EFFECTS OF YEAST CULTURE SUPPLEMENT ON DIGESTION OF NUTRIENTS AND RUMEN FERMENTATION IN CATTLE FED ON GRASS-SILAGE BARLEY DIET

The effects of including yeast culture (Saccharomyces cerevisiae plus growth medium; 5 x 10(6) organisms/g) on the digestion of dietary cons tituents in the rumen and total digestive tract were studied in a pair of monozygote twin bulls. The animals were fitted with cannulae in th e rumen and in the proximal duodenum. A diet of grass silage, barley a nd rapeseed meal (445, 445 and 90 g/kg total dry matter (DM)) was fed, with and without addition of 10 g per day of yeast culture (YC), in t wo treatment sequences. The addition of YC had no effect on the mean v alues of rumen pH, ammonia N concentration or molar proportions of vol atile fatty acids. Also, the postprandial changes in rumen fermentatio n pattern were similar when the diet did and did not contain the YC su pplement. The peak concentration of lactic acid 1 h after feeding tend ed to be higher in cattle receiving the YC diet (13.9 v 6.0 mmol/l). A pparent digestibility of organic matter (OM) (mean 0.780) and the prop ortion of OM digestion occurring in the rumen (mean 0.603) were not af fected by YC. Likewise, there was no effect on rumen or total digestio n of cell wall carbohydrates, and the results for the degradation of h ay DM in the rumen and for particle-associated carboxymethylcellulase and xylanase activities indicated that YC had no effect on the rumen e nvironment that could affect fibre digestion. Supplemental yeast did n ot affect the rate of microbial N synthesis (28.0 and 28.6 g/kg OM app arently digested in the rumen). The results indicate that the addition of YC to the diet is not likely to improve the efficiency of digestio n and fermentation in the rumen of cattle given a diet based on grass silage and barley.