Invited review: Global census on the development and implementation of direct genetic selection for enteric methane emissions in dairy cattle

Enteric methane emissions from dairy cattle are a major contributor to agricultural greenhouse gas emissions and a priority target for climate change mitigation. Despite decades of research into nutritional and management interventions, few mitigation options offer reductions at scale. While nutritional and management interventions can deliver short-term reductions,genetic selection offers a long-lasting, cumulative, and global mitigation strategy. However, breeding for reduced enteric methane emissions presents scientific, technical, and policy challenges that differ from those associated with conventional production and functional traits. This review provides a global census of the current development and implementation of genetic strategies to reduce enteric methane emissions in dairy cattle. Information was collated through expert interviews, focus groups, and consultations with academic institutions, breeding organizations, and industry stakeholders from multiple countries. We synthesize global experience in methane phenotyping technologies, proxy traits, trait definitions, and genetic evaluation methodologies, highlighting their relative advantages and limitations across diverse production systems. Current approaches to incorporating methane into breeding objectives are reviewed, including direct methane breeding values, residual and intensity-based traits, and greenhouse gas-weighted selection indexes. The review further summarizes emerging international initiatives aimed at harmonizing phenotypes, sharing reference populations, and enabling multi-country genetic evaluations. Key constraints limiting wider adoption, such as phenotyping capacity, trait standardization, data sharing, and recognition of genetic gain within emissions accounting frameworks, are identified. Genetic selection for reduced enteric methane emissions is moving from concept to implementation in several countries. However, its global impact will depend on sustained international collaboration, robust validation of methane traits, and alignment between breeding objectives, industry incentives, and climate policy.