Why do dairy farmers use the offspring performance of bulls to select sires?

Dairy farmers use the offspring performance of bulls—a process known as progeny testing—because milk production is a sex-limited character. Since bulls do not produce milk themselves, they cannot be evaluated directly for this trait.1

Progeny testing provides the high level of accuracy required to select sires for artificial insemination, which is used to breed approximately 70 percent of dairy cattle. By mating young sires to enough cows to produce 60 to 80 daughters, farmers can evaluate the bulls based on the actual production records of their offspring. This method allows breeders to adjust for environmental factors and isolate the sire's true breeding value. Because these selected sires influence the genetic destiny of the population, this rigorous evaluation process has been highly successful in consistently increasing milk production over time.21