How Well Do You Know Your Stallion?

When a breeding fails, many times the mare is blamed. A large volume of information exists to help breeders understand infertility in the mare, and veterinarians are using the latest technology to assist in the diagnosis and treatment of infertility in the mare.

But what if it's not the mare? What if it's the stallion? How do you know? In order to maximize the reproductive capacity of a stallion--and determine if the problem is originating from him--breeders must understand their stallion's seminal quality.

The best way to do this is to have a veterinarian experienced in stallion reproductive physiology perform a pre-breeding season evaluation. This will establish baseline parameters for your stallion in the areas of sperm motility (movement), total sperm count, and sperm morphology (size and shape). While total sperm count is certainly important, the single most critical seminal parameter is motility. The role of morphology is less understood, and harder to correlate directly with fertility (or subfertility) than the other two parameters.

Schedule the examination at the end of one breeding season and before the next one starts. For most breeders, this occurs in November and December. Timing a fertility work-up in the late fall avoids breeding conflicts and gives you and your veterinarian time to institute some management changes or drug therapy if a problem is discovered. Ideally, you would like to have at least one sperm cycle (60 days) before breeding season begins to see if the treatment worked.

Recognize that the sperm count is going to be low at that time of the year in the northern hemisphere; some breeders and veterinarians like to repeat the evaluation with a "spot check" in March or April, when counts are on the upswing. Know also that there are subtle differences between breeds. For example, Thoroughbred stallions generally have greater total numbers of sperm per ejaculation than Standardbreds. What you're concerned about is whether your stallion fits within the industry's normal limits for his age, breed, level of use, and the time of the year.

If he doesn't, one of the best tools for correcting fertility problems simply is improved management. Manipulating cycles, determining how close a mare is to ovulating, and only covering a mare as often as necessary can maximize a subfertile stallion's reproductive capacity.

Sometimes a stallion needs more than management. If improved timing still isn't getting the job done, it might be time to consider hormonal replacement therapy. The most important physiologic reason contributing to subfertility in the stallion is testicular degeneration. Numerous known and unknown causes exist for this ongoing, progressive disease that can be slowed down or even arrested by administering gonadotropin-releasing hormone (GnRH).

To determine the extent of a stallion's testicular degeneration, and thus his potential for improvement with hormone therapy, your veterinarian will perform a two-part GnRH challenge where blood is drawn before and after administration of the compound. Levels of luteinizing hormone (LH), follicular stimulating hormone (FSH), and testosterone are measured and compared between the two samples, with testosterone serving as the primary indicator of testicular degeneration.

Understanding what normal semen characteristics are for your stallion is important, whether you think he has a fertility problem or not. Stallions which are not producing the quality and quantity of semen that they should might show improvement with management changes, hormone therapy, or a combination of the two.

About the Author

Kirk A. Shiner, DVM

Kirk A. Shiner, DVM, is an member of the American Assocation of Equine Practitioners.

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