EFFECT OF INTRARUMINAL PROPIONIC-ACID INFUSION ON METABOLISM OF MESENTERIC-DRAINED AND PORTAL-DRAINED VISCERA IN GROWING STEERS FED A FORAGE DIET .2. AMMONIA, UREA, AMINO-ACIDS, AND PEPTIDES

This experiment investigated the effect of intraruminal infusion of pr opionic acid on the net flux of nitrogenous compounds across the mesen teric- (MDV) and portal-(PDV) drained viscera of seven Friesian steers , average BW 127 kg (SEM 4.6), fed a grass-pellet diet. Each received by random allocation 0 (control), .5, or 1.0 mol of propionic acid/d f or 7 d. Blood flow in mesenteric and portal veins was determined by do wnstream dilution of p-aminohippuric acid in order to determine net ap pearance rates across the gastrointestinal tissues. Net urea and ammon ia flux was unaffected by propionic acid supply. Circulating plasma fr ee amino acid concentrations were increased (P < .05) by propionic aci d infusion (2,235, 2,428, and 2,427, error mean square [EMS] 44,370 mu M, for control, .5, and 1.0 mol of propionic acid/d, respectively). N et amino acid flux rates were increased at the highest rate of propion ic acid infusion across MDV and PDV (4.66, 3.69, and 6.11, EMS 2.98 mo l/d for MDV [P < .05] and 2.98, 2.45, and 3.73, EMS 1.69 mol/d for PDV [P < .10] for control, .5, and 1.0 mol of propionic acid/d respective ly). Positive venous-arterio concentration differences for peptide-bou nd amino acids (PBAA) across the MDV and PDV indicated net appearance across the gastrointestinal tissues, but this was not affected by prop ionic acid infusion. The data show that amino acid flux across postrum inal tissues can be influenced by ruminal propionic acid supply and th at this does not affect PBAA appearance.