Maternal body composition in seedstock herds. 5. Individual-trait selection direction aligns with breeder perspectives on maternal productivity

The present paper quantifies the variation in selection direction and genetic merit for the 10 Angus seedstock herds that contributed the majority of the data to the industry herd component of the Beef CRC Maternal Productivity Project. Differences in multi-trait selection direction for 17 BREEDPLAN estimated breeding values (EBVs) ranged between 16 and 63 degrees. Important differences among herds for selection direction for individual EBVs were identified. Specifically, some herds had been selecting to increase rib-fat and rump-fat EBV, while others were decreasing them. On the basis of a principal component analysis, 78% of the between herd difference in genetic merit as assessed by 17 EBVs was accounted for by two principal components. For 2000-born calves, the first principal component accounted for 50% of the genetic variation between herds and was most closely associated with days to calving EBV. Of the genetic merit for 2009-born calves, the first principal component accounted for 49% of the between herd variation and had the strongest weightings with BREEDPLAN rib-fat and rump-fat EBVs. The second principal component accounted for 29% of the variation and was most strongly related with BREEDPLAN EBVs for traits gestation length, milk and eye muscle area and 200-, 400- and 600-day weight. The variation at 2009 is consistent with outcomes from qualitative research that hypothesised that the main differences in genetic merit among herds are associated with rib-fat and rump-fat EBVs, but there were also differences in selection emphasis for weight traits. Despite differences in genetic merit among herds being generally small, they will manifest themselves in different productivity outcomes depending on the management system. Seedstock breeders and bull buyers should be aware of this and target their animal selection accordingly.