Effects of Genetic Merit of Herdmates on Sire Summaries for Type in Holstein Cattle

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Abstract
Official classification records (755,744) of the Holstein Association of America were used to ascertain effects of genetic merit of herdmates on sire evaluations for type. Progeny were stratified into 3 groups on herdmate average for final score: low (< 79.75), middle (79.75-81.75) and high (> 81.75). Predicted differences (PD) for type were computed in each group for 670 sires with 20 or more progeny in each of the herdmate groups. Mean PD''s for type for 3 herdmate groups were 0.12, -0.28 and -0.45, indicating that failure to adjust for nonrandom use of sires affected herdmate comparisons for type. The correlation between herdmate average and average PD for type of herdmates'' sires was 0.48 and between herdmate average and average Cow Index Type of herdmates was 0.45. Two iterative procedures and a mixed model comparison were examined as alternatives to sire evaluation by herdmate comparison. All were effective in reducing differences by herdmate groups. Proofs in the low group still were favored slightly by all 3 models. The mixed model comparison appeared to be the most effective in reducing effects of nonrandom usage.