When a racing or performance stallion is retired to stud, many owners choose to purchase first-season subfertility insurance, also called congenital infertility insurance, against the possibility that he might be infertile. Veterinary examination of the prospective breeding stallion is required and, generally based solely on the size of his testes, the veterinarian is asked to judge whether the stallion might have acceptable fertility and how many covers he should handle per day.

At the 2008 American Association of Equine Practitioners convention, held Dec. 6-10 in San Diego, Calif., a discussion of the calculations a veterinarian can use to estimate a stallion’s fertility and capabilities was presented by Terry Blanchard, DVM, MS, Dipl. ACT, professor of veterinary medicine at Texas A&M University. All of the calculations are based on testis size as measured by calipers or ultrasound (Blanchard’s preferred method).

A practitioner might collect the following measurements from a stallion:

•  Total scrotal width (across both testes);
•  Left and right testicle widths, heights, and lengths;

These measurements can be compared with published reference values