Combined effects of vitamin B12 and fumarate on rumen propionate production and methanogenesis in dairy cow in vitro

This study explored the combined effects of vitamin B₁₂ and fumarate supplementation on methane (CH₄) emission and propionate synthesis in dairy cows through simulated rumen fermentation in vitro. The experimental animals were 3 cows with an average milk yield of 23 ± 2.8 kg/d, a body weight of 618 ± 100 kg, and a parity of 3 ± 1 that were selected as rumen fluid donors. The TMR diet fed to cows is a fermentation substrate. Experiments adopted 2 × 2 factorial design, including control group, vitamin group (1 mg/g DM vitamin B₁₂), fumarate group (100 mg/g DM), and combined addition group (1 mg/g DM vitamin B₁₂ and 100 mg/g DM). All treatments had no effect on the dry matter degradation (DMD). Both vitamin B₁₂ and fumarate reduced CH₄ emission, increased the propionate concentration, and reduced the acetate/propionate ratio without any observed interaction. Vitamin B₁₂ made Prevotella and Prevotellaceae_ UCG-003 increase in quantity, and fumarate increased the abundance of Succinivibrionaceae_UCG-002 and Selenomonas, both of which are propionate-producing bacteria. At the species level, the supplementation of vitamin B₁₂ and fumarate slightly changed the abundance of some strains, but it was not statistically significant. Shifts in the abundance of propionate-producing bacteria and methanogenic archaea species suggest an increase in propionate production and a decrease in CH₄ emission. In conclusion, the addition of vitamin B₁₂ and fumarate changed the fermentation mode of the rumen and reduced the emission of CH₄ by affecting the structure of the rumen microbial community, but no obvious interaction was found between the two.