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Why You Should Spay Your Cat: Pyometra

Updated: Dec 3, 2021

My first pyometra surgery was a few years back. A fairly young cat, maybe 5 years of age. The prognosis for a young female with a pyometra is good when you catch them early and get them spayed.

Well, earlier this month, we had a case of pyometra in a three-year-old female intact, fully indoor cat. The owner woke up that morning, and there was blood on her floor. There was a bit of a panic, and she booked an appointment with me. I took a history, found out that she wasn't spayed, my technician triaged her. Her temperature was 38.6 degrees Celsius, which is in normal range for a cat. The only thing abnormal on her physical exam was that she had bloody discharge coming from her vulva.

I threw the ultrasound on her belly, and this is the image I took. We have a really ancient ultrasound machine, which we usually just use for cystocentesis (ultrasound guided urine collection). But I was able to identify the uterus.

As you can see from the image, the uterine wall thickness is about 1 cm, the lines on the y-axis are 10 mm apart. I didn't do the surgery, my colleague did, because I was off on the Monday. When we saw each other again, he said it was a "good one" i.e. it was pretty darn thick!

Since often my cases come in threes, so it seems, I'm going to continue this in another post... to be continued here. But let's discuss why your veterinarian recommends to spay.

Why You Should Spay your Female Non-Breeding Dog or Cat

Ok, I get that your indoor only cat is not going to get pregnant. You've been dealing with her yowling while she is in heat, trying to make a call to any male cat in the vicinity to breed with her. A minimal problem that you have managed to deal with, including every time she goes into heat she is peeing outside of her litter box.

With each heat cycle, the ovaries are signaling to the uterus to prepare for pregnancy. This increases the thickness of the uterine lining. Without a pregnancy, there are cysts left behind. With the changes in the uterus, comes abnormalities of the cervix, and bacteria from the outside world are more likely to creep through the cervix into the uterus. Dogs and cats do not shed their uterine lining like female humans do (contrary to popular belief, dogs do not have a "period"). Inflammatory conditions can lead to cancer - which is another story - in this case, bacteria taking up residence inside the uterus can lead to sepsis. Sepsis is bacteria in the blood stream and sepsis can lead to death. The only way to prevent a pyometra is to spay your cat or dog. If they are a retired breeding female, you should also get them spayed.

The other thing that we know is that spaying your female dog and cat reduces their risk of mammary carcinoma (breast cancer). Mammary carcinoma is really a death sentence in a cat. In the majority of cases, by the time they go for surgical removal of the lump in their mammary tissue it has already spread. In cases that go for surgery and chemotherapy, you may get an additional 6 months of life. Unless you are catching the lump really early, and removing it before its spread, then maybe you can get an additional year of life after surgery.

In dogs, if you spay prior to their first heat the incidence of mammary carcinoma is close to zero (I think the stats were 0.8% likelihood when I was going through school). If you spay after their first heat, but before their second, the chance of development mammary carcinoma is 7% (that's a big jump from zero to 7% likelihood). If they go through a second heat cycle, then it's 1 in 4 dogs that are intact will develop mammary carcinoma. Earlier this year I euthanized an intact female dog that was only 7 years old, who had mammary carcinoma that was causing fluid in her lungs due to metastasis. I can tell you that a dog drowning in its own fluids due to cancer (or heart failure) is a really, really bad way to die!

So, there are medical reasons to spay your cat and dog, not just for unwanted pregnancy.


For veterinary students, click here for more information on surgery for pyometra. I do not recommend to sew over. Just flush the stump. Otherwise you are going to trap bacteria in the crevices.


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