Infertility in a Stallion
History. You are asked to perform a “breeding soundness” examination on a 3-year-old quarter horse stallion that was mated with 10 mares last year and impregnated only one mare. The stallion is in demand because of his bloodlines and because his muscular and mature appearance contributed to winning a number of shows as a yearling.
All the mares mated to this young stallion have been shown to be free of reproductive abnormalities. You ask whether the horse has had any illness or febrile episodes or has received any medication recently. The answer to all these queries is “no.”Clinical Examination. The stallion demonstrates normal libido when exposed to a mare in estrus, and two ejaculates are obtained 1 hour apart by means of an artificial vagina. Examination of both semen samples reveals poor spermato- zoal concentration, low sperm numbers, and a high percentage of morphologically abnormal spermatozoa and immature germ cells. I he stallion has a normal penis and prepuce, but his testes are small and soft. You ask if the stallion has ever received anabolic steroids, and with some reluctance the owner admits that the trainer did give anabolic steroids to the horse in preparation for the yearling futurity and for shows thereafter.
Comment. The use of anabolic steroids in performance animals is not uncommon. Even so, many owners and trainers are reluctant to admit to their use. Many colts are administered these drugs to give them a competitive edge in the show ring or on the racetrack so that they will later be in demand as sires. Unfortunately, because they are testosterone derivatives, the negative-feedback effects of anabolic steroids adversely affect the fertility of these animals, sometimes permanently. It is not known how severe or long-standing the adverse effects will be if anabolic steroids are given in the peripubertal period. Because this animal’s testes are so small and soft, he apparently received high doses of anabolic steroids for a prolonged period during the development of the hypothalamic-pituitary-testicular axis, and the effects are most likely irreversible. It must be noted that as a 3-year-old, the horse is not yet sexually mature, and in the future he may still be able to produce sufficient numbers of normal spermatozoa to impregnate a small number of mares per season, but certainly not a “full book.”
Treatment. Other than time, no known treatment will reverse the detrimental side effects caused by anabolic steroid use in adult males. Even less is known about the long-term effects in young animals. Depending on the percentage of normal, progressively motile sperm, this animal may be able to breed a limited number of mares, most likely through artificial insemination. The owners could also have the stallion reexamined in several months or longer to see if there is any improvement in sperm morphology.