Bias in Sire Evaluation Due to Selection

Abstract

The first and second lactation records of New York artifically sired Holstein cows were analyzed to determine the effect of culling after the first lactation on sire evaluation based on both first and second lactation records. Results indicated that weighting first and second 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 first and second records. Even with a pronounced differential culling rate after the first lactation, there was no evidence of a differential bias in valuating sires of different genetic merit based on first and second lactation records.