Re-ranking in International Beef Cattle Evaluations due to ignoring Direct-Maternal Genetic Correlations Between Countries
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 (rdm) may be different both within countries (rdm_WC) and between countries (rdm_BC). rdm_WC for growth traits up to weaning are often reported to be negative and significantly different from zero. As rdm_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 rdm_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 rdm_BC: A) the current Interbeef evaluation with assumes rdm_BC to be 0 and fits estimated rdm_WC, and B) an Interbeef evaluation in which both estimated rdm_WC and rdm_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 rdm_BC on different groups of animals by comparing animals’ direct and maternal IEBV between scenarios A and B. Ignoring rdm_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 rdm_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 rdm_BC has limited impact on Interbeef evaluations when rdm_BC are close to 0 on average (ranging from +0.14 to -0.14) as is the case for weaning weight.
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