Differences in production and type trait selection differentials between bulls used in official and owner/sampler dairy herds

Abstract

Differences in the emphasis placed on type and production traits between bulls used in official herds and those used in owner/sampler (O/S) herds registered at the Quebec Dairy Herd Analysis Service were calculated. For 543 881 Holsteins and 41 955 Ayrshires, service records (containing the cow and service sire identification and the service sire's production and type proofs) were used to calculate selection differentials (SD) for the bulls used in official and O/S herds for each 6-mo period between 1980 and 1983. An SD was calculated as the difference between a bull's proofs in a service record and the average proof of all bulls available in the same period. Selection differential means and variances were calculated within each herd, and the average and variance of these means were determined for each 6-mo period. Differences in SD between bulls used in official and O/S herds were determined using the Student's t-test for differences between means. Within Holsteins, SD for final class, general appearance, fore udder, rear udder, size and stature of bulls used in official herds were significantly higher in O/S herds. Within Ayrshires, no significant differences in type-trait SD were found because a very small number of prominent bulls were used extensively throughout both official and O/S Ayrshire herds. Although not significant, in all periods production trait SD tended to be higher for bulls used in O/S herds than for bulls used in official herds for both Holsteins and Ayrshires. Key words: Dairy cattle, bull selection, official, owner/sampler