DETERMINATION OF RUMEN MICROBIAL-NITROGEN PRODUCTION IN SHEEP - A COMPARISON OF URINARY PURINE EXCRETION WITH METHODS USING N-15 AND PURINE-BASES AS MARKERS OF MICROBIAL-NITROGEN ENTERING THE DUODENUM

The present study compares estimates of rumen microbial-N production d erived from duodenal how measurements (N-15 and purine bases) with tho se from measurements of the urinary excretion of purine derivatives, F our Rasa Aragonesa elves fitted with simple cannulas in the rumen and proximal duodenum were used, Four diets consisting of 550 g lucerne (M edicago sativa) hay/d as sole feed or supplemented with 220, 400 and 5 50 g rolled barley grain/d were given in a 4 x 4 random factorial arra ngement, Duodenal digesta hows were determined by the dual-phase marke r technique during continuous intraruminal infusions of Co-EDTA and Yb -acetate, Microbial contribution to the non-NH, N (NAN) flow was estim ated from N-15 enrichment and purines:N ratio in duodenal digesta and bacterial fractions isolated from the rumen content, Whole tract organ ic matter (OM) digestibility and duodenal flow of OM and NAN increased (P < 0.001) with the level of barley supplementation. Digestible OM i ntake ranged from 19.0 to 42.7 g/kg metabolic weight (W-0.75) and the duodenal how of purine bases and the urinary excretion of allantoin in creased linearly (P < 0.001) from minimum values of 7.47 (SD 1.524) an d 4.65 (SD 0.705) mmol/d respectively on the basal diet to 18.20 (SD 1 .751) and 11.62 (SD 0.214) mmol/d on the 400 g barley diet; a further increase in barley supplementation decreased both variables (13.50 (SD 2.334) and 8.77 (SD 0.617) mmol/d respectively), Urinary excretion of uric acid and hypoxanthine showed a slight but significant increase ( P < 0.05) over all levels of barley, Molar recoveries of duodenal puri ne bases as purine derivatives or allantoin in the urine were 0.78 (SD 0.156) and 0.65 (SD 0.130) respectively, The increase on barley suppl ementation significantly augmented microbial-N, but large differences between microbial markers employed were observed, Mean values of micro bial-IV estimated from the duodenal purine bases or urinary allantoin excretion were on average 18 and 29 % lower than those measured by N-1 5.