EFFECTS OF A LIVE YEAST CULTURE AND ENZYMES ON IN-VITRO RUMINAL FERMENTATION AND MILK-PRODUCTION OF DAIRY-COWS

Live yeast culture (Saccharomyces cerevisiae) grew best on malt extrac t agar and required incubation under aerobic conditions to maximize th e number of viable cells. In sterile, anaerobic ruminal fluid that had been supplemented with malt extract, yeast cells remained viable and metabolically active for up to 48 h, as indicated by the production of ethanol. A supplement containing live yeast and enzymes was fed twice daily with a diet of 50:50 (wt/wt) forage to concentrate (dry matter basis) to continuous fel mentors inoculated with mixed ruminal microor ganisms. The supplement had no effect on major fermentation acids or p H. After the last supplement with yeast was fed, numbers of yeast imme diately decreased in the fermentors and were not detectable after 24 h . In the first of two lactation experiments, Holstein cows in midlacta tion were offered a diet with corn silage as the primary forage source . Half of the cows received a top-dressing based on corn that containe d 10 g/d of the yeast and enzyme supplement. The supplement had no eff ect on milk production, milk composition, or dry matter intake. In a s econd lactation experiment, high producing cows in early lactation wer e fed 0, 10, and 20 g/d of the supplement. Cows fed the control diet p roduced 36.4 kg of milk/d, and milk production was 39.3 and 38.0 kg/d from cows fed 10 and 20 g of yeast/d, respectively.