Infertility in Female Dogs

What is infertility?

Infertility in a female dog is defined as the inability to conceive and give birth to live puppies, even when mated multiple times with a known fertile male around the time of ovulation.

What is the normal heat cycle in a female dog?

Female dogs normally begin to have estrous (heat) cycles by two years of age. There are several stages in the estrous cycle. Estrus is the stage when the female is in heat, or sexually receptive. Once these cycles begin, the dog should experience estrus at regular intervals. Most female dogs cycle every four to ten months, although some dogs may only cycle once per year.

What causes infertility in female dogs?

Fertility problems in female dogs can be grouped into four broad categories: abnormal heat cycles, failure to mate, failure to conceive, and pregnancy loss.

What causes abnormal heat cycles?

Abnormal heat cycles may be delayed, absent, irregular, or prolonged. 

Primary persistent anestrus is a condition in which a dog reaches two years of age without having a heat cycle. This condition may be caused by several factors, including malnutrition, excessive physical activity, medications that interfere with fertility, or a lack of exposure to other cycling female dogs.

Secondary persistent anestrus is a condition in which a dog has one heat cycle but does not cycle again. This condition is diagnosed when there is a delay of over 18 months since the last heat cycle. In some dogs, this condition is age-related; dogs under two years of age may experience irregular cycles, and the same is typically seen in older dogs.

A variety of infections (e.g., E. coli, brucellosis, ureaplasmosis) and metabolic diseases (e.g., kidney failure, hypothyroidism, Cushing’s disease) may cause illness that prevents normal heat cycles. Exposure to oral and topical steroids (such as those used by humans), hormonal imbalances, and ovarian tumors may also lead to persistent anestrus.

A dog that remains in heat for over six weeks is diagnosed with persistent estrus. Causes of persistent estrus include exposure to hormones from outside the body (intentionally or unintentionally), ovarian cysts that release hormones, and ovarian tumors. Irregular heat cycles indicate that the ovaries are not functioning properly. In this case, abnormal hormone levels are often responsible for a failure to trigger regular heat cycles. Genetic disorders may also prevent normal cycles. 

Some dogs experience a condition called silent heat, in which they ovulate, but the characteristic signs of being in heat, such as vulvar swelling and discharge, are not observed. Although rare, some dogs may also have an autoimmune disease that affects their ovaries and interferes with heat cycles.

What causes failure to mate?

If the time of fertility is inaccurately estimated, the female dog may be unwilling to mate. Many cases of female infertility are likely related to poorly timed breeding.

Behavioral factors may contribute to a refusal to mate. These factors include a dominant female dog refusing to stand for a submissive male , attempts to breed a female that is sexually immature, a stressful or otherwise unpleasant breeding environment, and inappropriate behaviors by either the male or female dog.

Physical factors may contribute to a failure to mate if they cause pain for the female dog. Common physical factors include hereditary abnormalities of the vagina, a history of vaginal trauma, or vaginal growths. Additionally, conditions such as osteoarthritis or back pain may make female dogs unwilling to stand for a male.

What causes failure to conceive?

If breeding is properly timed, the male is known to be fertile, and the semen is handled correctly (in the case of artificial insemination), physical abnormalities of the female may be suspected.

• Infection or inflammation of the uterus may be associated with decreased fertility. Some degree of uterine inflammation, known as cystic endometrial hyperplasia, is observed in many female dogs over six years of age. 
• Infections (e.g., brucellosis and canine herpesvirus) may interfere with conception. 
• Hereditary abnormalities of the reproductive tract may interfere with conception or implantation
• Masses, such as benign uterine polyps or malignant (cancerous) tumors, may interfere with conception.

What causes pregnancy loss?

Pregnancy loss may have several causes. 

• Imbalances in reproductive hormones may result in hormone levels that are too low to sustain a pregnancy. 
• Other hormonal imbalances (e.g., diabetes and hypothyroidism) may affect reproductive hormone levels and result in pregnancy loss. 
• Certain medications (e.g., corticosteroids) may lead to fetal death.
• Some infections can lead to fetal death. (e.g., brucellosis).

How will my veterinarian determine the cause of my dog’s infertility?

Your veterinarian will begin with a complete physical exam and a review of your dog’s medical and breeding history. The findings may suggest a cause and help guide further testing. Tests may include:

• Blood and urine tests. A complete blood cell count, blood chemistry tests, and a urinalysis help assess your pet’s overall health and identify other medical conditions.
• Infectious disease testing. Your veterinarian will likely test for the presence of brucellosis and may test for other infectious diseases depending on the physical exam and blood and urine test results.
• Hormone tests. These may measure progesterone (a hormone that helps maintain pregnancy), estradiol (a hormone involved in heat cycles), and relaxin (a hormone involved in embryonic loss).
• Vaginal cytology and culture. Your veterinarian will take a swab from your dog’s vagina for examination under a microscope and bacterial culture. The types of cells present help identify the stage of your dog’s heat cycle. A sample of vaginal material may also be submitted for bacterial culture, to assess for infection.
• Imaging. X-rays or ultrasound may reveal abnormalities in the abdomen.

How is infertility treated?

The treatment of infertility depends on the cause. Ovarian cysts or tumors require surgical removal, hormonal imbalances may need to be corrected, and infections require treatment. Medications can be used to bring dogs into heat if they are not cycling. The success of this technique varies, but it can lead to successful breeding.

Improving the timing of breeding is often helpful. The most effective approach is to measure hormone levels to determine the day of ovulation. For natural breeding, the dogs should be allowed to mate every other day for as long as the female will allow it. With artificial insemination, the best timing depends on the type of semen used and the method of insemination.

Regardless of fertility status, all breeding female dogs should be provided with a clean, low-stress environment and a high-quality, well-balanced diet. Avoid raw diets in breeding dogs due to the risk of infections that may contribute to infertility. Work with your veterinarian to determine the best course of action for your dog.