heterogeneous variance adjustment; type evaluation
Résumé :
[en] The multi-trait genetic evaluation system for type traits was modified to estimate adjustments for heterogeneous variance (HV) simultaneously with estimated breeding values (EBV) for final score and 14 linear traits. Heterogeneity, estimated for transformed traits, was regressed within parity toward the population variance means by fitting a model with fixed effects of mean final score forherd, size of contemporary group, appraisal month, and appraisal year-season and a random effect for interaction between herd and appraisal date. Method R was used to estimate variances for the heterogeneity model in each EBV iteration. Data was from the 766,725 appraisals included in the official November 2004 evaluation. Parent averages were calculated from evaluations with recent appraisals removed. Annual trends for cow EBV were lower with HV adjustment than for unadjusted EBV for all traits. The SD of Mendelian sampling (evaluation minus mean of parent evaluations) declined less over time for HV adjusted than for unadjusted evaluations. The slope at year 2000 of Mendeliansampling SD from HV adjusted evaluations was only 22% for udder depth to 48% for teat length of the slope of that for unadjusted evaluations. This adjustment for HV was implemented in May 2001 and should make selection decisions more accurate by using these proposed integrated HV adjustments.
