All unspayed female dogs and cats are at risk for developing pyometra, which is a life-threatening uterine infection that can happen after any normal heat cycle.  During the heat cycle, the cervix opens to allow breeding to occur, and closes after the end of the heat cycle.  If bacteria get trapped inside the uterus during this time, a pyometra (literally meaning "pus-filled uterus") occurs.  This usually happens about 4-6 weeks after a heat cycle.

Symptoms of pyometra include but are not limited to: depression, weakness, lethargy, inappetance, vomiting, fever, foul-smelling or bloody discharge from the vulva, or your pet can just look like she doesn't feel well.  If any of these symptoms occur, especially if you pet has just gone through a heat cycle, call a veterinarian immediately.  Treatment for a pyometra is an emergency spay.  These pets are very sick, so aggressive intravenous fluids, antibiotics, pain medicine, and supportive care are usually necessary.  In some cases, if the pyometra has been present for a while, some of the infected fluid in the uterus can leak into the abdominal cavity or the uterus can even rupture, which is why it is so important to get your pet to the vet immediately if you suspect a pyometra.

If you have a female dog or cat that has not been spayed and you are not considering breeding her, it is important to schedule a spay.  With a spay, the uterus and ovaries are removed so this eliminates the risk for developing a pyometra.  It is much easier on your pet to schedule a healthy spay rather than having to do emergency surgery for a pyometra on a sick dog or cat.  The cost of the spay is also much less when it is a routine surgery.