Managing the rumen hydrogen economy to improve feed efficiency and climate-smart livestock production.

Enteric methane (CH₄) emissions from ruminant livestock present dual challenges for agricultural sustainability: contributing to greenhouse gas emissions while reducing feed conversion efficiency and animal productivity. Methane is produced by methanogenic archaea utilizing metabolic hydrogen (H₂) generated during ruminal fermentation. This hydrogen economy is central to fermentation efficiency, nutrient utilization, and methane formation. Conventional mitigation strategies have primarily focused on inhibiting methanogenesis; however, these approaches often yield inconsistent results across production systems and lack an integrative framework for systematic application. This narrative review proposes a shift in perspective from methane suppression to the management of H₂ flow within the rumen hydrogen economy and introduces two complementary conceptual frameworks to guide this approach. The genetic-microbiome co-evolution framework conceptualizes the rumen microbiome as a partially heritable trait shaped by host genetic and environmental selection, providing a theoretical basis for selecting low-emission, feed-efficient animals. The conceptual fermentation kinetics framework provides a mechanistic basis for understanding how dietary inputs and microbial interactions influence the distribution of hydrogen among competing metabolic pathways, including methanogenesis and propionate formation. Together, these frameworks establish a systems-level perspective that may inform the development of integrated strategies combining host genetic selection, precision nutrition, and microbial management. While substantial validation remains necessary, this approach provides a conceptual foundation for advancing methane mitigation from descriptive observation toward mechanistic interpretation, with the ultimate goal of supporting climate-smart livestock production systems.