Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/9/2005
Publication Date: 7/24/2005
Citation: Gengler, N., Wiggans, G.R., Thornton, L.L., Wright, J.R., Druet, T. 2005. Accounting for heterogeneous variances in multi-trait evaluation of Jersey type traits [abstract]. Journal of Dairy Science. 88(Suppl. 1):11. Interpretive Summary:
Technical Abstract: 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 mean by fitting a model with fixed effects of mean final score for herd, size of contemporary group, appraisal month, and 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. The 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 Mendelian-sampling SD from HV adjusted evaluations ranged from 22% for udder depth to 48% for teat length of the slope for unadjusted evaluations. This adjustment for HV was implemented in May 2001 and enables more accurate selection decisions.