Global Research Trends and the Association Between Feed Efficiency and Enteric Methane Emissions in Ruminants: A Bibliometric and Thematic Review.

Enteric methane emissions and feed efficiency are increasingly being investigated as complementary traits for improving the environmental sustainability and productivity of ruminant systems. This study conducted a bibliometric and thematic review of scientific literature published between 2016 and 2025 to characterize research trends and synthesize evidence on the association between feed efficiency and enteric methane emissions in ruminants. Publications retrieved from Scopus and Web of Science were analyzed using Bibliometrix and VOSviewer, including scientific production, collaboration networks, keyword co-occurrence, thematic evolution, and burst analyses. A total of 659 publications from 158 sources were identified, with an annual growth rate of 13.97% and 40.36% international co-authorship. Scientific production increased from 37 publications in 2016 to 120 in 2025. Thematic analyses revealed a transition from the characterization of feed-efficiency and methane traits toward integrated approaches involving methane mitigation, nutrient utilization, rumen microbiology, genomics, and precision phenotyping. Evidence indicates that improved feed efficiency can contribute to lower absolute methane emissions, particularly through reduced feed intake, but does not consistently imply lower methane production relative to feed intake or productive output. Feed efficiency and methane emissions should therefore be considered complementary rather than interchangeable traits when developing sustainable breeding, nutritional, and management strategies.