A systematic review and meta-analysis: relationship between residual feed intake and traits related to methane emissions in cattle.

The aim of this systematic review and meta-analysis was to evaluate the relationship between RFI (residual feed intake) and traits related to methane emissions in cattle. Searches were performed in PubMed and Web of Science using keywords in English. The selected studies compared traits related to methane emissions between animals with divergent RFI and/or the correlation between traits related to methane emissions and RFI. Meta-analysis was performed for traits showing three or more uncorrelated results. After application of the exclusion and inclusion criteria, 27 studies were included in the present review. Meta-analysis of the comparison of means was possible for seven traits and meta-analysis of phenotypic correlations for three traits. CH emission (g/day) was significantly lower in negative RFI animals and was positively correlated with RFI, indicating that animals with lower dry matter intake without affecting production traits (low RFI) emit less CH into the environment. However, the results for the other traits evaluated were inconclusive due to insufficient data for meta-analysis. Meta-analyses clearly demonstrated that cattle with lower RFI emit less enteric methane. The primary reason why more efficient animals emit less enteric methane appears to be the reduced availability of substrate for fermentation. Therefore, genetic selection of cattle for feed efficiency, beyond reducing feed costs within the production system, plays a critical role in promoting environmentally sustainable production.