Genetic correlations between enteric methane and traits of economic importance in a beef finishing system.

With the pressing global challenge of climate change, the potential to breed cattle that produce less lifetime methane offers a transformative solution that is both sustainable and impactful. The objective of this study was to determine the genetic correlations between enteric methane emissions and economically important traits included in the current terminal index used to breed animals for meat in Ireland. This terminal index is typical of terminal-type indexes used globally, constituting traits associated with calving performance, carcass merit, and efficiency traits such as feed intake and age at finish, as well as some ancillary traits such as docility. Methane and carbon dioxide flux measurements recorded from 2018 to 2024 using 10 GreenFeed Emission Monitoring systems in a progeny performance test center on 1,835 beef animals and a more expansive dataset from commercial farmers with phenotypic performance data on calving performance, carcass quality, and efficiency traits were available on up to 402,039 animals for analyses. Five trait definitions for methane and carbon dioxide emissions were derived: individual spot measures, 1-d, 5-d, and 10-d averages of spot measures, and a full test average per animal, where all emission measurements were averaged across the test period. (Co)variance components between all trait definitions and phenotypic performance traits were estimated using animal linear mixed models. Methane emissions were strongly correlated with feed intake ranging from 0.49 (standard error [SE] = 0.119) to 0.76 (SE = 0.057) and carcass weight ranging from 0.44 (SE = 0.050) to 0.50 (SE = 0.060) across trait definitions, suggesting that selection for reduced methane emissions could adversely impact growth and performance. An antagonistic correlation was found between methane and age at finish ranging -0.27 (SE = 0.063) to -0.18 (SE = 0.084), which suggests that animals who have an earlier finishing age produce more methane per day. Carcass conformation was positively weakly correlated with methane (0.09 to 0.12), thus suggesting there is a potential to select for improved carcass conformation with minimal impact on enteric methane emissions. Overall, these findings emphasize the need for breeding strategies that capture the trade-offs between reducing methane emissions and preserving economically valuable traits such as feed intake, carcass weight, and conformation in beef finishing systems.