Bias in Sire Evaluation Due to Selection

Abstract
The 1st and 2nd lactation records of New York artificially sired Holstein cows were analyzed to determine the effect of culling after the 1st lactation on sire evaluation based on both 1st and 2nd lactation records. Results indicated that weighting 1st and 2nd records according to number of records per cow, repeatability, and heritability evaluated sires almost identically with the method which uses the average of a daughter''s 1st and 2nd records. Even with a pronounced differential culling rate after the 1st lactation, there was no evidence of a differential bias in evaluating sires of different genetic merit based on 1st and 2nd lactation records.

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