Cryptorchidism in Horses

What is Cryptorchidism in Horses?

Cryptorchidism is the condition where a horse’s testicles do not descend into their normal position in the scrotum. If both testicles are undescended, the horse is considered a bilateral cryptorchid. A unilateral cryptorchid means only one testicle is undescended and the other is in its normal position.

Breeds that are most commonly affected by this condition include: Percherons, American Saddlebreds, American Quarter horses, ponies, and crossbred horses. Thoroughbreds have the lowest prevalence.

Immediate health effects of cryptorchidism are minimal. They are essentially healthy horses. The cryptorchid testicle does not cause pain, unless in the very rare circumstance that it twists on its cord. Then it will swell and become painful. Long term, the undescended testicle may be more at risk of developing testicular cancer.

Special management considerations would be deciding where to house a cryptorchid horse (i.e., not with mares that you do not want bred) and consulting with your veterinarian on when and where to have them gelded.

Symptoms of Cryptorchidism in Horses

The most obvious clinical sign a horse is experiencing cryptorchidism is that one or both testicles are not visibly present.

Cryptorchid horses will still exhibit sexual behavior because the cells of the undescended testes are functional and produce testosterone, although at reduced amounts.

Causes of Cryptorchidism in Horses

Cryptorchidism is caused by the failure of both hormonal and mechanical events that normally occur in the foal’s development to take place. The testes are formed inside the developing foal’s abdomen. They move into the scrotum sometime between the end of pregnancy and the first few weeks after birth. Special ligaments and pressure building in the abdomen cause this to occur. This process is also under hormonal control, but the exact details are still not completely understood.

In a cryptorchid horse, the undescended testicle or testicles may remain anywhere along the path they travel during development—from inside the abdomen and into the scrotum. Most stallions will have their testicles completely descended by 4 weeks of age. However, it can be normal for this process to take 18 to 24 months. If after 24 months both testicles are not easily palpated in the scrotum, the horse is considered a cryptorchid.

How Veterinarians Diagnose Cryptorchidism in Horses

Manual palpation (feeling) of the scrotal and the horse’s history are the first steps in working towards a diagnosis of cryptorchidism. The only way to know for sure that a horse is not a cryptorchid is to feel two descended testicles or to have history of a bilateral castration having been performed.

In some instances, especially in a young horse, a veterinarian may think they feel a small testicle in the scrotum, but it is actually the epididymis (a narrow, tightly-coiled tube that is attached to each of the testicles), thus missing a diagnosis of cryptorchidism.

A diagnosis can be difficult to attain without a known history for the horse and will require diagnostics tests and imaging. Careful palpation with the horse under sedation will help a veterinarian in finding the undescended testes. The addition of transabdominal and transrectal ultrasonography during this exam may be beneficial.

One or more tests can be performed on bloodwork and help to with the diagnosis:

• Testosterone level

• Serum estrone sulfate level (only useful in horse over 3 years old)

• Anti-Mullerian hormone (AMH)

If a diagnosis cannot be made based on the above tests, the next step is surgery. During surgery, the veterinarian will look for either the retained testicle or the cut end of the testicular cord in order to determine if the horse was previously castrated.

Treatment of Cryptorchidism in Horses

Surgical removal of a cryptorchid testicle (called a cryptorchidectomy) is the treatment for cryptorchidism in horses. This is performed under general anesthesia in either a field or hospital setting. 

It is critical for the surgeon to completely identify all parts of the testicle and epididymis before finishing the surgery in order to prevent a partial castration. 

In more complicated situations, like bilateral abdominally retained testicles or a horse with an unknown history, a laparoscopic procedure is recommended. This must occur in a hospital setting due to the special laparoscopic equipment that is required.

At the time of the procedure the horse should receive a tetanus vaccine and non-steroidal anti-inflammatory medications. If entrance into the abdomen is needed or occurs during the procedure, antibiotics should also be administered.

Recovery and Management of Cryptorchidism in Horses

Exercise and “return to work” recommendations are based on the surgical procedure. In most cases, activity should be restricted to stall rest for 24 hours followed by gradual return to exercise over the next 10-14 days.

As with any surgical procedure and more specifically castrations, complications may occur. These can include excessive bleeding, evisceration (bowels protruding out through incision), infection, abscess, and swelling.