Stud breeders are collectively responsible for effecting genetic change in the commercial (producer) herds. To do this stud breeders record animal performance and sell (primarily) male progeny to commercial herds to generate the next crop of offspring.
The standard model has two levels of stud herds: elite and multiplier herds (Figure 1).
Elite herds are the top tier. They supply progeny to the multiplier herds and commercial herds. The genetic progress of elite herds is determined largely by their stag selection decisions. Multiplier herds are the next tier. They purchase progeny from elite breeders and sell to commercial herds. The genetic progress of multiplier herds is dictated largely by the stags they purchase from the elite herds.
This is, of course, a simplified model and many real situations may not completely fit this. Whatever stud breeder a commercial selects, the primary consideration should be matching the stud herd their breeding objective with the commercial herd production goals ensure they have a good positive genetic trend for the traits, indexes or BV's that fit those goals. Stud breeders need to be continually improving so the whole industry can improve.