Impact of tannin-based additives on animal performance and enteric methane emissions in dairy and beef cattle: A meta-analysis

ABSTRACT This meta-analysis evaluated the effects of tannin-based feed additives on enteric methane (CH4) emissions, nutrient digestibility, and animal performance in beef and dairy cattle. A total of 23 peer-reviewed studies comprising 75 treatment means were included in the analysis. Random effects and mixed effects models were used to estimate relative mean differences and identify moderators of response. Robust variance estimation accounted for within-study dependence. Overall, tannin supplementation significantly reduced enteric CH4 emissions (−10.2%) and CH4 yield (−9.3%) across studies in beef and dairy cattle. Although no significant differences were detected between cattle types for CH4 emissions or yield, the database was unbalanced (14 beef vs. 9 dairy studies), and statistical support for a reduction in lactating dairy cows (7 studies) was weaker when analyzed separately (df = 1.7). These results warrant cautious interpretation for dairy systems. Likewise, no interactions between cattle type and tannin dose were detected for CH4 emissions or yield. The incomplete factorial representation of tannin types across cattle types further limited the evaluation of potential tannin type × cattle type interactions. No interaction between tannin type and dose was observed for enteric CH4 emissions or yield. Methane intensity in dairy (g/kg ECM) and beef cattle (g/kg average daily gain) was not affected by tannin supplementation, mainly due to differences in performance responses across studies. In dairy cattle, tannins had no significant effect on DM intake, milk yield, or milk composition. In beef cattle, tannins significantly decreased fiber digestibility by 9.8%, which was associated with reductions in enteric CH4 emissions. Ruminal fermentation parameters and pH were unaffected in both dairy and beef cattle. Meta-regression indicated that CH4 yield decreased by 1.0% per 1 g/kg DM increase in tannin dose. Effective mitigation generally required inclusion rates above ∼8,000 to 10,000 mg/kg DM, whereas subtherapeutic levels (4 emissions and yield highlight that the magnitude of tannin effects is likely driven more by bioactive properties than tannin type or dose. Future studies should quantify tannin bioactivity and evaluate its interaction with diet and rumen microbiota to enhance mitigation strategies.