Bias of Sire Evaluations for Natural Service Sires and Age of Sire

In the Herdmate Comparison natural service sires often were overevaluated relative to sires in artificial insemination, and younger sires were underevaluated relative to older sires.The Modified Contemporary Comparison was designed to remove these biases.These sire evaluation methods were compared for their evaluation of artificial insemination versus natural service sires.In addition, the Modified Contemporary Comparison and Herdmate Comparison were compared with the Northeast Artificial Insemination Sire Comparison for their evaluation of sires of different ages.Sires from natural service were evaluated lower on the Modified Contemporary Comparison than on the Herdmate Comparison.Younger sires were evaluated higher on the Modified Contemporary Comparison than on the Herdmate Comparison.In both cases the Modified Contemporary Comparison values were intermediate to those of the Herdmate Comparison and Northeast Artificial Insemination Sire Comparison.The Modified Contemporary Comparison appears to remove a substantial portion of the biases favoring natural service and older sires in the Herdmate Comparison.Both the Modified Contemporary Comparison and the Northeast Artificial Insemination Sire Comparison show positive genetic trend.