Investigations on the influence of duodenal histidine infusion on nitrogenand amino acid turnover of growing German Holstein bulls

The effect of a continuous duodenal infusion of L-histidine (His) (8 g/d) o n the retention of nitrogen was investigated in two experiments (I, II), ea ch of which was carried out using two young bulls. In Exps. I and II, the a nimals (150- 250 kg BW) were fitted with a re-entrant cannula in the proxim al duodenum and were fed diets containing 125g CP/kg DM and 11.5 MJ ME/kg D M. A third experiment (III) using two young bulls (140-200kg BW) fitted wit h a simple T-cannula was carried out infusing 6g L-His. The animals were fe d a low protein diet (94g CP/kg DM and 11 MJ ME/kg DM). The study was done to End out whether or not L-His is the first limiting amino acid (AA) for g rowing ruminants. N retention was 28 and 31, 38 and 38, 22 and 24 g/d without L-His infusion and with L-His infusion for Exps. I, II and III, respectively. Both in the experiments with a standard protein supply (I, II) and in the experiment wi th reduced protein supply (III), no significant differences were found betw een periods with and without infusion of L-His. The utilisation of duodenal NAN varied between 39% and 50% and was also not significantly influenced b y the duodenal infusion of L-His. No significant effect was observed on the flow of AA into the duodenum. The faecal excretion of AA was also not sign ificantly influenced by the infusion of L-His. The utilisation of individua l amino acids as calculated by the ratio of retained AA to intestinal appar ently digested AA, didnot differ significantly following the duodenal infus ion of L-His. As expected, the utilisation of His decreased. Of the differe nt essential AA, L-His was the most utilised (80%) followed by Arg (72%), M et (60%), Leu (45%) and Lys (44%), during periods without supplementation o f L-His. It is concluded that the intestinal supply of L-His from the basal diet was sufficient for the potential growth level of animals under these experimen tal conditions. In all AA present at the proximal duodenum, L-His could hav e at first a limiting effect on the performance of growing young bulls with high body gain. Arg and Met, but not Lys, could be second or co-limiting A A.