Dietary supplementation with live or autolyzed yeast: Effects on performance, nutrient digestibility, and ruminal fermentation in dairy cows

This study was conducted to evaluate the effects of live or autolyzed yeast supplementation on dairy cow performance and ruminal fermentation. Two experiments were conducted to evaluate performance, feed sorting, total-tract apparent digestibility of nutrients, purine derivatives excretion, N utilization, ruminal fermentation, and abundance of specific bacterial groups in the rumen. In Exp. 1, 39 Holstein cows (171 ± 40 d in milk and 32.6 ± 5.4 kg/d milk yield) were blocked according to parity, days in milk, and milk yield and randomly assigned to the following treatments: Control (CON); autolyzed yeast (AY) fed at 0.625 g/kg DM (Levabon, dsm-firmenich); or live yeast (LY) fed at 0.125 g/kg DM (Vistacell, AB Vista). Cows were submitted to a 2-wk adaptation period followed by a 9-wk trial. In Exp. 2, 8 ruminal cannulated Holstein cows (28.4 ± 4.0 kg/d milk yield and 216 ± 30 d in milk), of which 4 multiparous and 4 primiparous, were blocked according to parity and enrolled into a 4 × 4 Latin square experiment with 21 d-periods (the last 7 d for sampling). Cows within block were randomly assigned to treatments sequences: control (CON2); live yeast (LY) using the same product and dietary concentration as described in Exp. 1; or autolyzed yeast fed at 0.625 g/kg DM (AY) or 0.834 g/kg DM (AY2). In Exp. 1 and 2, nutrient intake and total-tract apparent digestibility were not affected by treatments. Sorting for long feed particles (>19 mm) tended to be greater in cows fed yeast supplements than CON in Exp.1. Efficiency of N conversion into milk N was increased when feeding yeast supplements in Exp. 1. 3.5% Fat-corrected milk yield tended to be greater in cows fed yeast supplements than CON. Feed efficiency was increased when yeast supplements were fed to cows in relation to CON in Exp. 1. In Exp. 2, yield of fat-corrected milk and fat were greater in cows fed yeast supplements compared with CON2. Uric acid concentration and output in urine were increased when feeding yeast supplements when compared with CON2. Neither ruminal pH nor total volatile fatty acids were influenced by treatments. The current study did not reveal treatment differences in ruminal abundance of Anaerovibrio lipolytica, genus Butyrivibrio, Fibrobacter succinogenes, Butyrivibrio proteoclasticus, or Streptococcus bovis. Yeast supplementation can increase feed efficiency without affecting nutrient intake and digestibility, ruminal volatile fatty acid concentration, or ruminal abundance of specific bacterial groups. Supplementing live or autolyzed yeast, regardless of the dose, resulted in similar performance.