Effects of live yeast supplementation on mid-lactation dairy cows performances, milk composition, rumen digestion and plasma metabolites during hot season

Fifty-six Holstein cows (36 multiparous and 20 primiparous), that averaged 145 +/- 23 days postpartum, were used to investigate the supplementing of live yeast (LY) on productivity during hot summer conditions, from July until August 2010. Cows were fed a control diet with or without 4 g of LY (15x10(9) CFU/g) per cow daily during a five-week period. Cows were milked three times a day and milk yield was recorded daily. Milk samples were also taken weekly for milk composition analysis. Blood samples and rumen liquor samples were taken in two subsequent days during the last week of the experiment. Milk production, 3.5% fat-corrected milk, and DM intake were similar for cows fed on both diets. A greater milk fat percentage was observed for cows fed LY compared to the control (P<0.05). However, milk urea nitrogen concentration in cows fed LY was lower compared to the control (P<0.01). Cows fed LY had greater blood glucose compared to the control (P<0.01). Blood urea nitrogen was lower for cows fed LY compared to the control (P<0.05). Non-esterified fatty acids, -hydroxybutyrate (BHB), triglyceride, total protein, and total cholesterol were similar for both diets. The apparent digestibility of NDF was greater for cows fed LY compared to the control (P<0.05). Rumen parameters such as pH, N-NH3, and VFAs were also similar for both treatments. The present results suggested that feeding LY to mid-lactation Holstein cows during heat stress can increase diet cell wall digestibility and improve milk fat percentage.