During development before birth, the testicles migrate from the abdomen into the scrotum. Normally this is complete by 10 days of age. Cryptorchidism means that one or both of a dog's testicles have not descended into the scrotum. If this does not happen by 8 weeks, the dog is generally diagnosed as cryptorchid, although the testicles may still descend up to 4 months or so.
This is a fairly common condition, which is seen most often in the toy and miniature. Although the condition is of course seen only in male dogs, both males and females can carry the gene for cryptorchidism. Heterozygous males and females, and homozygous females, will be physically normal, but can pass the gene on to their offspring. Homozygous males are cryptorchid. Thus cryptorchidism is thought to be a sex-limited autosomal recessive trait.
Dogs that are cryptorchid have a much increased risk of testicular cancer (approximately 10 times). Castration will of course eliminate this risk.
Affected dogs should be not be bred. It is best not to breed their parents as well, who carry the gene.
