Incidence of cryptorchidism in dogs and cats

Cats less likely to suffer cryptorchidism than dogs

source: D. Yates el al
Veterinary Record vol 152 no 16, April 19 2003
starts p502, 3 pages long

Testes start to descend after mid-gestation, and, in the case of dogs, they usually travel through the inguinal ring by the time a pup is five days old, being fully descended when a pup is from six to eight-weeks' old. The inguinal ring is usually partially closed by the time a dog is six months' old, preventing migration of any undescended testicles. When testicles to not descend in this way, the result is usually cryptorchidism, with the testicle either hidden in the abdomen, or in the inguinal region. This may affect one or both testicles. There have been different estimates of the incidence of cryptorchidism in cats and dogs. Two studies give estimates for cats of 1.7% and 3.8%, while other studies have given figures for dogs of between 0.8% and 9.7%. Dogs can inherit this condition as a recessive trait, and it has been linked to a higher incidence of testicular cancer. Castration may be carried out both to prevent affected pets from breeding, and to prevent or treat cancer.

This study examines the incidence of cryptochidism in cats and dogs castrated at an English RSPCA hospital from March 1997 to September 2001. Awareness of the owner that their pet might be cryptorchid could affect results, so this was recorded. There were 3,518 dogs castrated in this period, 240, or 6.8%, of which were cryptorchid. Owners believed 129 of them to be cryptorchid, and only 111 were found to be so at surgery. This gives a true incidence of from 3.3% and 6.8% for these dogs. Right-sided inguinal testicles were most commonly found, followed by right-sided abdominal cryptorchidism. There were 3,806 cats castrated, with 50 of them (1.3%) cryptorchid, with owners of 11 cats, or 22%, knowing about the condition in their cats. Inguinal testicles, both left and right side, were most common among the cats, with abdominal and bilateral cyptorchidism being uncommon.

Pedigree dogs accounted for 186 or 77.5% of the dogs, with certain breeds, Chihuahuas, boxers and German shepherds especially likely to be at risk. Other breeds that were overrepresented were Yorkshire and Staffordshire bull terriers, shih tzus, and miniature poodles. Border collies appeared to have a lower than average risk, with 5 of 172 showing this condition, or 2.9%, though the numbers may be too small to be significant. There were not enough dogs for some breeds to make useful estimates. Other studies have mentioned chihauhas, boxers, miniature poodles, and Yorkshire terriers as prone to cryptorchidism. The local population of Staffordshire bull terriers, German Shepherds and shih tzus may have had special characteristics due to inbreeding, or local breed distribution.

Cats showed an incidence of cryptorchidism of between 1% and 1.3%, which was not as high as in other studies where the proportion of pedigree cats was higher. Left testicles were affected in the cases of 29 cats and right testicles in the cases of 27 cats. Owners of only 22% of the affected cats were aware that their cats were cryptorchid, while the percentage for dogs was higher, at 53.8%. The lower level of awareness among cat owners may have been because their cats had not previously visited the clinic.