Studies on the stability of rumen metabolism in sheep and the effects of dietary addition of yeast culture

Literature concerning the use of feed additives for animal production were reviewed. Special emphasis was given to the use of probiotics in animal production and especially to the use of fungal probiotics in ruminants. The first experiment examined the ruminal responses to additional yeast culture (YC) and irradiated yeast culture (IYC). Six rumen fistulated wethers were randomly allocated to two 3 X 3 Latin squares. Both additives were found to alter the diurnal pattern of molar % propionate and ruminal ethanol concentration in comparison to the control diet. Supplementation with either YC or IYC did not affect diet organic matter digestibility (OMD), 24 hr. in sacco dry matter degradability (ISDMD), in vitro organic matter degradability (IVOMD), the efficiency of microbial protein synthesis (EMPS), or ruminal ammonia concentration, pH, and total volatile fatty acid concentration (t[VFA]). It was evident from the results of experiment 1 that substantial inherent daily variation existed in the rumen, as shown by the in sacco degradability measurements. Recovery of viable yeast from the rumen and faeces suggested that the viable yeast supplement had a limited ability to survive in the rumen and pass into the abomasum and intestines. A short in vitro experiment was then described which showed that the IYC supplement was not metabolically active, which indicated that the YC supplement may not need to be viable and metabolically active in order to induce a ruminal response. The method of urine collection for the determination of urinary purine derivatives was investigated and the results described in the third experimental chapter suggested that good hygiene and immediate sample freezing (-2