When a male puppy is in the womb its testicles are drawn up inside the body. After birth the testicles begin a journey from inside the tummy (abdomen) to the scrotum. Both testicles should have descended to the scrotum by six month of age and be easy to palpate. If testicles do not end up in the scrotum by this age they are said to be ‘retained’. Retained testicles are a relatively common occurrence in male puppies, particularly in certain breeds. If your puppy has retained testicles we will probably recommend an operation to remove them (castration).
If one or both testicles cannot be found in the scrotum by the age of 6 months the dog is considered to be a cryptorchid. Your vet should check for the presence of testicles in the scrotum at the examination at time of first vaccination. If they are not present there by 3 months it is very unlikely they will ever be.
Usually one testicle can be felt in the scrotum but the other has not completed its journey from the abdomen. It may have become stuck anywhere along the way and in many cases your vet will be able to feel the testicle somewhere under the skin. Often the missing testicle is still inside the abdomen and therefore cannot be felt at all.
In most cases cryptorchidism is caused by a defective gene. In order to cause this condition the gene is usually present in both the mother and the father. Since the defective gene may be passed on to future generations animals that are cryptorchid should not be allowed to breed. Breeding should also be avoided from the mother and father of affected animals.
After birth testicles descend into the scrotum because this is colder than the normal body temperature of the animal. If a testicle remains inside the body for many years it is more likely to develop cancer. The cancer of retained testicles is serious and causes significant changes such as hairloss and anaemia (due to excessive hormone production) as well as spreading to other parts of the body.
Another possible serious complication is that of ‘testicular torsion’. If the testicle remains in the abdomen it may become tangled in the ligament that attaches it to the body wall. This can cut off the blood supply to the testicle causing severe abdominal pain. As the testicle is not visible it can be quite difficult to work out what the problem is.
Dogs with both testicles retained are usually sterile (unable to father puppies). Those with one normal testicle can still be fertile, although the quality of their sperm is reduced.
Animals with retained testicles are also more likely to have other genetic defects like umbilical hernias and an abnormal penis.
To avoid future complications dogs with retained testicles should be castrated. 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 – usually by ultrasound but often it is too small to be seen clearly. In any case your vet will need to open up your dog’s belly to remove the missing testicles. This should be done before the dog reaches middle-age to reduce the risk of the retained testicle becoming cancerous.
Since the animal is not suitable for breeding (due to the high risk of passing on the condition) both testicles should be removed – even if one is in the scrotum. This is important to prevent possible future confusion. If the puppy is rehomed and only one testicle is found in the scrotum further surgery might be carried out to try to locate the (already removed) other testicle.