Live yeast culture (Saccharomyces cerevisiae) grew best on malt extract agar and required incubation under aerobic conditions to maximize the 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 fermentors inoculated with mixed ruminal microorganisms. The supplement had no effect on major fermentation acids or pH. After the last supplement with yeast was fed, numbers of yeast immediately decreased in the fermentors and were not detectable after 24 h. In the first of two lactation experiments, Holstein cows in midlactation were offered a diet with corn silage as the primary forage source. Half of the cows received a top-dressing based on corn that contained 10 g/d of the yeast and enzyme supplement. The supplement had no effect on milk production, milk composition, or dry matter intake. In a second lactation experiment, high producing cows in early lactation were fed 0, 10, and 20 g/d of the supplement. Cows fed the control diet produced 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.
Two experiments were conducted to evaluate the effect of microbial inoculation on the composition and nutritive value of corn silage for lactating cows. In Experiment 1, forage was untreated or treated at ensiling with Pioneer 1174 or Ecosyl silage inoculants. Forage was offered for free choice consumption, and concentrate was fed by a computerized feeder. Treatment with 1174 inoculant had little effect on silage composition and no effect on cow performance. Silage treated with Ecosyl inoculant had greater lactic acid content, but also greater acetic acid and ammonia N contents. Production of 3.5% FCM was greatest from cows fed silage treated with Ecosyl. In Experiment 2, silage was untreated or treated with Ecosyl and fed in a TMR. Inoculation had no effect on silage composition but increased 3.5% FCM production and DMI as length of time on treatment increased. Microbial inoculation can improve the nutritive value of corn silage for lactating cows even if changes in fermentation end products are minimal.
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