ROLE OF BRANCHED-CHAIN AMINO-ACID INTRAVENOUS-INFUSION IN NITROGEN-UTILIZATION IN GROWING RUMINANTS

Investigations were made of the effects on nitrogen retention of conti nuous intravenous infusions of branched-chain amino acids (BCAA) with glucose. Eight wether lambs (35 kg) fed a full feed diet (2.68 Meal ME and 129 g CP kg(-1), DM basis) twice daily (50 g DM W-0.75 d(-1)) at a level of 1.2 times their maintenance energy requirement were continu ously infused intravenously (jugular) with L-leucine (Leu), L-isoleuci ne (Ile) and L-valine (Val). Infusion rates were 2.1, 1.5 and 1.7 g la mb(-1) d(-1), respectively, estimated to be about 50 % of that absorbe d from the gastrointestinal tract and / or required for muscle protein synthesis. Glycine was added to the infusion solutions to equalize th e total N infused. Glucose (12 g W kg(-0.75)d(-1)) was also supplement ed in the infusion solutions to maximise N-retention. Two 4 x 4 plus e xtra-period Latin squares were used. In square I, where the amino acid s were infused individually, the treatments were: control, Leu, Ile an d Val and in square II the treatments were: control, Leu, Leu + Ile an d Leu + Ile + Val. Each period lasted 6 days. Digestibility coefficien ts of DM and OM were 75.8 and 77.1 %, respectively, and were not affec ted by the treatment. Average N-digestibility was 67.1%; the Ile + Leu treatment increased N-digestibility (P<0.03) compared to control. Non e of the individually infused amino acids significantly altered urinar y-N (avg. 41% of total N-intake) or N-balance (avg. 22 % of total inta ke). In both squares, Leu alone failed to affect urinary-N or N-retent ion. Nitrogen balance was statistically (P<0.05) improved by 42%, when Leu was infused jointly with Ile. It is concluded that Leu infusion a lone does not affect N-utilization in growing lambs, but when Leu is c ombined with Ile, N-utilisation is improved. The infusion of Val had l ittle effect on N-utilization.