Impact of dietary supplementation of rumen native microbes on ruminal microbiome, ruminal fermentation,and total-tract digestibility in Holstein cows

Dairy cows were randomly assigned to receive one of three treatments consisting of rumen microbial additives. Treatments contained 100 g of corn meal containing no microbial additive (CON; n = 40), 100 g of corn meal containing 5 g of a mixture of 4 × 10,000,000 cfu of Clostridium beijerinckii and 1 × 1,000,000,000 cfu of Pichia kudriavzevii (G1; n = 38), or 100 g of corn meal containing 5 g of a mixture of 4 × 10,000,000 cfu of C. beijerinckii, 1 × 1,000,000,000 cfu of P. kudriavzevii, 1 × 100,000,000 cfu of Butyrivibrio fibrisolvens, and 1 × 100,000,000 cfu of Ruminococcus bovis (G2; n = 39). Rumen microbiome and diet digestibility were evaluated. Supplementation with microbial additives had subtle effects on the composition and diversity of the ruminal microbiota and total tract digestibility of nutrients. Cows fed microbial additives had increased total short-chain fatty acids concentration in ruminal fluid and partition of dietary N into milk N, but the effects were only observed in the first half of the experiment. The observed effects only partly explain improvements in the yield of milk or feed efficiency.