Dietary inclusion of Asparagopsis taxiformis significantly reduces methane emissions in dairy cows by mechanistically altering vitamin B12-dependent and other methanogenesis precursor pathways.
Lawther Katie K, Dimonaco Nicholas J NJ, Donnelly Paul P, Guinguina Abdulai A et al.
Ruminant products are widely consumed due to their high protein and micronutrient content, but ruminant production contributes significantly to greenhouse gas emissions, with methane (CH₄) accounting for 33% of anthropogenic emissions. CH₄ is generated via fermentative processes by the rumen microbiome, primarily through hydrogen utilisation by methanogenic archaea. Feeding beef cattle the red seaweed Asparagopsis taxiformis (ASP) has been shown to reduce CH₄ emissions by up to 80%. However, the microbial mechanisms underlying this reduction remain poorly understood. In this study, Nordic Red dairy cows (122 ± 13.7 days in milk) were fed grass silage and concentrate (60:40 dry matter basis) either with or without 0.5% ASP (organic matter basis) in a Latin square design, and rumen fluid was collected 19 days into each of the 3 experimental periods. ASP supplementation reduced CH₄ yield by 54% (g CH₄/kg DM). Metagenomic analysis revealed genes encoding pyruvate and propionate production pathways were more abundant in ASP treated animals, while those associated with acetate and CH₄ were reduced. Additionally, genes encoding vitamin B12 biosynthesis enzymes showed reduced abundances (e.g., adenosylcobinamide-GDP ribazoletransferase, EC 2.7.8.26, -29.92%). Vitamin B12 and its related cofactors are critical for methanogenic methyltransferases and C1 metabolism. Dominant taxa including Prevotella and Methanobrevibacter declined, while less abundant taxa increased their contribution to methane-related pathways, indicating niche displacement and community restructuring. CONCLUSION : ASP supplementation modulates the rumen microbiome through mechanisms extending beyond direct methanogen inhibition. The reduced abundance of genes involved in C1 metabolism and vitamin B12-dependent methanogenic processes suggest methane suppression is linked to broader restructuring of microbial metabolic networks. The redistribution of methane-related functions from dominant taxa to a wider taxonomic community indicates ecological reorganisation and functional resilience of the rumen microbiome. Collectively, these results reveal the multiple modes of action of ASP, establishing its promise as an effective methane mitigation strategy. Video Abstract.