Genetic evaluation of conformation traits using random contemporary groupsand reducing the influence of parent averages

A model for the genetic evaluation of dairy bulls and cows for subjectively scored conformation traits using random contemporary groups is proposed. V ariance parameters for the random factors of the model were estimated for 1 4 traits in Jersey cattle. Three alternatives for reducing the influence of parent averages on estimated breeding values were compared using the new m odel. One alternative was to modify the construction of the inverse of the additive genetic relationship matrix, and the other alternatives involved t he application of two artificially high heritability values. Comparisons of estimated breeding values of bulls and cows from the three alternatives an d usual BLUP with the new model were made to determine the effect on rankin gs of animals. Alternatives with higher heritabilities were similar to usua l BLUP, but the modified inverse matrix method caused more rerankings espec ially for cows. The question is whether procedures for calculating estimate d breeding values should be modified to reduce the effect of inbreeding in subsequent selections or whether genetic evaluation procedures should be le ft unaltered and strategies for optimum mating decisions to avoid or minimi ze inbreeding should be adopted. (C) 1001 Elsevier Science B.V. All rights reserved.