Effects of hydrolysed yeasts on ruminal fermentation in the rumen simulation technique (Rusitec)

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 NH3-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 NH3-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.