Genetic Differences Among Categories of Service Sires

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Abstract
Service status was determined for Holstein sires in service from 1971 through 1984. Categories were defined by sire''s sampling status (AI vs. non-AI) and whether sire was proven at time of use (young vs. proven). A sire''s category could change over time. Genetic merit was the latest PD milk through January 1988. For each service year, minimum sire usage limits were set so that service sires were representative of the category; e.g., young sires in AI sampling were required to have at least 20 daughters in USDA predigree files from services in a given year. Although 80% or more of sires were non-AI, 80% or more of services were AI. Use of AI increased across years, and a higher percentage of active AI sires were from AI sampling. The AI sires were 211 kg superior to non-AI sires for PD milk and 292 kg higher on a weighted basis (i.e., considering differential usage). Differential usage raised average of active AI sires by about 90 kg compared with simple mean across sires. Sires in AI sampling were of essentially equal merit to active AI sires, which suggests that they would average at percentile 50, but active AI sires were higher by an average of 108 kg if differential usage was considered.