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Effects of Selection Bias on Sire Evaluation Procedures

Animal Physiology and Genetics Institute, Animal Improvement Programs Laboratory, ARS, USDA, Beltsville, MD 20705

ABSTRACT

Problems associated with selected records in methods of sire evaluation have been examined, and multiplicative factors for adjustment have been developed to incorporate later lactation records in sire evaluation procedures where a first record is missing. All Holstein records in the Dairy Herd Improvement Association files at Beltsville, Maryland, with freshening dates between 1960 and 1973 were used to quantify the amount of selection bias in later records that do not have first-lactation information available. Differences for lactation groupings show the amount of bias from selection in these records. The model included an overall mean, effects due to the herd-year-season of freshening, and opportunity groups that were formed depending on the number of later lactations for individual cows. These multiplicative factors can be used to adjust approximately 47% of cows in the files that do not have first-lactation information. These records can be incorporated, if needed to increase accuracy or increase comparisons, in the Best Linear Unbiased Prediction method or the Modified Contemporary Comparison method of sire evaluation.

¹ Sire Program Manager-Holstein, Eastern AI Coop., Box 518, Ithaca, NY 14850.

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