Male dogs are typically born with two testicles, neither of which have moved from their abdominal cavity into the scrotum. It normally takes about 8 weeks for the testicles to move, descend, into the scrotum. It can take several months for both testicles to fully descend in some dogs. Testicles must move outside the dog's body to produce healthy, motile sperm.
Cryptorchidism and Monorchidism
Cryptorchids are dogs who have abnormally descended testicles. Dogs with cryptorchidism may have either one testicle or both testicles retained in their abdominal cavity. That means the testicles failed to leave the abdominal cavity and pass through the inguinal ring into the scrotum. Cryptorchidism is a genetic condition: Male dogs can pass the condition to male puppies that they sire. Dogs with only one descended testicle are called monorchids. Cryptorchids, particularly monorchids, may be fertile.
Testicular Cancer and Torsion
Testicular cancer and torsion can occur in dogs with untreated retained testicles. Testicular cancer occurs in cryptorchid dogs at a rate of about 10 times that of occurrence in dogs with normally descended testicles. Approximately 50 percent of all retained testicles will develop neoplastic cancer. Dogs with retained testicles should be neutered to prevent the occurrence of testicular cancer.
Torsion occurs when the retained testicle twists on the spermatic cord. This twisting can reduce or cut off the blood supply to the testicle, causing it to atrophy or die. Torsion can cause acute and severe pain when it occurs.
It is often a simple thing to see if a male dog has two testicles. Both scrotal sacs will be filled with a single, firm, oval-shaped testicle. To confirm that the dog has two descended testicles, gently grasp the scrotum between the thumb and forefinger while the dog is standing or lying on his back. Both testicles should be distinct and easy to distinguish from each other.
If the dog has one or both retained testicles, it is possible to locate the testicle(s) by placing him on his back and gently pressing your fingers along the center line of his abdomen. Retained testicles will feel like small, relatively soft balls of tissue beneath the dog's skin. It may be possible to move the retained testicle past the inguinal ring and into the scrotum for easier removal when the dog is neutered.
When palpation does not reveal a retained testicle, the veterinarian may perform an ultrasound examination. This procedure is the most accurate for determining the presence of retained testicles.