Re-ranking in International Beef Cattle Evaluations due to ignoring Direct-Maternal Genetic Correlations Between Countries

Abstract

Many traits of economical relevance in beef cattle are influenced in their phenotypic expression by the dam. Genetic evaluations of maternally affected traits require to model direct, maternal and direct-maternal genetic (co)variances next to non-genetic effects. In Interbeef beef cattle international evaluations, direct-maternal genetic correlations (r_dm) may be different both within countries (r_{dm_WC}) and between countries (r_{dm_BC}). r_{dm_WC} for growth traits up to weaning are often reported to be negative and significantly different from zero. As r_{dm_BC} are difficult to estimate, these are currently assumed to be equal to zero in Interbeef evaluations. The objective of this study was to evaluate the impact of using estimated values for r_{dm_BC} instead of assuming them to be zero, on international estimated breeding values (IEBV). We implemented two scenarios that differed only in the modelling of r_{dm_BC}: A) the current Interbeef evaluation with assumes r_{dm_BC} to be 0 and fits estimated r_{dm_WC}, and B) an Interbeef evaluation in which both estimated r_{dm_WC} and r_{dm_BC} were fitted. Weaning weight phenotypes and pedigree information were available for more than 3 million Limousin beef cattle males and females, born between 1972 and 2017, and distributed across ten European countries. We evaluated the impact of ignoring r_{dm_BC} on different groups of animals by comparing animals’ direct and maternal IEBV between scenarios A and B. Ignoring r_{dm_BC} resulted in no re-ranking for direct IEBV, and limited re-ranking for maternal IEBV. Less re-ranking in maternal IEBV was observed with increasing reliability. Moreover, ignoring r_{dm_BC} resulted in no re-ranking for publishable sires, i.e. of sires with IEBV that can be exchanged across countries. Our study suggests that the current practice of ignoring r_{dm_BC} has limited impact on Interbeef evaluations when r_{dm_BC} are close to 0 on average (ranging from +0.14 to -0.14) as is the case for weaning weight.