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Consideration of Sire Relationships for Estimation of Variance Components with Interaction of Herd and Sire

Department of Animal Science, 239 Kildee Hall, Iowa State University, Ames 50011

Effects of sire relationships for sire and interaction of herd and sire were examined using simulation and minimum variance quadratic unbiased estimates of variance components. Data were simulated for 50 herds and 20 sires for five sire relationship matrices, three data structures, and three interaction levels. A total of 1000 replicates were simulated for each combination of relationship matrix, data structure, and interaction level. The minimum variance quadratic unbiased estimates were calculated for the true (simulation) model, for models ignoring relationships for sires and interaction, and for models excluding interaction of herd and sire. Interaction variance was underestimated when relationships were ignored. Underestimation increased with sire relatedness. Sire variance and heritability estimates increased when variance components were estimated using sire models compared with estimates using interaction models. This overestimation increased with interaction level simulated in the data and as the data were more unbalanced. Estimates of sire variance were as much as 2.7 times larger than that expected, and heritability estimates were as much as 2.8 times larger than that expected.