Cryptorchidism in dogs

Cryptorchidism is a fairly common condition where one (unilateral) or both (bilateral) of a dog’s testicles fail to “drop” or descend into the scrotum. This is caused by the inappropriate development of the gubernaculum, a structure which connects the testicle to the scrotum. During typical development, the testicles descend into the scrotum before six months of age, although most puppies have testicles in the scrotum  around two months of age. A veterinarian will palpate the scrotum during a routine puppy wellness check to determine if both testicles have descended yet. 

When one or both testicles do not descend, imaging (an ultrasound or radiographs) may be recommended to locate them. Undescended testicles typically are retained in either the abdomen or the inguinal region (where the abdomen and the back legs meet).

Cryptorchidism appears to be an inherited condition and often seen in families of dogs but the exact cause is not fully understood. It is likely also influenced by both epigenetics (the effect of behavior and the environment on gene expression) and environmental factors. Previous research has found that the prevalence in studied canine populations ranges from <1% to up to almost 10% of dogs. Cryptorchidism is also more common in purebred than mixed-breed dogs.

Signs of cryptorchidism

The main sign of cryptorchidism is a failure of one or both of the testicles to descend. Many puppy owners may not be able to tell if their dog is cryptorchid, and will not find out until their puppy is examined by a veterinarian.

In dogs purchased or adopted as adults, you may see evidence of intact behavior (e.g., urine marking, humping, roaming). In some cases, this may be because your dog has a retained testicle. There is a hormonal test available to determine whether a dog has already been neutered, and your veterinarian may examine the penis for the presence of structures that dissipate after neutering. If the structures are present, your dog may be cryptorchid. 

Complications of cryptorchidism

Breed standard: Because the show ring is an evaluation of breeding quality, dogs who are cryptorchid are not eligible to participate. This condition will put a halt to a dog’s show career. Dogs who are neutered are still eligible for registration with the AKC, and some other AKC events.

Dogs who are cryptorchid also have an increased risk of certain health conditions:

Testicular cancer: When a dog has retained testicles, it greatly increases their risk of testicular cancer (the risk is believed to be 10x greater).

Spermatic cord torsion: This condition is caused when there is a rotation of the spermatic cord (a structure containing nerves and vessels that connects to the testes), blocking blood flow to the testicles. Signs are consistent with inflammation and sudden onset of pain and include nausea and vomiting.

Reduced fertility: Sometimes cryptorchid dogs will have reduced fertility (with bilateral cryptorchidism), although since cryptorchidism seems to have a heritable component, it is not recommended to breed affected dogs. 

Treatment of cryptorchidism

The only available treatment of cryptorchidism is surgical removal of the retained testicle(s).  Even if the condition is unilateral (meaning only one testicle has failed to descend), both testicles should be removed because of the risks of torsion or cancer. Imaging (ultrasound or radiographs) may be recommended to locate the testicle/s, but is not required to proceed with surgery.

The surgery for cryptorchidism may be more complicated than a typical neuter surgery, depending on location of the testicle(s). Most often they are in the abdomen or the inguinal canal, requiring surgical opening of the abdomen, similar to a spay in female dogs.

Prognosis

Surgery for cryptorchidism is considered routine, and most dogs recover completely in 1-2 weeks with some aftercare and reduced activity. Following neutering, if the dog has no other health issues, they can be expected to live a normal lifespan.

Inheritance

The etiology (definitive underlying cause) of cryptorchidism is unknown, but it appears to be inherited. Based on studies of affected dogs and the inheritance patterns based on pedigree, cryptorchidism is thought to be a sex-limited autosomal recessive trait, meaning the gene is present in both male and female animals, but only expressed in one sex (in this case, males). If a male dog receives two copies of the cryptorchidism mutation, they will likely be cryptorchid.  

However, it is likely that cryptorchidism is also polygenic (caused by multiple genes), and that the environment and gene-gene interactions may impact its expression. 

Interestingly, researchers found that when purebred dogs were mated, and both parents were carriers of the cryptorchidism mutation, they had larger litters with more male dogs compared to litters where only one dog carried the mutation. This presents challenges for completely eliminating cryptorchidism in a breeding population. 

Breeding

As there is currently no genetic test for cryptorchidism, breeders must rely on pedigree information to make breeding decisions. However, many researchers are currently working to understand the genetic causes of cryptorchidism, and it is likely that a test is on the horizon.

Affected dogs should not be bred as they will likely pass on the trait to their male offspring and at best, all offspring (male or female) will be carriers. However, it may be unrealistic to eliminate every dog who may be carriers from the gene pool, without increasing the risks of reducing genetic diversity in other ways. 

However, if breeders are producing a large number of cryptorchid puppies (e.g., 12.5 - 25% of male puppies), they are likely breeding a carrier to another carrier, or the mother is homozygous for cryptorchid and the male is a carrier. Breeders should make adjustments to their breeding program accordingly to reduce the production of cryptorchid puppies.

Breeds affected

Smaller breeds, such as toy dogs, may be at higher risk, but any breed of dog can be affected. Breeds believed to be at greater risk include Old English Sheepdogs, Yorkshire Terriers, Bulldogs, Cairn Terriers, Dachshunds, Pomeranians, French poodles, Chihuahuas, German Shepherds, and the brachycephalic breeds.

Resources

VCA: Retained Testicle (Cryptorchidism) in Dogs

Institute of Canine Biology: Cryptorchidism is Complicated

Veterinary Partner: Cryptorchidism (Retained Testicles) in Dogs and Cats

Gubbels, E. J., Scholten, J., Janss, L., & Rothuizen, J. (2009). Relationship of cryptorchidism with sex ratios and litter sizes in 12 dog breeds. Animal Reproduction Science, 113(1-4), 187-195.

https://www.sciencedirect.com/science/article/pii/S0378432008003345

Khan, F. A., Gartley, C. J., & Khanam, A. (2018). Canine cryptorchidism: An update. Reproduction in Domestic Animals, 53(6), 1263-1270.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/rda.13231 

Lea, R. G., Byers, A. S., Sumner, R. N., Rhind, S. M., Zhang, Z., Freeman, S. L., ... & England, G. C. (2016). Environmental chemicals impact dog semen quality in vitro and may be associated with a temporal decline in sperm motility and increased cryptorchidism. Scientific reports, 6(1), 1-14.

https://www.nature.com/articles/srep31281

Willis, M. B. (1963). Abnormalities and defects in pedigree dogs—V. Cryptorchidism. Journal of Small Animal Practice, 4(6), 469-474.

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1748-5827.1963.tb01305.x 

Yates, D., Hayes, G., Heffernan, M., & Beynon, R. (2003). Incidence of cryptorchidism in dogs and cats. Veterinary Record, 152(16), 502-504.

https://bvajournals.onlinelibrary.wiley.com/doi/full/10.1136/vr.152.16.502