, .50; alanine, .95; valine, .97; methionine, .93; isoleucine, .96; leucine, .89; tyrosine, .92; phenylalanine, .94. The amino acids predicted to be degraded to a higher extent than total degradation were lysine, arginine, histidine, alanine and phenylalanine. Predicted degradations of threonine, glycine, valine, isoleucine, leucine, tyrosine and methionine were lower than total degradation.;Proteolytic activity of rumen microorganisms from the liquid fraction was compared to that from feed particle (FP) associated microorganisms. Microorganisms associated with FP were acquired by chilling (4C) or chilling in the presence of.1% Tween 80 before blending. Proteolytic activity tended to be larger from FP organisms treated with . 1% Tween 80 compared to chilling alone. Feed particle associated microorganisms from a steer consuming a concentrate diet had 28% of strained rumen liquor (SRL) activity. However, FP microorganisms from a steer consuming an all roughage diet had 72% of SRL activity.;Synthetic substrates were used to compare trypsin-like protease activity to chymotrypsin-like activity of ruminal microorganisms. Results using intact SRL organisms and protease extracts from microbial fractions indicate that trypsin-like protease activity is higher and more correlated to ruminal protein degradation than chymotrypsin-like protease activity.;Protein degradation by commercial proteases was compared to that by ruminal microorganisms. Enzyme solutions prepared from Streptomyces griseus (SG) protease and combination of SG and Bacillus amyloliquefaciens protease did not approximate ruminal protein degradation of five proteins (r('2) = .43 and .36). Papain and ficin proteases did not approximate ruminal protein degradation of nine proteins (r('2) = .43 and .38).