Retained testicles, or cryptorchidism, may involve one or both testicles. It is due to errors in development. The testicle forms near the spine and migrates from there down into the scrotum. It is attached to a ligament that lengthens as it migrates and once the testicle is in place the opening into the scrotum from the abdomen narrows, holding it in place. Sometimes the testicle goes off-course, sometimes the ligament isn’t long enough or contracts (almost 5% of young puppies with descended testicles later permanently retracted them – 2009-10 ASHGI health survey), or the opening closes too soon (or the testicle arrives too late) preventing it from descending. While the medical terminology for the condition is “cryptorchid,” dog jargon uses that word to mean both testicles undescended and “monorchid” for one.
Generally speaking, if the testicles have not descended by 4 months of age they probably won’t. However, they will sometimes come down later, even several months later though this is extremely unusual. If the dog is of good quality, give him some time to see what happens. Retained testicles are not desirable, mostly because testicles retained within the body cavity are sterile. The sterility is caused by the body heat – the reason they normally reside in a pouch outside the body. There is also an increased risk of testicular cancer; however, this cancer is rare in dogs so the overall risk to health may be minor. Locating and removing the retained testicle requires abdominal surgery, the extent of which can vary with the location of the retained testicle. Surgery also carries risk. Discuss the issue with your vet.
This is a disqualifying fault, so an affected dog could not compete in conformation. The 2009-10 ASHGI health survey found 4% of males are affected, a disturbingly high frequency for something that is not only a disqualifying fault but which renders some males completely sterile. Retained testicles are sex limited in that, for obvious reasons, only a male can have them. However the genes that control formation and descent of the testes into the scrotum are not on the Y (male) chromosome, so either sex can have and pass the genes. Because of the variety of errors in physical structure of the testicles and related or adjacent tissues that can cause a testicle to be retained, inheritance is probably complex. Do not breed affected males. Parents and full and half siblings of an affected dog should not be bred close on the pedigree that produced it nor to mates with a family history of retained testicles.