Breeding for a Greener Future: Selective Breeding and Crossbreeding Approaches to Minimize Methane Emissions in Ruminant Livestock

Methane emissions from ruminant livestock systems are a major contributor to agricultural greenhouse gases, intensifying global climate change. To mitigate these emissions, breeding strategies that reduce enteric methane output without compromising productivity must be developed. This review synthesizes the current research on the role of selective breeding and strategic crossbreeding in lowering methane emissions through enhanced feed conversion efficiency, rumen function, and incorporation of low-emission genotypes. The success of such breeding programs hinges on the precision of methane phenotyping techniques, including both direct (respiration chambers and tracer gas methods) and indirect (infrared sensors and milk or fecal biomarkers) measures, alongside the application of advanced quantitative genetic models, such as random regression and reaction norm models. The integration of genomic selection, high-throughput phenomics, and environmental covariates enables the identification of heritable variations in methane traits and facilitates genotype-by-environment interaction (GxE) modeling. Effective mitigation through genetic improvement requires a holistic understanding of the genetic architecture of methane production and its interactions with dietary, microbial, and management factors. Ultimately, incorporating both additive genetic effects and non-genetic influences into selection decisions can significantly accelerate progress toward low-emission ruminant populations with low methane emissions.