CONTRIBUTION OF DIETARY NITROGEN AND PURINE-BASES TO THE DUODENAL DIGESTA - COMPARISON OF DUODENAL AND POLYESTER-BAG MEASUREMENTS

Four ewes jilted with ruminal and duodenal T-piece cannulas were given four diets in a 4 x 4 factorial design. Diets consisted of 700 (HF) o r 400 (LF) g/day of ammonia-treated barley straw supplemented respecti vely with 150 or 600 g/day of concentrate mane tip with barley plus ei ther soya-bean meal (SBM) or fish meal (FM) as the protein source, off ered at 2-h intervals. Duodenal flows of digesta were estimated by the dual-phase technique using Co-EDTA and Yb-acetate as markers and ((NH 4)-N-15)(2)SO4 was infused into the rumen to label microbial N. Bacter ia were isolated from the liquid (LAB) or solid (SAB) rumen digesta. P urine bases (PB) were isolated by precipitation in an acid solution of AgNO3, and microbial contribution either to the duodenal nitrogen (N) or PB were determined by N-15 measurements in duodenal digesta and ba cteria. Simultaneously, the rumen degradation of N and PB contained in SBM and FM was studied by incubating supplements in polyester bags in the rumen. PB content (mu mol/g dry matter) and guanine: adenine (G/A ) ratio of barley straw was 2.89 and 5.23; barley grain, 7.91 and 1.11 ; SBM, 18.8 and 1.26; and FM, 58.9 and 6.96, respectively. Duodenal fl ow of PB (mmol/day) was significantly higher than PB intake on all die ts and G/A ratio showed a mean value of 0.97, similar to the ratios de termined in SAB (0.80) and LAB (1.04) and much lower than diets (1.31 to 4.32). Microbial contribution to duodenal N flow ranged from 43.3% to 61.0%, being higher in SBM (59.0%) than in FM (46.7%) diets. Howeve r, microbial contribution to duodenal PB was not affected by the exper imental treatment, accounting for proportionately 0.77 of total PB at the duodenum. Rumen degradability of PB was much higher than that of t otal N and in both cases degradability was higher in SBM than FM. Dire ct measurements of non microbial N were significantly higher than valu es determined by the polyester-bag measurements. However, once correct ed for the endogenous N (52 mgN per kg live weight) contribution, resu lts showed an acceptable agreement. Duodenal flow of PB non-attributab le to microbes (unlabelled PB) showed a mean value of 3.25 mmol/day wi thout a significant effect of dietary treatment. However, undegradable PB supply determined for 0.02, 0.05 and 0.08 per h fractional outflow rates were proportionately lower than 0.025 with SBM and 0.100 with F M diets of the estimated duodenal PB flow. Despite the magnitude of th e unlabelled duodenal PB, the close agreement between G/A ratios in du odenal digesta and bacteria suggests that rite contribution of dietary PB to the duodenal flow was low and seems to confirm the reliability of values obtained from polyester-bag measurements.