Effect of a viable yeast culture on digestibility and rumen fermentation in sheep fed different types of diets.

Five mature wethers fitted with rumen fistulas were fed grass hay and a sugarbeet-pulp-based concentrate or maize silage and a cereal-based concentrate (50/50 digestible organic matter basis), or without with 5 g yeast supplement (Saccharomyces cerevisiae, Biosaf) per day in a latin square design. Diets were given for a 28-d adaptation period, followed by a 10-d collection period to determine digestibility and nitrogen retention data. Afterwards, rumen samples were taken on 3 consecutive days and analysed for volatile fatty acids, pH and ammonia. Digestibility and nitrogen balance were not affected by yeast treatment. Supplementation of yeast increased acetate: propionate ratio, butyrate, isoacids, pH and ammonia. The effects were more pronounced for the maize silage diet. These results demonstrate that the effect of yeast culture on rumen fermentation may depend on the nature of the diet. Living yeast cell number in the rumen fluid rapidly declined when dietary yeast was ceased. Furthermore, yeast cells survived the passage through the digestive tract.