Tannin-Based Strategies for Mitigating Greenhouse Gas Emissions Through Nitrogen and Carbon Metabolism in Ruminants

Annual greenhouse gas emissions from livestock (CO2 equivalent) are estimated at approximately 7.1 billion tons, accounting for 14.5% of global emissions, with beef and dairy cattle production contributing 41% and 20% of total emissions, respectively. Greenhouse gases released by ruminants not only lead to feed energy loss but also result in environmental degradation. Therefore, reducing greenhouse gas emissions from ruminants is crucial for the sustainable development of the ruminant industry. The primary greenhouse gases produced by ruminants include nitrous oxide from ruminant manure storage and methane generated in the rumen via the action of methanogenic archaea. Tannins, a class of polyphenolic compounds present in many plants, play a significant role in animal feed. Recent studies have shown that incorporating certain tannins and their metabolic products into diets can modulate protein metabolism and the ruminal microbiome, thereby regulating greenhouse gas emissions from ruminants. This review summarizes the types and properties of dietary tannins, as well as the latest advancements in understanding the impacts of tannins and their metabolites on cattle nutrient digestion and greenhouse gas emissions, concluding that dietary tannin supplementation can reduce greenhouse gas emissions from ruminants. Future research should focus on identifying the optimal concentrations of different tannins and their metabolites in diets to minimize ruminant greenhouse gas production while maintaining animal performance and health.