# The effect of fumaric acid on ruminant enteric methane emission and ruminal volatile fatty acids concentration: a meta-analysis

## TL;DR

Fumaric acid reduces methane emissions in small ruminants but has limited effect in cattle, without affecting their feed intake.

## Contribution

This study provides a meta-analysis showing fumaric acid's effectiveness in reducing methane emissions in small ruminants but not in cattle.

## Key findings

- FA supplementation significantly reduced methane production in small ruminants by 24.67%.
- Methane yield decreased by 1.954 g/kg dry matter intake in FA-supplemented animals.
- FA increased propionate concentration in the rumen but had no effect on acetate.

## Abstract

Methane emitted by ruminants represents an energy loss from feed intake and contributes to global warming. Fumaric acid (FA), a key intermediate in rumen metabolism, acts as an alternative electron acceptor and offers a potential strategy to reduce methane production. This meta-analysis systematically evaluated the effects of FA supplementation on enteric methane emissions and rumen fermentation in ruminants. Thirteen peer-reviewed studies met the inclusion criteria, contributing 22 effect sizes from 13 studies: six on cattle (dairy and beef cattle), seven on small ruminants (sheep and goats). Effect sizes were calculated as mean difference (MD) for methane yield (g/kg dry matter intake [DMI]), relative mean difference (RMD) for methane production (g/day) and DMI (kg/day), and standardized mean difference (SMD) for volatile fatty acids. A multilevel meta-analysis model was used to account for study-level variation. FA supplementation had no effect on DMI (P = 0.25; RMD = –2.75) but significantly reduced methane production (P = 0.005; RMD = –19.21). Meta-regression showed that increase in FA (g/kg DMI) decreases in methane production by 0.272% (P = 0.02). Methane production was significant in small ruminants (P = 0.002; RMD = –24.67) but not in cattle (P = 0.52; RMD = –7.03). The effectiveness of FA in reducing methane production was not (P > 0.05) affected by variations in dietary forage, concentrate, or neutral detergent fiber (NDF) content in FA-supplemented animals. Methane yield decreased (P = 0.001; MD = –1.954) in FA-supplemented animals, while the efficacy of FA was not influenced (P > 0.05) by diet composition (forage %, concentrate %, NDF %). FA had no effect on ruminal acetate (P = 0.49; SMD = –0.299), but increased propionate (P = 0.01; SMD = 0.970). In summary, FA supplementation did not affect DMI but reduced methane production and yield in small ruminants. While in cattle, FA supplementation may have limited impact on methane emission.

Fumaric acid supplementation reduces methane emissions in small ruminants (sheep and goat); however, FA supplementation is less effective in reducing methane emissions in cattle (beef and dairy).