CASE STUDY: Effect of Supplemental Live Yeast on Yield of Milk and Milk Components in High-Producing Multiparous Holstein Cows

A well-managed, high-producing commercial dairy herd was used to test the effect of supplementing live yeast (4 g/d per cow) to lactating Holstein cow diets. When data from cows on study for > 4 wk were analyzed separately, milk yield was greater (P < 0.05) for cows fed live yeast (41.2 vs. 42.4 kg/d for control vs. live yeast, respectively), indicating that an adaptation period for the rumen system may be necessary once live yeast is added to the diet. Cows fed live yeast for > 4 wk produced more (P < 0.05) milk true protein (1.22 vs. 1.27 kg/d for control and live yeast, respectively). Overall milk yield during the complete 12-wk trial was not affected by live yeast supplementation. Live yeast supplementation had no effect (P > 0.10) on 3.5% FCM yield, milk fat percentage, yield of milk fat, or milk true protein percentage over the entire test period. Overall milk true protein yield tended (P = 0.11) to be higher with the addition of live yeast to the diet. Milk urea nitrogen (mg/dL) and SCC were not affected (P > 0.10) by treatment. Cows supplemented with live yeast produced milk with a higher percentage of lactose and solids-not-fat (P < 0.05). Live yeast increased milk yield and milk true protein yield after 4 wk of supplementation.