Potential of silage inoculants to mitigate methane production from the rumen: A systematic review.

Direct-fed microbials (DFM) have shown potential to reduce CH4 emissions, enhance feed efficiency, and improve energy utilization in the cow. Live microorganisms and prebiotics can alter the rumen microbiota composition, reducing CH4 production while supporting host metabolism and productivity. Microbial inoculants are widely used in silages fed comparatively cheaply to dairy cows, and they can also be classified in the category of DFMs.                                                                                     

The addition of silage microbial inoculants such as Lactobacillus casei, a member of the lactic acid bacteria (LAB) group, has been shown to enhance the fermentative process and silage nutritive value. LAB can also inhibit the growth of undesirable microorganisms such as clostridia and Enterobacter during silage fermentation and some studies have demonstrated the potential of microbial silage inoculants to also reduce CH4 production in vitro. In this systematic review by the authors cited, the aim was to investigate whether microbial silage inoculants could reduce CH4 formation from the rumen microbiome, both ex vivo and in vivo.

The literature search focused on studies reporting CH4 gas production both in vitro and in vivo. Of the 434 articles initially identified, only 10 met the quality criteria and were included in the analysis. Among the selected studies, nine measured CH4 production using in vitro assays, whereas one reported an in vivo trial. The majority of the experiments (70%) were conducted using cattle rumen samples, including the in vivo study involving cattle; the remainder of the experiments used rumen samples obtained from sheep. Ten bacterial species were used as inoculants across the selected studies.

Lactobacillus buchneri, used in combination with additives, achieved in vitro the highest CH4 reduction at 83%. Lactiplantibacillus plantarum also showed a significant reduction in CH4 output, achieving a 48% decrease. Overall, 80% of the reviewed studies reported a reduction in CH4 production following the application of silage microbial inoculants. These findings suggest that silage microbial inoculants hold promise as a strategy to mitigate CH4 emissions. However, the limited number of studies highlights the need for further research to confirm these results and explore wider applications.

The authors therefore proposed that in future studies, strains that achieve significant CH4 reductions in vitro should be tested as inoculants during the ensiling of high-quality forage as a silage substrate, followed by in vitro assays to evaluate their effectiveness, as forage quality plays a pivotal role in CH4 production. Factors such as NDF content and forage maturity substantially influence fermentation pathways and the acetate-to-propionate ratio in the rumen.