EFFECTS OF CONCENTRATES IN A HAY DIET ON THE CONTRIBUTION OF ANAEROBIC FUNGI, PROTOZOA AND BACTERIA TO NITROGEN IN RUMEN AND DUODENAL DIGESTA IN SHEEP

Two sheep, cannulated at the rumen and the duodenum, were given diets of chopped orchard grass hay (H) and 3 parts grass hay to 2 parts conc entrates (M). The the pools and flows of anaerobic fungi, protozoa, li quid-associated bacteria (LAB) and solids-associated bacteria (SAB) we re measured. The anaerobic fungi contributed only 11-35 g N/kg of the microbial-N in the rumen and 7-27 g N/kg of the microbial-N flowing to the duodenum. Inclusion of concentrates in the diet increased fungal zoospore counts and biomass and, in sheep 1, resulted in a more than f our-fold increase in rumen protozoal counts: the protozoal contributio n to its microbial N increased from 41 to 66% in the rumen and from 4 to 15% in duodenal flow. For sheep 2, there was an almost two-fold inc rease in protozoal counts and their contributions to its rumen and duo denal microbial N increased from, respectively, 35 to 57% and 7 to 9%. These changes were associated with a decrease in the yield of rumen m icrobial-N from 31 to 25 g/kg OM digested in the stomach for sheep 1 b ut an increase from 37 to 42 g/kg OM digested in the stomach for sheep 2. In addition, there were decreases in non-ammonia-N (NAN) flow to a nd digestion in the intestines of sheep 1 but increases in sheep 2, Pr otozoa obtained 40-58% of their N from bacteria. When diaminopimelic a cid was used as the marker, bacterial-N was overestimated in rumen dig esta and appeared to be underestimated in duodenal digesta. The ratio of duodenal NA(15)N to either rumen or duodenal LAB-N-15 underestimate d the contribution of microbial-N to duodenal NAN. The mean retention times (MRT) of protozoa were much longer than those of digesta particl es, reflecting protozoal sequestration in the rumen. On the hay diet, the apparent MRTs of LAB were the same as those for SAB and particles whereas, when concentrates were included in the diet, the MRTs of LAB were similar to those of solutes in sheep 2 and between those of solut es and particles in sheep 1; apparent MRTs of SAB were always similar to particle MRT. These results and the calculated generation times of LAB and SAB were consistent with the conclusion that, on the hay diet, LAB were probably SAB ''in transit'' between particles but, with the inclusion of concentrates, they were predominantly starch-utilizing or ganisms whose proliferation in the rumen of sheep 1 was limited by pre dation by its large protozoal population. Ammonia was produced in and absorbed from the omasum and the N-15-incorporation data were consiste nt with the growth of LAB in the omasum.