Methane Emissions Regulated by Microbial Community Response to the Addition of Monensin and Fumarate in Different Substrates

Ruminants contribute significantly to global methane (CH4) emissions. This study aimed to evaluate the in vitro effects of monensin sodium salt (MSS) and disodium fumarate (DF) on CH4 production, rumen fermentation, and microbial community, with different substrates. The addition of MSS and DF, alone and in combination, significantly reduced the concentration and production of CH4 (p < 0.05), and while with vinasse as substrate, the CH4 production was higher for forage. The highest propionate production and lowest acetate and propionic ratio (A:P) values were all observed in cultures added to the combination of 14 mmol/L DF and 80 mg/kg MSS in both substrates, suggesting that these additives improved the rumen fermentation efficiency. The diversity indexes of prokaryotic microbiota with forage as the substrate were significantly higher than vinasse, and there were different effects on diversity indexes with the addition of MSS and DF depending on the incubated substrate. Supplementation with MSS and DF increased the number of starch degradation and fumarate reducing bacteria, decreased the number of methanogens, but had no significant effect on the number of fibrolytic bacteria. pH, NH3-N, and rumen volatile fatty acids (VFA) were the main factors influencing prokaryotic community structure. In conclusion, basal substrates (forage and vinasse) and CH4 mitigation additives (MSS and DF) have interactions on the in vitro rumen fermentation and microbial composition.