Estimators of Sire Merit

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Abstract
Nearly 7,000 first lactations of daugh- ters of 90 sires in 187 progeny test herds were used to compare estimators of sire merit. The standard model among the several contains fixed effects of herd- year-seasons and sire groups and random effects of error and sires within groups. The estimate of merit for a sire is the sum of the appropriate group and sire within group estimates from a general- ized least squares solution. This approach accounts for sires of herdmates, considers the number of daughters and herdmates in each herd-year-season, and simultane- onsly regresses sire constants toward ap- propriate group means. Three definitions of groups, as well as a model not includ- ing groups, were compared with the conclusion that virtually any grouping is preferable to ignoring groups for sires in general. Two herdmate comparisons, Predicted Difference, and regressed-mean weighted difference were compared, and evaluations by the latter approach were more like those from standard method. Both herdmate comparisons ignore the merit of sires of herdmates. Neither this omission nor ignoring environmental cor- relation seriously altered evaluations of the majority of sires.

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