De-regressing MACE versus domestic EBV for genomics
Keywords:de-regression, genomic evaluation
De-regressed EBV are commonly used phenotypes in national genomic evaluation systems. This study compared REML estimates of variance for de-regressed MACE proofs of foreign sires on the Canadian scale, versus de-regressed national EBV of domestic sires. Variances for nearly all traits were higher for foreign than domestic sires. Ratios of SD for foreign relative to domestic sires, based on December 2010 Holstein data were; 1.05 and 1.07 for protein and fat yields, 1.17, 1.04 and 1.24 for mammary system, feet & legs and conformation, 1.50 for cow survival and 1.20 for cow non-return rate. Based on current data from December 2014, some of the more extreme ratios of SD were closer but still higher than 1. After applying a variance adjustment to de-regressed MACE proofs of foreign sires, genomic validation results improved for all traits. Slopes of regression, of the 2014 Canadian LPI index of trait EBV, on the 2010 genomic-enhanced parent averages (GPA), increased from 0.93 to 0.97, and biases of over-prediction for top young genomic bulls were accordingly reduced.
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