Case reports of cryptorchidism in cats have appeared occasionally in the veterinary literature, but there is little detailed incidence data available on cryptorchidism in large populations of cats presented for castration. As well, scant data are available on the incidence of cryptorchidism in various pedigreed breeds.

Records of 4,140 cats presented for castration to two feline-only veterinary hospitals over a 10-1/2 year period (January 1993 to June 2003) were examined. Seventy-two cats (1.7%) were identified as cryptorchid. This incidence is similar to the findings in other studies (range 1.3% to 1.9%) of large numbers of cats, but lower than that reported in one smaller study (3.8%). Incidence rates reported in dogs in recent studies vary from 2.6% to 6.8%.

Three cats (< 0.08%) in the current study were identified as monorchid (two Persian/Himalayans, one random bred). This finding is lower than the incidence of monorchidism identified in an earlier study (0.15%) that involved a smaller number of cats.

Of the 4,140 cats presented for castration, 437 (10.5%) were pedigreed cats, representing 22 breeds. The incidence of cryptorchidism in pedigreed cats was 6.2%, significantly higher than that for non-pedigreed cats (1.3%). The incidence of cryptorchidism in pedigreed dogs is also higher than that for random bred dogs. Eight cat breeds were represented by 10 or more individuals (Table 1).

Table 1. Incidence of cryptorchidism in eight pedigreed breeds

The highest incidence of cryptorchidism was found in the Ragdoll breed (18.75%), although only a small number of Ragdoll cats (16) were included. Previous studies have found the incidence of cryptorchidism in the Persian breed to be as high as 29%. In the current study, which included a larger number of Persian/Himalayan cats than previous reports, the incidence in the breed was 10.4%.

The location of the retained testicle(s) was known for 62 of the 72 cryptorchid cats. Most cats (88.7%) were unilateral cryptorchids. The most common configuration was the unilateral, inguinal cryptorchid (51.6%). Right unilateral and left unilateral cryptorchids were similarly represented. Previous reports have shown conflicting data on the most common location of the unilaterally retained testicle. In the unilateral cryptorchids of this report, the retained testicle was significantly more likely to be inguinal. Only 7 of the 61 cats (11.3%) were bilateral cryptorchids; 2 (3.2%) cats were bilateral inguinal and 5 (8.1%) cats were bilateral abdominal cryptorchids.

In conclusion, this represents the largest and most comprehensive study of cryptorchidism in cats and includes new data on pedigreed breeds. Cryptorchidism in general is less common in cats than in dogs. Pedigreed breeds of cats are more likely to be cryptorchid than random bred cats and the highest rate of cryptorchidism was found in the Ragdoll breed.