Genetically more efficient Australian dairy cows and sheep are higher emitters of methane per unit of food

Abstract: Both the dairy cattle and sheep industries face the simultaneous challenge of improving feed efficiency and reducing methane emissions. Genomic selection is a valuable tool to reduce residual feed intake (RFI) and reduce methane yield (MeY), which are widely used traits for estimating efficiency and emissions. However, it is important to know how selecting one of these traits would affect the other and this relationship has been contentious in the literature. Here we estimated the genetic correlations between RFI and MeY in 584 Holstein dairy cattle and 445 Australian Maternal Composite ewes using bi-variate genomic best linear unbiased prediction models. In both datasets, negative genetic correlations between RFI and MeY were found, which means that selecting more feed efficient animals would increase the amount of methane emitted per kg of dry matter intake. Diet could play a role in this relationship.