Breeding Soundness Examination of the Stallion
Dr. Sylvia Bedford-Guaus
Based on all the results obtained during the breeding soundness examination (BSE) a stallion may be classified as a Satisfactory, Questionable or Unsatisfactory Prospective Breeder. Immaturity. Stallions bred too soon (the optimal age depends on the particular stallion) may have suboptimal libido, poor semen quality, reduced sperm numbers or low fertility rates. For stallions < 3 years of age, in which one of the above problems is identified, it is usually advised to recheck the stallion the following season, before making any definitive judgment about their potential fertility.
To be considered a Satisfactory Prospective Breeder, a stallion must pass all the tests performed during the BSE, and must be producing a minimum of 1 billion progressively motile, morphological normal sperm in the last ejaculate collected during the BSE.
A Questionable Prospective Breeder is a stallion that presently displays some problem that precludes his classification as Satisfactory. However, this stallion may pass a BSE performed at a later date. An example would be a young stallion that is expected to improve with age or a stallion that was recently sick and his semen quality has been affected, but is expected to improve over time.
An Unsatisfactory Prospective Breeder has a problem that is not expected to improve. Examples of this would be stallions with genetic abnormalities or very old stallions with advanced testicular degeneration.
If you are planning to purchase a breeding stallion, you should always request that a BSE be performed, and then only buy the stallion if classified as Satisfactory. You may consider purchasing a stallion that is classified as Questionable only if you fully understand why the stallion did not pass the evaluation at this time, and optimally with a purchase agreement contingent to the stallion passing the exam at a future evaluation.
Testicular degeneration. All old stallions (>15 years old) may have some degree of testicular degeneration, which is manifested by low sperm numbers and poor sperm quality in the ejaculate. This type of testicular degeneration is often irreversible. However, some young stallions may also have some degree of testicular degeneration if they have been exposed to some insult such as toxic chemicals, radiation or high temperatures such as an episode of fever. This may be reversible if the insult or cause of trauma is removed.
Reproductive tract infections. These are diagnosed by the presence of white blood cells (pus) in the ejaculate paired with a positive culture from a swab obtained from the reproductive tract or semen. Infections are most commonly located in the urethra (urethritis) and the accessory sex glands (seminal vesicles). Treatment is difficult and requires long-term administration of antibiotics.
Hemospermia. This term basically means bleeding into the semen or bleeding during ejaculation. The most common causes of this problem are infections and lesions (wounds, tumors) in the urethra. Blood is spermicidal and this compromises fertility. The primary problem should be treated and in the meantime, semen used for breeding should be diluted with an extender to thin out the toxic effects of red blood cells towards sperm.
Blockage of the reproductive tract. In some stallions the ductus deferens (tube that connects the testicle with the urethra) may become blocked with dead sperm or epithelial cells preventing normal ejaculation. These stallions seem to perform normally and may appear to ejaculate during breeding or semen collection, but no sperm or only dead and tailless sperm are seen in the ejaculate. With repeated semen collections, internal massage and medications these stallions may be successfully unblocked, pass a breeding soundness examination and have a successful breeding season. The problem may recur, usually but not always, at the beginning of the next breeding season and this should be closely monitored.