Sexual differentiation begins with fertilization. Like humans, female dogs inherit two X chromosomes, while male dogs inherit an X and a Y chromosome. After chromosomal differentiation, hormone differences in utero control the development of the organs associated with each sex, including the uterus, vagina, vulva, and clitoris in females, and the penis, testes, and scrotum in males. A problem at any point along the way can result in a Developmental Sexual Disorder (DSD). Disorders that occur in chromosomal differentiation will give the dog an abnormal number of chromosomes. Dogs with extra chromosomes may appear normal, or they may have ambiguous genitalia. If the problem occurs during development, dogs will have normal chromosomes but may have the opposite sex organs than that which is typically associated with their chromosomes, called complete or partial sexual reversal. Dogs with sexual reversal are usually infertile, and they may also have ambiguous or hermaphroditic sexual organs. Hyperplastic genitalia are typical with all types of DSD, including an enlarged clitoris, an abnormal penis, and complete or partially retained testes. Some dogs have chronic irritation of the genitals. Others exhibit no abnormal symptoms until their owners try to breed them. DSD can occur as a direct mutation (often the case with abnormal chromosome differentiation), an inherited condition in some breeds, or environmental factors during development such as pregnant dams being exposed to sex steroid hormones. DSD is relatively rare in dogs.

Disorders of sexual development can cause infertility and abnormalities in the genital organs of dogs. This can be either inherited or due to environmental factors during pregnancy. DSD usually becomes apparent during a dog’s first breeding season.

These are some of the symptoms you might notice in dogs with DSD.

There are several different types of DSD.

Sex Chromosome DSD (abnormality in chromosome differentiation) 

XX DSD (pseudohermaphrodites or true hermaphrodite) 

Retained testes (cryptorchidism) 

There are three main causes for DSD in dogs.

Some abnormalities may be detected on a physical examination if the clitoris or vulva is enlarged or if there is an abnormal penis. Skin irritation or dermatitis, which is common with hypoplastic organs, will also be obvious. The veterinarian may take cultures to evaluate for concurrent infection and other possible causes (pyometra, a severe uterine infection, is more likely with an abnormally developed uterus).

X-rays or ultrasound will check for internal abnormalities, such as retained testes, as well as the presence of cancerous tumors. Exploratory surgery may determine the extent to which your dog has ovarian or testicular tissue. Many dogs with DSD have a combination of both. Blood and urine tests will typically be normal unless other diseases or infections are present. The veterinarian may also test your dog’s sex steroid hormones, which are generally below normal with DSD. Karyotyping will be used to identify disorders with abnormal chromosomes.

Your dog’s breeding history can be important. Most DSD becomes evident around a year old when dogs are first bred unless the sexual organs are very noticeably abnormal. In older dogs, abnormal sex organs and infertility might be due to a different cause, such as exposure to sex hormone medication, or testicular or ovarian cancer. Breed and family history can also be relevant since DSD often runs in families.

Spaying or neutering is the recommended treatment for DSD in dogs. An ovariohysterectomy or a gonadectomy will remove any abnormal tissue or retained testes. The veterinarian will usually remove enlarged clitorises or abnormal penises at the same time, especially if there is pain or irritation in this area. Penal reconstructive surgery could be needed for male dogs with the urethra in an abnormal place as a result of DSD. 

Depending on your dog’s exact anatomy, surgery is likely to be similar to a typical spaying operation. Your dog will probably spend a day in a veterinary hospital after the operation. Pain medication may be prescribed and you will need to keep any incisions clean and dry. A period of reduced activity will last about two weeks. You may need to return for a check-up or to remove stitches. If your dog is not healthy enough for surgery, creams and pain medication may be prescribed to manage any genital irritation.

Most dogs with DSD are infertile but otherwise they still make good pets and can live relatively normal lives. Spaying or neutering is recommended since DSD usually comes with an increased risk of infection and/or cancerous neoplasia. Occasionally dogs with DSD from abnormal chromosomes can be fertile. If this is the cases, and your dog isn’t experiencing any genital irritation or other problems, treatment may not be needed. This will depend on the advice of a veterinarian.