Mitigation strategies for methane emissions in ruminant livestock: a comprehensive review of current approaches and future perspectives

Enteric methane emissions from ruminant livestock represent a major contributor to agricultural greenhouse gases and reflect an energetic inefficiency in ruminant metabolism. This review critically evaluates current mitigation strategies aimed at reducing CH₄ production in ruminants, with an emphasis on practical applicability, biological mechanisms, and integration into sustainable dairy production systems. Nutritional interventions, including tannins, saponins, essential oils, garlic compounds, seaweed (e.g., Asparagopsis), probiotics, and chemical inhibitors such as 3-nitrooxypropanol (3-NOP), have shown promise in reducing CH₄ emissions. These additives can alter rumen microbiota, fermentation patterns, and animal productivity, with some achieving CH₄ reductions of 30-50% in vitro. However, results vary depending on diet, dose, delivery matrix, and duration, and the long-term effects on productivity, nutrient utilization, and product quality remain underexplored. Biological strategies, such as archaeal-targeted vaccines, bacteriophage therapy, and microbiome engineering, remain largely experimental but represent promising future directions. Genetic selection for low-emission phenotypes and improved manure management are also explored as complementary approaches to reduce emissions. Integrated strategies combining dietary, genetic, and management interventions tailored to specific production systems are likely necessary to achieve meaningful, sustained reductions in ruminant CH₄ emissions. The use of tannins, for example, has been shown to reduce CH₄ emissions by up to 20%, although the effectiveness depends on the type and concentration of tannins used. Saponins have also been found to reduce CH₄ emissions, potentially by inhibiting protozoa and methanogenic archaea. Essential oils, such as those from garlic and onions, have been shown to have antimicrobial properties, reducing CH₄ emissions by up to 40%. Seaweed, particularly Asparagopsis, has been found to reduce CH₄ emissions by up to 80% in some studies, although the effectiveness depends on the dose and duration of feeding. Probiotics, such as certain strains of bacteria and yeast, have been shown to reduce CH₄ emissions by up to 10%, potentially by altering rumen fermentation patterns. Chemical inhibitors, such as 3-NOP, have been found to reduce CH₄ emissions by up to 30%, although the long-term effects on animal health and productivity are not well understood.