The impact of methane inhibitors on ruminants: A systematic review and meta-analysis

The impact of methane inhibitors on ruminant performance and rumen microbial community composition is unclear. The aim of this study was to summarize the effects of methane inhibitors on the performance of ruminants and the structure of rumen microbial communities. A total of 13,043 studies were retrieved from the Web of Science database. Ultimately, 256 studies containing the variables we needed were included. The data were further extracted and processed. The study revealed the negative effects of methane inhibitors on ruminants, which were reflected in the reduction of feed intake and digestibility in ruminants. Adding methane inhibitors reduced the acetate concentration in the rumen and increased the propionate content in the rumen. There was no significant change in the α-diversity of the rumen microbiome, whereas the β-diversity of rumen microbes was enhanced. The effects of methane inhibitor supplementation showed dose-dependent significant differences, particularly in modulating rumen fermentation parameters and the structure of the microbial community. Furthermore, when the total VFA in the rumen were below 96.98 mmol/L, or the acetate concentration was below 61.26 mmol/L, or the acetate-to-propionate ratio was below 3.86, the suppression of methane production was most effective. The addition of methane inhibitors has a positive effect on the performance of ruminants, particularly by improving the structure of the rumen microbiota. Additionally, VFA have a certain threshold effect on methane production. This provides a reference for the application and selection of methane inhibitors.