Genomic predictions for greenhouse gas traits in Holstein cows

Genetic selection offers a sustainable approach to mitigating methane emissions from dairy cattle, a key contributor to agricultural GHG. This study evaluated 4 GHG-related traits, methane production (MetP, g/d), carbon dioxide production (CDP, g/d), methane intensity (MetI g/kg milk), and residual methane production (RMet, g/d) in Holstein cows. A total of 79,040 weekly averages of gas emission traits were available from 9,923 Holstein cows across 5 commercial herds in the United States. Moderate heritability estimates (0.16-0.28) were observed for all traits, indicating meaningful genetic variation and potential for selection. When 1 herd was excluded for validation, significant statistical differences in mean adjusted phenotypes were observed across GEBV quartile groups. Methane production and CDP exhibited unfavorable positive genetic correlations with production traits, suggesting that selection to reduce these traits may affect productivity. Methane intensity, although offering a practical measure of environmental efficiency, presents challenges for genetic evaluation due to the inherent complexity of ratio traits. Residual methane production displayed weaker genetic associations with other analyzed traits, highlighting its utility for targeted methane reduction with minimal impact on economically important traits. Despite international progress in developing GHG selection indices, large-scale and precise methane phenotyping remains a major bottleneck for fully integrating these traits into breeding programs. These findings support the inclusion of GHG-related traits in genomic evaluations and highlight the need for continued research and collaboration to enhance the sustainability and productivity of dairy cattle.