CONSIDERATION OF SIRE RELATIONSHIPS FOR ESTIMATION OF VARIANCE-COMPONENTS WITH INTERACTION OF HERD AND SIRE

Effects of sire relationships for sire and interaction of herd and sir e were examined using simulation and minimum variance quadratic unbias ed estimates of variance components. Data were simulated for 50 herds and 20 sires for five sire relationship matrices, three data structure s, and three interaction levels. A total of 1000 replicates were simul ated for each combination of relationship matrix, data structure, and interaction level. The minimum variance quadratic unbiased estimates w ere calculated for the true (simulation) model, for models ignoring re lationships for sires and interaction, and for models excluding intera ction of herd and sire. Interaction variance was underestimated when r elationships were ignored. Underestimation increased with sire related ness. Sire variance and heritability estimates increased when variance components were estimated using sire models compared with estimates u sing interaction models. This overestimation increased with interactio n level simulated in the data and as the data were more unbalanced. Es timates of sire variance were as much as 2.7 times larger than that ex pected, and heritability estimates were as much as 2.8 times larger th an that expected.