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. This study explored the effects of vitamin B12 and fumarate supplementation on CH4 emission and propionate synthesis in dairy cows through simulated rumen fermentation in vitro. Three Holstein cows were used as rumen fluid donors. The rumen fluid was taken and mixed with buffer solution in a ratio of 1:2. A total of 75 mL of inoculum was added to each fermentation bottle, which was then placed in a constant‐temperature incubator for 24 h of fermentation. In vitro fermentation experiments showed that metabolic hydrogen was transferred from methane production to propionate production. Supplementing vitamin B12 and fumarate increases the concentration of propionate, while reducing the concentration of acetate and methane emissions.