Experimental data on the effects of Saccharomyces boulardii on rumen microbial metabolism are scarce. The aim of this study was to examine whether S. boulardii had an effect on parameters of rumen microbial metabolism at different dosages and whether the yeast would be suitable as a probiotic agent for ruminants. To test whether the potential positive effects of S. boulardii could be attributed to the yeast's viability or to its content of nutrients, living and autoclaved yeasts were tested simultaneously. For this purpose, incubation trials were carried out using the long-term rumen simulation technique. Living and autoclaved yeasts were added to fermentation vessels at a concentration of 0.5 or 1.5 g/d. The addition of living and autoclaved yeasts stimulated microbial metabolism, with no major differences between the treatments. It was concluded that ruminal microbes digested the supplied yeast of S. boulardii as an additional substrate and that S. boulardii, at least in ruminants, is utilized as a prebiotic rather than as a probiotic agent.

The objective of this study is to determine whether a yeast culture of Saccharomyces cerevisiae has an effect on parameters of ruminal fermentation and whether the potential positive effects of yeast culture are associated with the yeast's viability. For this purpose, live and autoclaved yeast cultures were tested simultaneously in the rumen simulation technique (Rusitec). Each fermentation vessel received daily 9 g of a basal diet consisting 5 g meadow hay and 4 g pelleted concentrate.Yeast preparations (1.5 g/day) were added with the feed. Compared to the control vessels, the pH of ruminal fl uid was signifi cantly (P<0.05) lower in the vessels supplemented with autoclaved yeast culture. Live yeast culture had no effect on the pH. Both yeast preparations resulted in a signifi cant increase (P<0.05) in NH 3 -N concentration, total and individual short-chain fatty acid (SCFA) production except valerate. The increase in NH 3 -N concentration and propionate production was signifi cantly higher (P<0.05) in the vessels supplemented with live yeast culture than that with autoclaved yeast culture. Also, the ratio of acetate to propionate was signifi cantly lower (P<0.05) by live yeast culture, when compared with the control vessels. Organic matter digestibility was not signifi cantly affected by both yeast preparations. In conclusion, these results indicated that the addition of live and autoclaved yeast cultures stimulated ruminal fermentation but this effect was more pronounced with live yeast culture.

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ABSTRACT:The objective of the present study was to investigate the effects of three different hydrolysed yeast products derived from Saccharomyces cerevisiae [hydrolysed whole yeast (HWY), less hydrolysed whole yeast (LHWY), and yeast cell wall (YCW)] on microbial fermentation characteristics using the rumen simulation technique (Rusitec) with three consecutive experiments. The Rusitec system consisted of six fermentation vessels. Each vessel received 5 g chopped meadow hay and 4 g concentrate (as-fed basis) daily for up to 22 days. Yeast products were added to the fermentation vessels at a concentration of 0.25 or 0.75 g/day. In most cases, ruminal microbial activity was stimulated by HWY and YCW, particularly at the 0.75 g/day level. HWY resulted in a decrease (P < 0.05) in ruminal pH and an increase (P < 0.05) in total short-chain fatty acid (SCFA), acetate, propionate and methane productions, and an increase in NH 3 -N concentration when compared with the control values. Ruminal pH was not altered, but total SCFA, acetate, propionate, butyrate, and methane productions as well as NH 3 -N concentration increased (P < 0.05) in response to YCW treatment. Digestibility of organic matter was not significantly affected by either HWY or YCW. The effects of LHWY on ruminal fermentation characteristics were negligible. These results indicate that degree of hydrolysation (low or high) and composition of yeasts (whole cell or cell wall) have remarkable effects on ruminal microbial activity in the Rusitec system.