Saccharomyces cerevisiae fermentation products (SCFP) stabilize the ruminal microbiota of lactating dairy cows during periods of a depressed rumen pH

BACKGROUND: Effects of Saccharomyces cerevisiae fermentation products (SCFP) on rumen microbiota were determined in vitro and in vivo under a high and a depressed pH. The in vitro trial determined the effects of Original XPC and NutriTek (Diamond V, Cedar Rapids, IA) at doses of 1.67 and 2.33 g/L, respectively, on the abundances of rumen bacteria under a high pH (> 6.3) and a depressed pH (5.8–6.0) using quantitative PCR (qPCR). In the in vivo trial eight rumen-cannulated lactating dairy cows were used in a cross-over design. Cows were randomly assigned to SCFP treatments (Original XPC, Diamond V, Cedar Rapids, IA) or control (No SCFP) before two 5-week experimental periods. During the second period, SCFP treatments were reversed. Cows on the SCFP treatment were supplemented with 14 g/d of SCFP and 126 g/d of ground corn. Other cows received 140 g/d ground corn. During the first 4 wk. of each period, cows received a basal diet containing 153 g/kg of starch. During week 5 of both periods, the rumen pH was depressed by a SARA challenge. This included replacing 208 g/kg of the basal diet with pellets of ground wheat and barley, resulting in a diet that contained 222 g/kg DM of starch. Microbial communities in rumen liquid digesta were examined by pyrosequencing, qPCR, and shotgun metagenomics. RESULTS: During the in vitro experiment, XPC and NutriTek increased the relative abundances of Ruminococcus flavefaciens, and Fibrobacter succinogenes determined at both the high and the depressed pH, with NutriTek having the largest effect. The relative abundances of Prevotella brevis, R. flavefaciens, ciliate protozoa, and Bifidobacterium spp. were increased by XPC in vivo. Adverse impacts of the in vivo SARA challenge included reductions of the richness and diversity of the rumen microbial community, the abundances of Bacteroidetes and ciliate protozoa in the rumen as determined by pyrosequencing, and the predicted functionality of rumen microbiota as determined by shotgun metagenomics. These reductions were attenuated by XPC supplementation. CONCLUSIONS: The negative effects of grain-based SARA challenges on the composition and predicted functionality of rumen microbiota are attenuated by supplementation with SCFP.