Cryptorchidism occurs when one or both testicles do not descend into the scrotum; both are usually present, but one or both are retained in the body cavity. The concern is that the retained testicle leads to cancer in the older dog and should be checked by a veterinarian. While not generally considered a serious health risk, if both testicles have not descended by 6 months of age, you must consult with your veterinarian as soon as possible. Retained testicles do not produce spermatozoa but do produce testosterone and are more likely to become neoplastic than are descended testicles. The animal is fertile if cryptorchidism is unilateral.
Pedigree dogs, in particular the German Shepherd Dog, Boxer, and Chihuahua are most commonly affected. Among the dogs, right-sided cryptorchidism is the most common form, followed by right-sided abdominal cryptorchidism. The location of the affected testicle(s) is most variable in the Boxer. There are no behavioral changes associated with cryptorchidism in dogs.
A single autosomal recessive gene has been cited as a probable cause. The wide breed distribution of cryptorchidism in the dog suggests that inheritance may not be the only factor. Many experiments have been performed to identify the factor responsible for the descent of the testis in dogs. There are indications that the Sertoli cells (germ cells) and testosterone have an important action on the descent. Bilateral castration is recommended in all cases.
A report on a population of breeding dogs exhibit a 26 year (1988–2014) decline in sperm quality and a concurrent increased incidence of cryptorchidism in male offspring (1995–2014). A decline in the number of males born relative to the number of females was also observed. Environmental chemicals, including diethylhexyl phthalate (DEHP) and polychlorinated bisphenol 153 (PCB153), were detected in adult dog testes and commercial dog foods at concentrations reported to disrupt reproductive function in other species. Testicular concentrations of DEHP and PCB153 perturbed sperm viability, motility and DNA integrity. The direct effects of chemicals on sperm may therefore contribute to the decline in canine semen quality that parallels that reported in the human.1
- Environmental chemicals impact dog semen quality in vitro and may be associated with a temporal decline in sperm motility and increased cryptorchidism. Richard G. Lea, Andrew S. Byers, Rebecca N. Sumner, Stewart M. Rhind, Zulin Zhang, Sarah L. Freeman, Rachel Moxon, Holly M. Richardson, Martin Green, Jim Craigon, and Gary C. W. England. 2016