The importance of this step becomes obvious in many cases by checking the sires of calves in the calf pens. Only a few bulls are needed to breed all the cows. Fortunately, we have an industry in place in the United States to identify and distribute semen on the very best sires in each dairy breed. Use of those superior sires will determine genetic change in dairy herds. Dairy farmers work with cows, not bulls, and sometimes feel intimidated that sires are so important to genetic change.
Females generate dollars on dairy farms, so their importance is assured.
However, the biology of reproductive rate dictates that breeding values can be estimated most accurately on the males and that only the very best bulls need be used. Turning to sire selection for genetic gain is only a practical, logical business decision. Sire selection controls the flow of desirable genes into a dairy herd. The purpose of genetic improvement is to increase the frequency of good genes in a herd, not merely to combine mediocre genes in the least damaging way. Optimally, both benefits can be achieved by combining good sire selection with corrective matings.