It isn't unusual for a stallion to be 6 years old or older when placed at stud. A major concern for stallion and broodmare owners is the fertility of a new stallion. The high cost of mating, plus mare-mating expenses, makes this an economic consideration. And even if cost isn't a factor, the long gestation period of mares makes this a critical question. If a mare doesn't get pregnant in 2001, she won't have a foal next year.
Several factors can influence a stallion's fertility.
Some stallions just have a low fertility. But the improper use of anabolic steroids can render a stallion infertile. Researchers used semen from the stallions to artificially inseminate 1,055 mares. Fertility in these stallions was evaluated based ln the number of mares that became pregnant in the first cycle and the foaling rate. Stallions varied from 27-82 percent of the mares that became pregnant in first cycle.