Cryptorchidism in Horses

A horse with one or two undescended testes is called a cryptorchid or rig and has a condition called cryptorchidism. A rigs testes are located inside its body near the inguinal canal or abdominal cavity. Some rigs are fertile while others are not but all cryptorchids produce testosterone leading to stallionlike behavior even without testes. Diagnosing cryptorchidism is straightforward and should be done by a veterinarian. Cryptorchidism is usually inherited although it has yet to be successfully genetically mapped.

Breeds like quarter horses saddlebreds Percherons and ponies are more susceptible to cryptorchidism than others 1 Treatment is generally highly effective with a favorable prognosis but a highly specialized veterinary surgeon needs to perform the surgery.
What Is Cryptorchidism?
Cryptorchidism is a condition in horses that causes one or both testes to not descend fully into the scrotum. A cryptorchid horses testes may be located under the skin near the inguinal canal within the canal or outside the abdominal cavity 2 Horses with one descended testis are usually fertile while one with neither testis dropped is usually infertile. Even though the testes dont descend a horse will still have libido and aggressive male behavior because testosterone is being produced 1 Cryptorchid horses may also be referred to as rigs or riglings. Rigs are usually castrated at age three to remove the retained testicle because it can cause discomfort.
Symptoms of Cryptorchidism in Horses
One or two undescended testes are the only reliable sign of cryptorchidism in a horse.
Even if your horse doesnt appear to have testes or is infertile testosterone is in its body. Your rig will display aggressive male behavior regardless of fertility status or outward appearance of testicles. Your horse will likely still be fertile even if only one testicle is descended.

Causes of Cryptorchidism
The cause of cryptorchidism in horses is not entirely understood but there are thought to be several factors at play.
Genetics Cryptorchidism in horses is inheritable but can sometimes occur without a genetic predisposition. While the condition is considered hereditary there has been limited research on the gene that causes cryptorchidism.
Hormonal imbalance Insufficient testosterone may stunt the development of a horses testes causing them not to descend.
Developmental issues Since the testes form prenatally if there are complications with a mares pregnancy cryptorchidism could develop in the horse fetus.
Breed Some breeds appear to be more susceptible to cryptorchidism than others. These breeds include quarter horses saddlebreds Percherons and ponies 1
Diagnosing Cryptorchidism in Horses
To diagnose a horse with cryptorchidism your vet will perform external palpation of