Potential use of Acacia mearnsii condensed tannins to reduce methane emissions and nitrogen excretion from grazing dairy cows

Summary

This study evaluated Acacia mearnsii condensed tannin (CT) supplementation in grazing dairy cows over two phases: a 5-week grazing study with 60 cows, followed by a 6-day metabolism study with 15 cows. High-dose CT (244–326 g d−1) reduced methane emissions by 29% and decreased urinary nitrogen excretion from 39% to 22% of feed nitrogen, but simultaneously reduced milk yield from 33.0 to 29.8 kg cow−1 d−1 and depressed energy digestibility. The authors conclude that whilst CT can mitigate enteric emissions and nitrogen losses from high-protein pastures, the magnitude of dose tested caused production penalties that limit practical application.

Regional applicability

The study used ryegrass pasture with high crude protein concentration typical of temperate dairy systems; findings are directly relevant to UK dairy farming. However, the authors note that CT doses tested were too high for practical adoption, suggesting that lower, optimised doses—yet to be determined—would be needed to make the intervention viable in UK grazing systems.

Key measures

Methane emissions (% reduction), milk yield (kg cow−1 d−1), milk fat and protein yield, fat and protein content, energy digestibility (%), urinary nitrogen excretion (% of feed N), feed intake

Outcomes reported

The study measured methane emissions, milk production and composition, energy digestibility, and nitrogen balance in lactating dairy cows supplemented with condensed tannins from Acacia mearnsii bark. Treatment effects on feed intake, energy partitioning, and urinary nitrogen excretion were quantified.

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