CRYPTORCHIDISM; (RETAINED TESTICLES)
A cryptorchid (“hidden testicle”) cat has only one (unilateral cryptorchidism) or no (bilateral cryptorchidism) testicles descended into the scrotum. Males with these conditions should not be allowed to breed because the defect is usually inherited. The parents and siblings of these male cats should also be removed from the breeding pool as they can carry this genetic trait. Since both testes are normally present in the scrotum at birth or shortly thereafter, if they have not descended by six to eight months of age, you should assume that the condition is permanent.
Although retained testicles do not produce sperm, they continue to secrete testosterone and must be removed unless you want your pet to continue to act like a tomcat. As some testicles have a delayed descent, castration is usually delayed until after one year of age. Retained testicles may be more subject to tumor formation, and although this is a rare problem in cats, it is another reason to be sure that retained testicles are removed. To check the testes, see Anatomy.