Department of Animal Husbandry, University of Helsinki, SF-00710 Helsinki, Finland
The effects of including yeast culture (Saccharomyces cerevisiae plus growth medium; 5 x 106 organisms/g) on the digestion of dietary constituents in the rumen and total digestive tract were studied in a pair of monozygote twin bulls. The animals were fitted with cannulae in the rumen and in the proximal duodenum. A diet of grass silage, barley and 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 two treatment sequences. The addition of YC had no effect on the mean values of rumen pH, ammonia N concentration or molar proportions of volatile fatty acids. Also, the postprandial changes in rumen fermentation pattern were similar when the diet did and did not contain the YC supplement. The peak concentration of lactic acid 1 h after feeding tended to be higher in cattle receiving the YC diet (13.9 v 6.0 mmol/l). Apparent digestibility of organic matter (OM) (mean 0.780) and the proportion of OM digestion occurring in the rumen (mean 0.603) were not affected by YC. Likewise, there was no effect on rumen or total digestion of cell wall carbohydrates, and the results for the degradation of hay DM in the rumen and for particle-associated carboxymethylcellulase and xylanase activities indicated that YC had no effect on the rumen environment that could affect fibre digestion. Supplemental yeast did not affect the rate of microbial N synthesis (28.0 and 28.6 g/kg OM apparently digested in the rumen). The results indicate that the addition of YC to the diet is not likely to improve the efficiency of digestion and fermentation in the rumen of cattle given a diet based on grass silage and barley.
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