Determining Reproductive Fertility in Herd Bulls

ity of a beef operation is the percentage of the calf crop weaned, which, in turn, is determined mainly by the number of cows bred during the breeding season. The herd bull influences overall herd fertility more than any other single animal. Because the bull also supplies half of the genetics to all of the calves he sires, bull selection can be the most powerful method of genetic improvement in the herd. Accordingly, loss of fertility by a bull can cause substantial loss to a potential calf crop. Since more than 90 percent of the beef cows in the United States are bred by natural service, it is important that bulls be managed to optimize breeding performance. Several factors influence a bull’s fertility. A bull must be developed properly and have reached puberty to be fertile. Other determinants are libido and social dominance as well as physical characteristics, such as scrotal circumference, mating ability, and semen quality play.