RUMEN MICROBIAL-PRODUCTION ESTIMATED EITHER FROM URINARY PURINE DERIVATIVE EXCRETION OR FROM DIRECT MEASUREMENTS OF N-15 AND PURINE-BASES AS MICROBIAL MARKERS - EFFECT OF PROTEIN-SOURCE AND RUMEN BACTERIA ISOLATES

Four ewes fitted with ruminal and duodenal T-piece cannulae were each given six diets in a 6 x 4 factorial design. Diets or experimental tre atments consisted of two ratios of forage: concentrate (700 : 150 (LC) and 400 : 600 (HC)). Forage was ammonia-treated straw and the concent rate was formulated with barley supplemented with one of thr ee protei n sources: sunflower meal, soya-bean meal or fish meal. Duodenal flows ofdigesta were estimated by the drralphase technique using Co-EDTA an d Yb acetate as liquid and solid markers. Microbial nitrogen (N) was e stimated front the digesta flow of purine bases and N-15 enrichment us ing as reference samples, bacterial isolates from the liquid (LAB) or solid (SAB) phase of rumen digesta. Duodenal flow of purine bases (mmo l/day) was lower on LC (12.9) than HC (17.7) diets but ii? both treatm ents it teas depressed by fish meal (12.3) compared with either soya-b ean (17.3) or sunflower meal (16.3) as supplements (s.e. 1.13). Urinar y excretion of purine derivatives showed a similar trend, 8.6 v. 11.1 mmol/day in LC and HC respectively and 8.8 v. 10.4 and 10.5 mmol/day i n fish meal, soya-bean and sunflower meal diets (s.e. 0.56), respectiv ely. Variation in excretion of urinary purine derivatives was mainly a ssociated with digestible organic matter intake with an average untie of 1.7 (s.e. 0.11) mmol per 100 g digestible organic matter intake. Ir respective of the microbial marker used, microbial yield teas higher i n animals offered HC than in those offered LC and with soya-bean or su nflower meal compared with fish meal supplemented diets. The microbial purine bases/N (mmol/g) ratio varied between LAB (1.99, s.e. 0.092) a nd SAB (1.69, s.e. 0.071) isolates leading to different estimates of m icrobial-RT yield (g)from duodenal purine bases (7.76 (s.e. 2.84) v. 9 .13 (s.e. 3.24)), urinary excretion of allantoin (5.57 (s.e. 2.0) v. 6 .57 (s.e. 2.03)) or total purine derivatives (6.43 (s.e. 2.39) v. 7.56 (s.e. 2.77)). Urinary excretion of allantoin or total purine derivati ves provided consistently lower estimates of duodenal microbial-N than duodenal purine bases or N-15, although it closely reflected the patt ern observed in direct measurements.