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Cryptorchidism is the term for failure of one or both testicles to descend into the scrotum, a process that should be complete by 8 weeks of age. During development, the testicles are located just behind the kidneys. Each testicle is attached to a cord, called the gubernaculum, whose other end is attached to the scrotum. As the cord shrinks, it pulls the testicle down through the abdomen, through an opening in the body wall called the inguinal ring, under the skin, and into the scrotal sac. Therefore, the undescended testicle is found in the abdomen, in the inguinal ring, or under the skin between the rear legs. If both are undescended, which is less common, they are usually in the abdomen.

The undescended testicle is not able to produce sperm and tends to be smaller than the scrotal testicle because of the higher temperature inside the body. If both testicles are cryptorchid, the dog is sterile. Dogs with one cryptorchid testicle are usually still fertile from the scrotal testicle, although they will have less sperm than a normal male. There are no known medical treatments can cause the affected testicle to descend. Since this trait is inherited, it is important not to breed affected males as they can pass the condition on to their offspring. Related female puppies could be carriers when their brothers are either carriers or cryptorchid themselves.

Cryptorchid testicles are more prone to problems such as torsion and cancer. Neutering, which is surgically removing the testicles, can prevent these problems from occurring. An abdominal testicle can twist upon itself, which is referred to as testicular torsion. This torsion cuts off the blood supply to the testicle and causes severe pain to the animal. The only treatment is emergency neutering.

Testicular cancer is the second most common tumor in older dogs. Cryptorchid males are up to 13 times more likely to develop testicular cancer than normal dogs. Neutering is the best treatment if cancer develops, sometimes followed by chemotherapy. The only way to prevent this type of cancer from occurring is to neuter the animal as a young dog.

*This article may not be reproduced without the written consent of the UC Davis School of Veterinary Medicine.

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