Each testicle starts out inside the abdominal cavity of the kitten and descends into the scrotum after passing through the inguinal canal in the groin. Normally, testicles are present in the scrotum at birth or shortly afterward, although they may be very small and difficult to detect. By the age of 6 to 8 weeks, they should be large enough to be palpated. However, the testicles may not stay in the scrotum permanently until 4 to 6 months of age. Until that time, the cremaster muscles can retract immature testicles into the groin.
Cryptorchidism refers to the failure of one or both testicles to descend into the scrotum and remain there by 7 to 8 months of age. While unilateral cryptorchidism is most common, it can be bilateral. The mode of inheritance is suggested to be recessive and polygenic, and cryptorchid males should not be used for breeding. Unilateral cryptorchid males may be fertile and so should be castrated.
Is It An Inherited Trait ?
Cryptorchidism is an example of a sex-limited trait. The trait is physically expressed only in the male even though it can be carried by females. Both the sire and dam of an affected cat should be considered to be carriers. Some full siblings of an affected cat will also be carriers. A reduction in the number of cryptorchid cats in a breeding program can be achieved by removing affected males and carrier parents from breeding. If the problem is widespread in a family line, full siblings of an affected cat should also be eliminated from the breeding program.
How Common Is It?
In dogs, the incidence of cryptorchidism has been estimated at 1.2%. In contrast, a study done at the Animal Medical Centre, New York found that the rate of cryptorchidism in cats seen at that institution was 3.8%. The most commonly represented purebred cat in this survey was the Persian (20% of cases). Other represented breeds included the Himalayan (6%) and Siamese (4%). DSH cats represented 50% and DLH cats represented 6%. Most cryptorchids were unilateral (90%) and of these cats, the left and right sides were equally affected. In cats where the location of the retained testicle was recorded in the medical record, 49% were in the groin, 33% were in the abdomen, and 14% were within the inguinal ring. Two cats in this study (2%), a Burmese and an Abyssinian, were monorchid (only one testicle was present). Spermatic cords and vessels were present but ended blindly with no testicle.
Another study done at Michigan State University looked at the incidence of cryptorchidism in cats over a 10-year period (1980-1989). This study found an incidence of 1.7%. Two cats were monorchid (0.1%). Persians were also over represented in this study with an incidence of 29%. Most cryptorchids were unilateral (78%) in this study as well. The bilateral cryptorchids all had retained testicles present in the abdomen. Tissues from abdominally retained testicles were examined and no sperm were found. It is likely that abdominally retained testicles are sterile because the higher temperature inside the body will suppress development of sperm. Cats with retained testicles located outside the abdomen, however, may be fertile.
Fig. 2 The penis of a neutered male cat has no spines. They disappear within 6 weeks of castration.
Is There a Recommended Treatment ?
There is no treatment proven to cause a retained testicle to descend into the scrotum. Treatment with hormones called gonadotropins has not been successful. In other species, surgical removal of the retained testicle and castration are routinely recommended because the retained testicle is at risk for cancer or torsion and evidence for a heritable cause is more definitive. Torsion of the spermatic cord has not been documented in the cat and testicular tumours are very rare in this species. However, the probability that cryptorchidism is inherited in the cat is sufficient reason to recommend castration and removal of the retained testicle in purebred cats. Cryptorchid cats that have only the scrotal testicle removed will display all the normal behaviours of an intact male. Therefore, it is important that both testicles be removed when the cat is destined for a pet home.
Fig. 3 Surgery to remove two retained testicles. Both testicles were found in the cat’s abdomen, near the kidneys which is where they develop during fetal life.
1. © Dr Susan Little; http://www.catvet.homestead.com/Cryptorchid1.html