Evaluating the Breeding Stallion: What Does the Practitioner Need to Know?

The objective of a breeding soundness examination is to determine whether a stallion has the mental and physical capabilities to deliver semen, containing viable spermatozoa and no infectious disease, to the mare's reproductive tract at the proper time. The examination not only evaluates quality and quantity of ejaculated spermatozoa but also tests the libido and mating ability of a stallion, attempts to recognize congenital defects that may be transmissible to offspring and/or decrease a stallion's fertility, seeks infectious diseases that may be transmitted venereally, and searches for problems that may reduce breeding longevity. As such, a physical examination of the stallion is an integral part of a breeding soundness examination.

An appreciation of normal genital anatomy is essential to competent physical examination of the stallion's reproductive tract.
of two testes and attached epididymides, contained within a scrotum; paired deferent ducts, which traverse the spermatic cord to enter the caudal abdomen, then penetrate the genital fold to terminate in the pelvic urethra; four distinct accessory genital glands; a musculocavernous penis; and its protective prepuce.

Measurement of total testicular volume offers important information to the examiner. The value provides information on the predicted number of spermatozoa that a stallion should be capable of ejaculating on a daily basis. If the actual daily sperm output is less than predicted daily sperm output, then reduced spermatogenic efficiency can be expected. The formula for determining testicular volume is as follows:

Testiclar volume (cc) = 4/3 • (W/2 x H/2 x L/2) = 0.5236 WHL,

where W = testicular width (in cm) H = testicular height (in cm) L = testicular length (in cm)⁴ [...]