Effects of Autolyzed Yeast Supplementation in a High-Starch Diet on Rumen Health, Apparent Digestibility, and Production Variables of Lactating Holstein Cows

SIMPLE SUMMARY: Feeding high-starch (HS) diets has negative implications on the ruminal health and milk production of dairy cattle. Autolyzed yeast (AY) supplementation may alleviate the negative effects of an HS diet fed to dairy cows. Therefore, the objectives of this study were to determine the effects of the supplementation of commercially available AY in HS diets on lactation performance, rumen pH, N utilization, apparent digestibility (AD), and blood metabolites in lactating Holstein cows. This study postulated that AY supplementation may improve the rumen environment (rumen pH and AD) when feeding HS diets, thus improving lactation performance and altering blood metabolites. ABSTRACT: Fifteen multiparous rumen-cannulated Holstein cows were assigned to one of five treatments in a replicated 5 × 5 Latin square design. The treatments were low-starch (LS) (22.8 ± 1% of dry matter; DM) without autolyzed yeast (AY; LS0, control), high-starch (HS) (31.2 ± 4% of DM) without AY (HS0), and HS with either 15 g (HS15), 30 g (HS30), or 45 g (HS45) of AY supplementation. Cows in HS0 had increased (p < 0.03) dry matter intake (DMI; 24.9 kg/d) and energy-corrected milk (ECM; 34.4 kg/d) compared to cows in LS0 (19.9 and 31.3 kg/d, respectively). There was a tendency for a quadratic treatment effect for feed efficiency (ECM/DMI, p = 0.07) and crude protein (CP) apparent digestibility (AD) (p = 0.09). Cows in HS45 tended (p = 0.09) to have increased DMI (25.6 kg/d) compared to cows in HS0 (24.9 kg/d). Cows in HS0 had greater (p < 0.04) milk protein nitrogen (N; 166 g/d) and microbial N production (161 g/d) than those in LS0 (140 and 138 g/d, respectively). In conclusion, the addition of AY tended to improve DMI, feed efficiency, and CP AD when cows were fed the HS diet.