Genetic Merit and Usage Patterns of Bulls from Different Sampling Programs

¹ Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061-0315

Modified Contemporary Comparison and January 1991 animal model evaluations were used to categorize bulls. Bulls born from 1970 through 1981 were classified as AI- or non-AI-sampled and further divided as used (returned to service) or unused after first-crop evaluation. Bulls used heavily prior to proving were grouped separately. Groupings were effective because number of herds and daughters in first-crop and most recent animal model evaluation differed significantly across the five categories of bulls. Category of use, year of birth, and interaction were significant for PD milk from first-crop evaluation and PTA milk from January 1991 animal model. Least squares means from first crop evaluation were –161, –128, and 35 kg for unused AI, heavily sampled AI, and unused non-AI bulls and 129 and 213 kg for AI and non-AI bulls returned to service. Least squares means for January 1991 animal model evaluations were –262, –196, and –75 kg for unused AI, heavily sampled AI, and unused non-AI bulls and 87 and 84 kg for AI and non-AI bulls returned to service. Although non-AI-sampled bulls declined considerably relative to AI-sampled bulls, their average final genetic merit for milk was similar to that of AI-sampled bulls born in the same year. Risk of change in evaluations of non-AI-sampled bulls should be considered when determining extent of use.

Key Words: genetic merit • progeny • sampling • Modified Contemporary Comparison

Submitted on June 17, 1991
Accepted on August 5, 1991

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