Normal testicular descent should be evaluated at the first veterinary examination. Retained testicles are a relatively common occurrence in male puppies, particularly in certain breeds. Cryptorchidism is the term for failure of one or both testicles to descend into the scrotum. This process should be completed by 6 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 inside of 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 both in the abdomen. If only one testicle is retained, this is known as unilateral cryptorchidism. If both testicles are retained, this is known as bilateral cryptorchidism. If your puppy has retained testicles your veterinarian will probably recommend a special operation to remove them (cryptorchid castration).

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An undescended testicle is not able to produce sperm and tends to be smaller than the scrotal testicle because of the warmer temperature inside the body. However, it still produces male hormones in particular, testosterone. If both testicles are cryptorchid, the dog will usually be sterile (infertile). Dogs with one cryptorchid testicle are usually still fertile from the scrotal testicle, although they may have less sperm than a normal male. No known, ethical medical or surgical treatment can cause the affected testicle to descend. Some young male dogs eventually have descent as late as 7 months of age, but this is still not normal and is also a genetic problem. Cryptorchid testicles are more prone to problems such as torsion and cancer, especially if in the abdomen. Neutering (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 intra-abdominal surgery and 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 at all is to neuter the animal as a juvenile or young adult dog. The current guidelines for timing neutering, especially in large breed dogs, to promote orthopedic health can still be followed as long as the dog is not bred or allowed to age beyond 18-24 months.

Both parents are implicated in the inheritance, so the mating should not be repeated. The trait is sex limited (seen only in males) but not sex linked (carried by both sexes). Since this trait is inherited, it is important not to breed this male as he can pass it on to his offspring. Related female puppies could be carriers when their brothers are either carriers or cryptorchid themselves.

Dogs with retained testicles should be castrated (both testicles removed) at the earliest opportunity and should not be used for breeding. There is no ethical or proven effective way to medically or surgically induce testicular descent. Removing retained testicles can be a difficult operation as they may be located anywhere in the abdominal cavity. Sometimes the internal testicle can be detected beforehand using ultrasonography, and this makes the operation easier for the vet to plan. However, often the missing testicle is too small to find ultrasonographically and so your vet will have to make a large incision (cut) into your dog’s tummy to open them up and look for the retained testicle. Some vets may use laparoscopic (keyhole) surgery to locate and remove the testicle, but even then, may need to convert to a full surgical procedure if the testicle cannot be located or removed laparoscopically. There is always a small risk that your vet will not be able to locate the missing testicle and further tests, or follow-up surgery may rarely be required. Since the animal is not suitable for breeding (due to the high risk of passing on the condition) both testicles should always be removed – even if one is in the scrotum. This is also important to prevent possible future confusion. If the puppy is ever lost, stolen or rehomed and only one testicle is found in the scrotum then future vets may not know that a cryptorchid testicle has already been removed and may put the dog through unnecessary further surgery trying to locate the testicle. Likewise, if only the normal scrotal testicle is removed, then future owners and vets will presume the dog is castrated and be unaware that a retained testicle remains and could be developing serious health issues. Ethically, it is always appropriate to remove both testicles – even if one is healthy.