The effect of dietary inclusion of yeast culture on digestion in the sheep

ABSTRACT Six mature sheep, each fitted with a rumen cannula, were assigned to six diets in a 6 × 6 Latin-square design experiment to examine the effects of a yeast culture on ruminal metabolism, rumen liquid outflow rate, fibre digestion in the rumen and overall nutrient digestibility. The yeast culture (YC) was a commercial product composed of a yeast (Saccharomyces cerevisae) and the media on which it grew and dried so as to maintain its fermentative capacity. The six dietary treatments were three diets differing in hay dry matter (DM): concentrate DM ratio (90: 10, 65: 35 and 40: 60 designated low, medium and high concentrate respectively) each given either without or with a supplement of 4 g/day of YC. Treatment periods were of 3 weeks duration. There were significant effects of dietary forage: concentrate ratio on rumen function (P< 0·05). Rumen pH, rumen liquid outflow rate, rumen ammonia concentration, total volatile fatty acids concentration, and molar proportions of acetate, propionate and butyrate were not significantly affected by the inclusion of YC (P< 0·05). Supplemental YC did not affect the overall nutrient digestibility of organic matter, neutral-detergent fibre or gross energy measuredin vivo. However, at every forage:concentrate ratio, YC increased the disappearance of hay organic matter from nylon bags incubated in the rumen for 24 h (P< 0·05). The values with and without YC were 0·482 and 0·432 for the low, 0·423 and 0·366 for the medium, and 0·360 and 0·321 for the high concentrate diets respectively. However, YC had no effect on hay disappearance when bags were incubated for 48 h. YC appeared to increase the initial rate of forage digestion in the rumen without altering overall food digestibility or the patern of production of fermentation end products.