This disease can take your pet from perfectly healthy to dead in just 4 days.

When we see puppies for vaccinations one question that’s always discussed is whether to have the pet spayed (female) or neutered (male). This blog post explains why non-breeding females should always be spayed.

Unfortunately, most people think that the only reason for spaying is to prevent unwanted litters. While that’s a laudable goal, there are several other reasons to have your female puppy spayed. In my opinion the most important of those is a medical condition called pyometra (or pyo for short). (The latin root “pyo” refers to sepsis or pus, while the root “metra” typically refers to anything involving the uterus.)

Closed pyometra
This large structure is a closed pyometra. The uterus (large heart-shaped tube) is full of pus.

Pyometra is a condition in dogs in which the uterus gets severely infected and often fills with pus. Pyometras occur because dogs experience a much different hormone cycle than women and most other mammals. To understand why dogs get pyos so easily you need to understand the role of progesterone in the pregnancy cycle. After a bitch ovulates, the ovaries then produce a structure (called the corpus luteum, or CL) that produces progesterone. Progesterone prepares the wall of the uterus for implantation of the fertilized eggs, or embryos. For simplicity sake, I always explain to clients that while estrogen is the “get pregnant” hormone, progesterone is the “stay pregnant” hormone.

In women who ovulate and then don’t get pregnant, progesterone is only elevated in the bloodstream for about 7 days. After that the CL resorbs and progesterone levels plummet. However, in bitches that ovulate and don’t get pregnant, the CL hangs around producing elevated progesterone levels just as long when the bitch isn’t pregnant as it does when she is pregnant, which is 9 weeks or more.

Because of this elevated progesterone level the bitch’s uterus remains very fertile for over two months whether she’s pregnant or not. So in this fertile state, if she doesn’t get pregnant then other opportunists can invade the uterus and set up shop. And the bugs that do that are very nasty bacteria. This creates an extremely septic condition called pyometra.

Pyometras come in two forms: open and closed. An open pyo is one in which the cervix remains open and the pus that forms in the uterus drains out the vagina. This condition is typified by a dog with a smelly vaginal discharge and who acts like she has the flu. You’ll see lethargy, malaise, decreased appetite and sometimes vomiting and diarrhea. This can linger for days or even weeks before the client brings the pet in for help.

The other form of pyometra is a closed pyo, in which the cervix is closed. In a closed pyo the pus that forms in the uterus has nowhere to go, and so the uterus rapidly fills with this toxic pus. These dogs go downhill rapidly, eventually go into septic shock, and often die within 4-5 days of the onset of signs.

In either form of pyo – open or closed – the only thing that will cure them permanently is to spay them. In the case of a closed pyo spaying is necessary immediately to eliminate the source of infection. This means doing surgery on a critically ill animal. On the other hand, not spaying the pet means she will certainly die.

Pyometra surgery
This is a pyo in a small breed dog. There is no breed predilection for pyos. All unspayed females are at risk.

Pyos are extremely common. It’s been estimated that 50% of all the unspayed bitches aged 10 and older will develop a pyometra. The older the pet, the greater the probability of developing a pyometra. However, the disease isn’t exclusive to old dogs. The youngest dog I’ve ever diagnosed with pyometra was 8 months old, and I’ve seen several pyos in dogs less than 2 years of age. And how common is it? We do approximately two pyo surgeries a month. That means it’s extremely common. That makes pyometra the number one reason why I ALWAYS recommend spaying a non-breeding female.