Effects of supplementing an active dry yeast product on rumen microbial community composition and on subsequent rumen fermentation of lactating cows in the mid-to-late lactation period.

The effects of supplementing feed of cows in mid-to-late lactation with an active yeast product (Actisaf Sc 47) were evaluated using 15 Holstein cows in a replicated 3 × 3 Latin square design. The animals were fed a mixed ration with 33% neutral detergent fiber, consisting of timothy hay (29.8%), a commercial concentrate (70.0%) and commercial calcium triphosphate (0.2%), twice daily to meet 105% of their energy requirement. Yeast supplement was set at 0, 5 and 10 g per day over 21-day periods, each of which consisted of 14 days for adaptation followed by 7 days of data collection. Milking performance, plasma metabolite parameters, rumen volatile fatty acids, lipopolysaccharide and microbial properties were measured. Although there were no significant differences in feeding and milking performance or blood parameters associated with supplementation, the acetate to propionate ratio in the rumen fluid tended to decrease (P = 0.08). The population of Bacteroidetes tended to be less prominent (P = 0.07) and the fibrolytic bacterium Fibrobacter significantly increased (P < 0.05) in the rumen fluid of the yeast 10 g group compared with that of the control. These data suggest that effects of supplementing live yeast to cows in mid-to-late lactation may be limited to microbial composition and fermentation characteristics in the rumen.