Mechanistic actions of a yeast fermentation product on rumen microbiome of lactating dairy cows during subacute ruminal acidosis (SARA)

The effects of a Saccharomyces cerevisiae fermentation product (SCFP) on the composition and functionality of microbial communities in the rumen were determined in vitro and in vivo under normal and subacute ruminal acidosis (SARA) conditions. In the in-vivo trail eight rumen-cannulated lactating dairy cows were used in a cross-over design. During the first of the 5-week experimental period, cows were randomly assigned to treatment, i.e. SCFP (Original XPC, Diamond V, Cedar Rapids, IA) or control. During the second experimental period, treatments were reversed. Experimental periods were separated by a two-week wash out period. During each period, the 4 cows on the SCFP treatment were supplemented with 14 g/d of SCFP in 126 g of ground corn. The other four cows received 140 g ground corn only. During the first 4 wk of each experimental period, all cows received a basal total mixed ration. During week 5 of both experimental periods, a SARA challenge was conducted in all cows by replacing 208 g/kg of the basal diet with pellets of ground wheat and barley (50:50 on a weight basis). Bacterial communities in rumen liquid digesta, were examined by 454 pyrosequencing and real-time quantitative PCR, and their functionality was predicted using PICRUSt and shotgun metagenomics. Across diets, SCFP increased Prevotella brevis, Ruminococcus flavefaciens, ciliate protozoa, and Bifidobacterium spp. Several of the adverse impacts of the SARA challenge, including the reductions of the richness of diversity of the rumen microbiome, in the abundance of Bacteroidetes and in the population of ciliate protozoa were attenuated by SCFP. Several changes in the predicted functionality of the rumen microbiome due to SARA and considered adverse, were also reduced by SCFP. Our result shows that SCFP boosts beneficial rumen bacteria, which is of particulate importance during unfavourable conditions in the rumen, such as SARA. The impact of SCFP on the health and production of dairy cows of may, therefore, be mediated though its favourable effects on beneficial rumen microorganisms. Determination of the full impact of changes in the predicted functionality of the gut microbiota due to the SARA challenges and SCFP supplementation on the production and health of cows remain requires further study.