A 2024 Scientific Reports study compared purified tannin extracts from four forage species in 24-hour in-vitro rumen fermentation. This was not a long-term feeding trial in cattle.
The extracts came from birdsfoot trefoil, big trefoil, sulla and salad burnet and differed strongly in proanthocyanidin versus hydrolysable-tannin structure. They were added to perennial ryegrass substrate at 10, 20 and 30 g/kg dry matter.
Methane reductions came with different fermentation costs
Sulla and big-trefoil extracts reduced CH4 by up to 15% at 30 g/kg DM, but total gas production also fell by 11%, indicating reduced fermentation/digestibility.
Birdsfoot trefoil and salad burnet achieved methane reductions up to about 12% under conditions where total gas production was not significantly reduced. Chemical composition therefore mattered as much as dose. Added rutin did not provide a clear synergistic methane benefit.
In-vitro evidence is not a cattle-production result
Rumen fluid came from two cannulated heifers, but animals were not fed the experimental extracts while methane, milk/meat production and health were followed. High tannin doses can reduce digestibility, some hydrolysable tannins can be toxic, and rumen microbes may adapt over time.
Long-term in-vivo trials are required to optimize methane reduction together with intake, productivity and animal safety.
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Reference
- Verma S et al. Investigating the efficacy of purified tannin extracts from underutilized temperate forages in reducing enteric methane emissions in vitro. Scientific Reports. 2024;14:12578. https://doi.org/10.1038/s41598-024-63434-9
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