A meta-analysis of dietary inhibitors for reducing methane emissions via modulating rumen microbiota in ruminants.

Abstract

Background: Rumen methane emissions (RME) significantly contribute to global greenhouse gas emissions, underscoring the essentials to identify effective inhibitors for RME mitigation. Despite various inhibitors shown potential in reducing RME by modulating rumen microbes, their impacts include considerable variations and inconsistency.

Objective: We aimed to quantitively assess the impacts of various methane inhibitors on RME, rumen microbial abundance and fermentation in ruminants. Additionally, the relationships between microbial abundance and RME were also examined through the meta-regressions.

Methods: Meta-analysis and meta-regression were conducted to assess the impacts of methane inhibitions, including 3-nitrooxypropanol, ionophores, nitrate, triglycerides, phytochemicals and co-inhibitors, on RME and rumen microbiota in beef, dairy cattle and sheep.

Results: Analyses of 922 datasets from 274 experiments revealed that inhibitors, except ionophores (P = 0.43), significantly reduced RME, with co-inhibitors displaying the highest efficacy (SMD -2.1, P < 0.01). Inhibitors effects were more pronounced in sheep relative to beef and dairy cattle. Inhibitors decreased the abundance of ciliates and methanogens, with positive correlations observed between Dasytrichidae (P = 0.05), Entodinomorphs (P ≤ 0.001), Methanobacteriale (P = 0.001) and fungi (P < 0.01) with RME. Among inhibitors, triglycerides exhibited simultaneous reduction in methanogen, ciliate and fungal abundances. 3-nitrooxypropanol and triglycerides increased H₂ in the rumen while reducing the acetate-propionate ratio, especially in beef. The H₂ emission negatively (P < 0.01), and acetate-propionate ratio positively (P < 0.001) were correlated with RME, respectively.

Conclusions: Microbes including Dasytrichidae, Entodinomorphs, Methanobacteriale and fungi significantly attribute to RME, and co-inhibitors have the highest efficiacy in limiting RME and reducing microbial abundances. This study underscores the roles of both host and microbiota in modulating the inhibitor efficacy in RME, informing the refinement of rumen additives to mitigate RME from meat and milk production.