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

Abstract This study explored the combined effects of vitamin B 12 and fumarate supplementation on methane (CH 4 ) 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 B 12 ), fumarate group (100 mg/g DM), and combined addition group (1 mg/g DM vitamin B 12 and 100 mg/g DM). All treatments had no effect on the dry matter degradation (DMD). Both vitamin B 12 and fumarate reduced CH 4 emission, increased the propionate concentration, and reduced the acetate/propionate ratio without any observed interaction. Vitamin B 12 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 B 12 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 CH 4 emission. In conclusion, the addition of vitamin B 12 and fumarate changed the fermentation mode of the rumen and reduced the emission of CH 4 by affecting the structure of the rumen microbial community, but no obvious interaction was found between the two.