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Analyses of Sire Comparisons¹

Department of Dairy Science, Michigan State University, East Lansing 48823

ABSTRACT

Sires were evaluated by daughter average and mean weighted difference of first lactation daughters. Herdmates were restricted to first lactation daughters of the other sires in a specific comparison. With large numbers of daughters per sire, the daughter average had similar but generally slightly higher correlations with final predicted difference than did mean weighted differences. Such correlations were .17 and .15 higher for the daughter average in samples of 50 and 100 daughters per sire. These differences are largely attributable to the restrictive definition of herdmates. Using only the few herds having daughters of most or all sires of interest appeared to be an efficient way to select among sampled sires.

Analysis of variance did not show significant interactions for either sire by method of comparison or sire by method of age correction. There was a significant sire by method of record extension interaction, but this had virtually no effect on the sire rankings.

¹ Michigan Agricultural Experiment Station Journal Article 5495.

² Present address: Iowa State University, Ames 50010.