I. Reproductive Anatomy and Hormones

The reproductive tract in a female dog consists of the ovaries, uterus, cervix, vagina, and vulva. The ovaries are located in the abdomen just behind the kidneys. The uterus is made up of two long bodies called horns. The horns of the uterus are where puppies are carried during pregnancy. The horns meet at the body of the uterus. The body of the uterus ends at the cervix, which can be open or closed. The vagina extends from the cervix to the vulva, which is the external opening of the reproductive tract.

Reproductive Anatomy of the Female Dog

The reproductive cycle, or estrous cycle, of the female dog is divided into four phases:

• Proestrus


• Estrus


• Diestrus


• Anestrus

The length of time from the beginning of one cycle to the beginning of another cycle can vary from four to twelve months. Movement from one phase of estrus to another phase is controlled by hormones.

The phases of proestrus and estrus together are what is known as “heat” in a female dog. The average length of time that each phase lasts is nine days but they can last anywhere from two to twenty-one days. During proestrus, a dog’s vulva swells, her teats may also swell, and she may have bloody discharge coming from her vulva. Estrus is what is known as “standing heat,” when a female dog will allow a male dog to breed with her.

During proestrus and estrus, the level of the hormone estrogen is high. Estrogen prepares the uterus to become pregnant by causing it to swell and causing glands in the lining of the uterus to swell. Estrogen also causes red blood cells to seep into the uterus. These red blood cells are what cause the vulvar discharge to appear bloody. Estrogen levels begin to fall during estrus and levels of the hormone progesterone begin to rise.

Diestrus lasts from two to three months (60-90 days) depending on whether or not a dog is pregnant. Progesterone levels are high and estrogen levels are low during diestrus. Progesterone helps the uterus maintain a pregnancy, if there is one, during the diestrus period.

During anestrus, neither estrogen nor progesterone levels are high.

II.What is Pyometra?

Pyometra can be simply defined as an infection in the uterus. Infections almost always happen during diestrus, usually about two months after the last time the dog was in “heat,” but can also happen immediately after a dog has had puppies. During this time, the level of progesterone is high. Progesterone decreases the motility of the uterus and makes it more susceptible to infections. Once bacteria get in the uterus, they easily grow.

Pyometra is classified based on whether the cervix is open (an open pyometra) or closed (a closed pyometra). The older a dog gets, the more likely she is to develop a pyometra.

III.What to Watch for at Home – Symptoms

Symptoms will depend partly on whether the cervix is open or closed. They usually begin about two months after the dog was last in heat. Dogs that develop a closed pyometra are usually much sicker than dogs with an open pyometra. This is because with an open pyometra, bacteria and pus can drain from the body. Symptoms can include:

• Lethargy or lack of energy


• Depression


• Lack of appetite (anorexia)


• Drinking excessive amounts of water (polydipsia)


• Urinating excessively (polyuria)


• Vulvar discharge that is cloudy or looks like pus (with open pyometra)


• Vomiting


• Weakness


• Running a fever (usually with a closed pyometra)

Discharge from the vulva does not have to be present. Dogs with a closed pyometra may have very little discharge.

IV.The Veterinary Visit – How to Tell if a Dog has Pyometra

The diagnosis of pyometra is usually suspected based on the history of the dog (recently in heat) and the physical examination. Usually an enlarged uterus can be felt when the abdomen is palpated. If an open pyometra present and there is discharge from the vulva that looks like pus, this together with the history and examination will be all that is needed to make a diagnosis. Usually, blood work will be run also. This usually shows an elevated white blood cell count.

In some cases, the diagnosis is not as straightforward. If there is no vulvar discharge or very little vulvar dischage, as occurs with a closed pyometra, the diagnosis can be harder to reach. Some other tests which will need to be run in this case include:

• Abdominal x-rays – X-rays will show an enlarged uterus. Together with the physical examination findings and history of the dog, this will likely enable the veterinarian to make a diagnosis.


• Abdominal ultrasound – If ultrasound is available, it is preferred over x-rays. Ultrasound allows the veterinarian to see inside the uterus and differentiate between the things that might cause the same symptoms.


• Blood progesterone level – The progesterone level should be high in a dog that has a pyometra, but not in dogs that have other diseases that might cause similar symptoms.

X-Ray of a Dog with a Closed Pyometra - The two round, whiter, tubular structures at the bottom are the horns of the uterus

V.Treatment and Prevention

The best treatment for a pyometra is surgery. Usually a dog with pyometra will be hospitalized for a few days surrounding the surgical procedure. An IV will be placed. The IV will be used to give fluids and antibiotics before and after surgery. During surgery, the ovaries and infected uterus are removed. This is an ovariohysterectomy, or spay. The majority of dogs, except for those that are severely ill, recover quickly once the uterus is removed. How long a patient stays in the hospital after surgery depends on how quickly they recover. When a dog is eating and drinking on it’s own and can take oral antibiotics, it is ready to go home.

For dogs that are used for breeding, there is a medical treatment for pyometra. This involves giving injections of prostaglandins (other hormones). Prostaglandins stimulate the uterus to contract, relax the cervix and help to lower the blood progesterone level. Antibiotics should be given at the same time as the prostaglandins. Treatment with prostaglandins can be dangerous. In some cases, the uterus can rupture requiring emergency surgery.

Medical treatment is usually not recommended because it is more dangerous and because a dog that has developed a pyometra once is at a high risk of developing another. If medical treatment is used, a dog should be bred during the next heat cycle after treatment.

Pyometras can be prevented by spaying female dogs before their first heat cycle. There is no health or behavioral benefit to having a dog go through a heat cycle or have a litter of puppies. In fact, having even one heat cycle signficantly increases a dog’s risk of developing mammary (breast) cancer later in life.