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Bias and Mean Square Error from Ignoring Genetic Groups in Mixed Model Sire Evaluation

Department of Animal Science, University of California, Davis 95616

ABSTRACT

Criteria based on mean square error were developed to determine whether differences among genetic groups ought to be included in sire evaluation. Simulation was used for a population of 2000 first lactations from daughters of 50 sires with 25 sires per group. Designs were simulated for semen exchanges between groups of 5,10, 25, and 50% both one-directional and reciprocal. Analyses were with and without the inverse of a matrix of numerator relationships among sires. The matrix averaged 10.3 and 5.8% related sire pairs within and between groups, respectively. For unrelated sires, mean square error of sire evaluation ignoring genetic groups was less than including genetic groups when true genetic differences between groups were less than 176.7, 132.4, 103.1, or 93.9 kg for one-way exchanges of 5, 10, 25, or 50% and 126.0, 102.8, 84.6, or 79.3 kg for reciprocal exchanges. For related sires, corresponding genetic differences were 179.8, 137.1, 109.5, or 100.5 for one-way exchanges and 131.1, 109.1, 92.1, or 87.2 for reciprocal exchanges. For only two groups, ignoring genetic groups leads to smaller mean square error of sire evaluation if the true genetic difference is less than the standard error of estimate of the difference between groups.

¹ Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada N16 2W1.