Counting To Two by D. Caroline Coile, Ph.D. Human parents may rejoice at counting 10 fingers and 10 toes, but dog breeders need only count to two to be grateful: two testicles, that is. At birth a male puppy’s testicles are still within the abdomen, but they slowly descend into the scrotum by about 10 days after birth. They may be hard to locate at first, but by 6 to 10 weeks they should be easily located in the scrotum. If not, there is only a small chance they will descend. However, they are soft and can still move between the scrotum and inguinal canal, especially when the pup is cold or scared, so they may appear to come and go until the pup’s inguinal rings close at about 6 months of age. At that time, a dog with only one descended testicle is termed a unilateral cryptorchid, and one with no descended testicles is a bilateral cryptorchid. The reported incidence of cryptorchidism in dogs ranges from 1 to 10%, with many more almost certainly unreported. Unilateral cryptorchids occur more often than bilateral, and the retained testicle is usually the one on the dog’s right side. Cryptorchidism is reported most often in Toy Poodles, Pomeranians, Yorkshire Terriers, Miniature Dachshunds, Cairn Terriers, Chihuahuas, Maltese, Boxers, Pekingese, English Bulldogs, and small or short-nosed breeds in general. In humans, about 3-6% of newborn males are cryptorchid, rising to 9-30% in premature males. Low birth weight, being one of a twin, and maternal exposure to estrogen during the first trimester all predispose a human male to cryptorchidism. Hereditary factors are assumed to play an important role even in humans, where 7% of brothers of cryptorchids are also cryptorchids. Certain inbred families of dogs, notably Cocker Spaniels and Miniature Schnauzers, have increased rates of cryptorchidism. Some of the most telling data come from selective breeding in goats. Deliberate use of cryptorchid sires raised the incidence in a goat herd from 7% to 51%; then subsequently in that same herd strict selection against cryptorchids (using only entire sires, and using neither a parent of a cryptorchid nor offspring of a known carrier) decreased the incidence to 1%. The genetics aren’t known, although it’s commonly speculated that the trait is a sex-limited (that is, can only be seen in males) autosomal (non-sex chromosome) recessive (takes two) trait, meaning that both males and females can be carriers. That means that if a breeder seriously wants to rid the trait from a line, then not only affected males, but sisters, mothers, and dams of affected males must be pulled from the breeding pool. This would create such a devastating blow to most gene pools that it’s not reasonable. Another possibility is that cryptorchidism is a polygenic trait, that is, arises from the interplay of multiple genes. This would make it even more difficult to control. Cryptorchid dogs can’t be shown in conformation, and bilaterally cryptorchid dogs are sterile. A retained testicle is about 10 times more likely to become cancerous, and its spermatic cord is also more likely to become twisted causing testicular torsion, but the chances of both are still fairly low. Nonetheless, because of these potential problems a retained testicle should usually be surgically removed. Breeders hoping to avoid these problems often turn to veterinarians for help in encouraging a reluctant testicle. In humans, surgical correction is the treatment of choice. The same procedure is possible in dogs, but because such treatment is considered a fraudulent change of appearance by the AKC, and because such dogs could then be used at stud and perpetuate the trait, veterinarians consider it unethical. Drug therapies are often tried. Much controversy exists over whether such treatment is effective because few if any studies include control cases. Repeated doses of drugs such as human chorionic gonadotropin (HCG) or gonadatropin releasing hormone (GnRH) are given to stimulate androgen production, which in turn appears to influence testicular descent by affecting the testicular cord or cremaster muscle. In humans, no difference in efficacy has been found between 4 doses compared to 10 doses of HCG; nonetheless, it is commonly given twice a week for five weeks. Success rates in humans range from 6-21 % in randomized blind studies, and much higher in uncontrolled studies. GnRH may give better results, and is available as a nasal spray instead of injection, but is only improved for treatment of cryptorchidism in humans in Europe. Success rates in controlled human studies range from 6-38%, and in uncontrolled studies from 13-78%. In a comparison of HCG and GnRH, the HCG had a success rate of 6% and the GnRH 19%. Some investigators advocate using both therapies. These percentages only apply for humans. Little hard data is available for dogs, but one study in which HCG was given four times over a two-week period reported success in 21 out of 25 dogs, with better results when given to puppies less than 16 weeks old. Some veterinarians and breeders consider even drug therapy unethical. However, side effects are minimal, and if medical treatment can reduce the need for abdominal surgery in a hunt for retained testicles, it would seem unethical not to try it. Retained testicles predispose dogs to some medical problems, but in many breeds the most serious threat it poses is euthanasia. The sad truth is that dogs in breeds in which pet homes are seldom available may be euthanized because they cannot be used for show. And while breeding such dogs may raise the probability of producing more cryptorchids, the condition is not as devastating as many other conditions dogs are routinely bred with. Until the time a DNA test becomes more available, and the mode of inheritance and other possible factors are better understood, breeders will continue to make their best bet and then hold their breath and count to two.