RESUMO
This study was conducted to compare nutrient digestibility, performance and immune response of dairy cows received live and autolyzed yeast during the transition period in high ambient temperature. Cows (n = 25) were randomly divided and received a basal diet with or without live yeast or autolyzed yeast as on top three weeks pre-parturition until three weeks post-parturition. The Control group received a basal diet without yeast products; other groups received 0.5 g live yeast; 1.0 g live yeast; 10 g autolyzed yeast and 20 g/d/head autolyzed yeast. Live yeast resulted in higher nutrient digestibility compared with autolyzed yeast and the control. Methane production was the highest in autolyzed yeast and the lowest in live yeast. Average milk production was the highest in cows that received live yeast. The highest IgG level was for cows that received autolyzed yeast at a dose of 20 g/d/head. Live yeast had no significant effect, but autolyzed yeast increased the relative expression of γ-Interferon and interleukin-2 as compared with the control group. It was concluded that live yeast at a dose of 1.0 g/d/head could influence ruminal fermentation and milk production, but autolyzed yeast at a dose of 20 g/d/head could influence the immune response of dairy cows during the transition period and heat stress.