Sire Evaluations with Parities as Correlated Traits and Comparison with Single-Trait Evaluations

All lactation records are included in sire evaluations for milk components by mixed model methodology by the United States Department of Agriculture.To increase accuracy of these evaluations, procedures were investigated for processing information from different parities as correlated traits rather than as a repeated single trait.The current model for matureequivalent records, which includes fixed group, random sire, fixed herd-yearseason, and random cow effects, was modified to include a separate sire effect for each of first three parities.Residual variances for different parities were assumed uncorrelated and of equal variance and, therefore, could be factored out of mixed model equations.Cows and herdyear-seasons were absorbed prior to iteration.Sire equations then were augmented by addition of direct product of the inverse of the relationship matrix and the inverse of the matrix of genetic variance among parities.Sire solutions were obtained by block iteration, with blocks consisting of group equations and three equations for each sire.Evaluations were computed for 591 Ayrshire sires with 13,551 daughter records for milk and fat yields and 447 Guernsey sires with