Effects of Live Yeast Supplementation on Ruminal Parameters and Lactation Performance of Dairy Cows Fed Medium or High Levels of Dietary Concentrate

The objectives of this study were to determine the effect of live yeast (LY) supplementation and dietary concentrate level interaction on ruminal parameters, dry matter intake (DMI), milk yield, and milk composition of lactating dairy cows. Four multiparous Holstein cows were assigned to one of four dietary treatments in a 4x4 Latin Square design in a 2x2 factorial arrangement with 21-d periods The dietary treatments were:1) 50% concentrate + live yeast (10 g/cow/d; 50LY), 2) 50% concentrate + no live yeast (50NLY), 3) 70% concentrate + live yeast (10 g/cow/d; 70LY), and 4) 70% concentrate + no live yeast (70NLY). A more distinct effect of the LY supplementation on ruminal pH was observed at 9 h of post-feeding, where cows that received 70NLY had the lowest ruminal pH (5.81) compared to cows that received 70LY (6.40; P< 0.05). The LY supplementation decreased the sum of ruminal isobutyrate, isovalerate, and valerate concentrations (4.3 vs. 4.6 mol/100 mol and 4.7 vs. 4.8 mol/100 mol) in both 50 and 70% concentrate diets compared to NLY (P= 0.02). Overall, the LY supplementation had only numerically higher on DMI (18.0 vs. 17.5 kg/d), milk yield (20.2 vs. 19.1 kg/d), and 3.5% fat corrected milk (19.4 vs. 18.8 kg/d) compared to NLY supplementation, respectively. The LY supplementation tended to increase (P= 0.06) milk fat yield in 50LY (0.66 kg/d) compared to 50NLY (0.62 kg/d). Similarly, the LY supplementation tended to increase (P= 0.08) solid non-fat (SNF) percentage in 50LY (9.83%) compared to 50NLY (9.63%). Although there were only numerical increases in DMI, milk yield, and 3.5% fat corrected milk with the supplementation of the LY, results indicated that the LY supplementation in the 50% concentrate diet would increase milk protein, SNF, and lactose percentages. In conclusion, ruminal pH reductions associated with feeding high dietary concentrate (70%) diets in dairy cows can be prevented with the LY supplementation