Pyometra (uterine infection) in Dogs

Pyometra translated literally means “pus in the uterus”.   This is a serious life threatening condition that can occur in any unspeyed bitch but is more common in middle aged to older bitches.  It typically occurs 2-8 weeks after their season has finished.

The bitch is more prone to pyometra compared to other species because they have a fairly unique oestrous cycle (or season/heat).  In most species once they ovulate (release an egg), if there is no pregnancy the hormones levels drop rapidly afterwards.  However in the bitch, the levels of progesterone (a pregnancy hormone) remain high for approximately 9 weeks after they have ovulated regardless of whether they are pregnant or not.  The high levels of progesterone are designed to maintain pregnancy by thickening the uterus lining, removing white cells from the uterus (so the immune system doesn’t attack any developing embryos) and stopping the uterus contracting.  With each successive non-pregnant oestrus cycle the uterine lining gets thicker and thicker and cysts (pockets of fluid) start to develop - known as Cystic Endometrial Hyperplasia.


How do bacteria enter the uterus?

Unfortunately if the bitch is not mated, these high levels of progesterone also predispose the bitch to an infection of the uterus.  During oestrus (heat), the cervix opens to allow the passage of sperm but also can allow bacteria from the vagina or surrounding area to enter the uterus.  With a thickened uterine lining, the fluid from the cysts allows the bacteria to grow and in addition there are minimal white blood cells to fight infection.  Finally, the uterus doesn’t contract to expel bacteria leading to an ideal situation for bacteria to grow and thrive.

If bitches are treated with hormones (progesterone and oestrogen) for various conditions, this can also predispose an unspeyed bitch to pyometra.


Clinical signs

Two types of pyometra are seen – closed and open.  Open pyometra is generally easier to diagnose as the cervix remains open which allows pus to drain from the uterus.  This is generally seen as a sticky discharge which can coat the surrounding hair around the vulva and under the tail.  The bitch will often lick frequently around this area.  Some bitches are otherwise well but some can be very lethargic, off their food and may drink more. 

Closed pyometra occurs when the cervix remains firmly closed and pus collects within the uterus but cannot drain out.  The bitch will very quickly become unwell as the uterus rapidly fills up with pus, and bacterial toxins are absorbed into the blood stream.  These bacterial toxins affect the kidneys so more urine is produced which leads to the dogs drinking more water to compensate.   They rapidly become lethargic and stop eating.  The abdomen may become tense and enlarge to fill with a large volume of pus within the uterus.



If an unspeyed bitch is unwell and examined within 2-8 weeks after their season is finished,  pyometra is always a possible diagnosis.   Open pyometra is much easier to diagnose as pus can be seen draining from the vulva.  Closed pyometra , however, is more of a challenge to diagnose especially early on in the course of the disease.  The bitch may have a high temperature,   may have dilute urine or a firm painful abdomen.  Blood tests often reveal a high white blood cell count and evidence of inflammation.  X-rays can show an enlarged uterus and an ultrasound may be needed to confirm a thickened fluid filled uterus.



The treatment of choice is to perform an ovario-hysterectomy or “spey”.   This involves surgically removing the uterus and the ovaries so the pus filled organ is removed in its entirety, and the ovaries are removed to prevent further production of hormones.   This is a much more risky procedure compared with speying a normal healthy bitch as they are often very unwell.  They will need intravenous fluids, intensive care and antibiotics for a few days/weeks after the procedure. 

If the dog is a valuable breeding bitch then there are alternatives to surgery involving a complicated regime of 2 drugs.  One is an anti-progesterone drug (which prevents progesterone working) and the other is a prostaglandin which again drops progesterone, causes the cervix to open and causes uterine contraction to expel pus from the uterus. Antibiotics are also required.  This treatment is not always successful especially with very sick dogs and there is a risk the uterus may rupture.  If the treatment is successful the bitch must be used to breed on her next cycle as there is a risk that the pyometra may recur.

Left untreated the bitch will eventually die, either from an overwhelming bacterial infection or the uterus can actually rupture releasing pus into the abdominal cavity and a fatal peritonitis.

Early speying, preferably before the second season, is the best method of prevention of pyometra for a bitch not intended for breeding. 

AnimalCare 2002 Limited

Animal Care Vets is actively involved in our local community. We support a number of charities, including the SPCA. We also care for the Hawkes Bay Police dogs. Our customers know by experience that they can rely on us for sound advice on treatment options and that their pet is in the very best hands with our team.