Modulation of the rumen microbiome and metabolism in dairy cows by altering the concentrate feeding pattern and the inclusion of Saccharomyces cerevisiae yeast.

Dairy cattle are typically fed a total mixed ration (TMR), which is prepared in an automated mixer wagon. On-farm, effective TMR mixing can often be neglected due to lack of time or training. This leads to a disbalance of intake and potentially detrimental effects on health and production. Using dietary treatments to simulate this effect, this study determined the response of rumen metabolism and microbiome to different concentrate allocations in combination with a live Saccharomyces cerevisiae supplement (yeast supplementation, YS). The 4 × 4 Latin square design consisted of four dairy cows fitted with permanent rumen cannulae, which were fed a partial mixed ration with dietary concentrates (4 kg per cow per day) in an even or an uneven pattern of allocation (concentrate allocation, CA). YS was included in the TMR at a rate of 10 g per cow per day. Rumen metabolism was determined by measuring the pH, volatile fatty acids (VFAs), and ammonia nitrogen (NH3-N). The rumen microbial community was characterised using 16S rRNA gene amplicon sequencing. Both CA and YS had no effect (p > 0.05) on the dry matter intake, milk yield, or composition. CA did not affect the rumen NH3-N and VFA concentrations (p > 0.05). YS inclusion tended to increase the rumen pH (p = 0.088), acetate (p = 0.076), and valerate (p = 0.091). YS significantly increased the total VFA (p = 0.033) and propionate concentrations (p < 0.016). CA had little overall effect on the rumen microbiome beta diversity. However, there was a reduction in the relative abundance of a Prevotellaceae feature associated with an uneven pattern of CA. Bray-Curtis clustering of the microbiome was observed with YS (p = 0.002), driven by a decrease of Gammaproteobacteria and Prevotellaceae features and an increase of a Christensenellaceae feature (LDA > 2.0).