Factors Affecting Selection of Mates of Sires in Arteficial Service

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Abstract
Matings of 10,922 registered Holstein cows from 1964 through 1967, to 142 sires, were identified through two artificial in- semination organizations. Each sire had a minimum of 10 mates. Mates' mature equivalent records were used to compute bias in sires' Predicted Differences due to nonrandom selection of mates. The mean bias was 13.2 and .6 kg for milk and fat with standard deviations of 14.7 and .6 kg. Rank correlations between Predicted Differences, uncorrected and corrected for the bias, were .996 and .992 for milk and fat for the 126 bulls with published proofs. Price by itself accounted for approxi- mately one-half of the variation in bias. Multiple regression of bias on a subjective popularity score and type and production proof data indicated that price and sire's type score were the most important fac- tors in predicting bias.