Unspayed dogs face increased health risks later in life

When Maya was young, her owner thought he might let the big Rottweiler have a litter of pups. I gave my spiel about pet overpopulation, and the increased risk of mammary and uterine cancer as well as urogenital infections in unspayed dogs, then launched into my spiel about responsible breeding. So when Maya was four years old, we took radiographs to evaluate her hips for dysplasia. We discovered her conformation wasn’t great, making her a dubious candidate for breeding. It seemed she might be infertile anyway, as her heats were erratic and unusually mild. “You should have her spayed,” I suggested regularly.

But somehow the years slipped by. Maya had a bout of tick-borne disease, an unfortunate encounter with a fishhook, a case of “dry eye,” but she remained unspayed. More time passed. Now she was an old lady, with an old lady’s share of lumps and bumps, not surprisingly including several in her mammary area.

Spaying a dog before their first heat reduces the risk of mammary tumors to less than one percent compared to intact females. After one heat, the odds are eight percent. After two heats, 26 percent. By the third, spaying does not significantly reduce the incidence of mammary cancer. The good news is that as many as half of canine mammary tumors are benign. Due to her age, and the reasonable chance the masses were benign, Maya’s owner opted against surgical removal, and since it seemed silly to make a fuss at this late stage, I lightened up about urging him to spay her.

Then this July, during that awful heat wave, Maya started drinking and urinating excessively. At first, her owner didn’t think much of it. It was so stinking hot, of course she was drinking more. Then her appetite waned. “She’s barely eaten for a day and a half,” he told me. “Though she did eat a biscuit from the bank.”

I examined her. Temperature, weight, heart, lungs, all fine. Abdomen — well, at almost 100 pounds, she was too big for me to palpate much. I advised blood work and a urinalysis. Excessive urination and drinking are technically called polyuria and polydipsia, abbreviated as PU/PD. A chemistry profile would help evaluate for kidney failure, Cushing’s disease, diabetes, and other metabolic conditions that cause PU/PD. A complete blood count (CBC) would determine if she was anemic, or if there was an infection lurking. A urinalysis might reveal a urinary tract infection, and give us other useful information. I sent Maya home on broad-spectrum antibiotics, pending test results.

Back in the lab, I noted that the urine was pale, almost straw color. Using a refractometer, I checked the specific gravity. The urine was unusually dilute, almost like water. After spinning the sample in the centrifuge, I poured off the supernatant, added stain, then examined this sediment on a slide under the microscope. (If you don’t know supernatant from precipitate, go back to high school chemistry class!) Not much exciting. None of the inflammatory cells expected if this was a simple urinary tract infection.

Moving on to blood tests, her kidney, liver, blood sugar, and electrolytes were all normal. She was mildly anemic. Her white blood cell count was moderately elevated. Hmmmm. I put on my thinking cap. She was the right age range for a splenic tumor. That could cause anemia. She might have pyelonephritis — an infection up in the kidneys. She might have… Oh, drat! She might have a pyometra.

Pyometra literally means pus-filled uterus. When a dog goes into heat, the cervix relaxes to allow sperm to enter. Sometimes bacteria can invade instead. In older unspayed females, long-term hormone influences cause a pathological change in the uterine lining called cystic endometrial hyperplasia. This abnormal uterine lining is especially conducive to bacterial growth and massive infection can result.

Pyometra usually occurs one to two months after a heat cycle. If the cervix remains open, pus may drain from the dog’s vulva, but if the cervix closes, purulent material stays sequestered inside. The uterus can become extremely distended with pus. Toxins and bacteria may leak into the bloodstream making the dog extremely sick, the uterus may even rupture, but clinical signs of pyometra can be fairly nonspecific and vague, especially in the early stages. Symptoms may include depression, lethargy, poor appetite, PU/PD, vomiting, abdominal distension, vaginal discharge, and/or occasionally fever.

In some cases, the enlarged uterus can be felt by palpating the belly (taking care not to press too hard and risk a rupture), but radiographs, or even ultrasound, are often required for definitive diagnosis. Laboratory abnormalities may include anemia and elevated white blood cell count, as noted on Maya’s tests, as well as others we didn’t see with our patient, such as kidney dysfunction, low blood sugar, and electrolyte imbalances.

Pyometra is a life-threatening disease, especially if the cervix is closed. Recommended treatment is immediate surgical removal of the infected uterus. Risks of surgery include rupture of the pus-filled uterus into the abdomen, peritonitis, sepsis, kidney failure, disseminated intravascular coagulation, even aspiration pneumonia. The surgery can be difficult, and expensive, usually requiring several days of hospitalization.

Occasionally, if it is a valuable breeding animal, medical management with antibiotics and hormones can be attempted, but this is risky, and the problem tends to recur with each subsequent heat. Reviewing Maya’s previous history, I noted she had experienced similar symptoms last year and had recovered with oral antibiotics. This year seemed worse. Without definitive diagnosis by X-ray or ultrasound, I couldn’t say for sure, but pyometra was certainly a possibility, in which case, her life was in danger. As is often the case in veterinary medicine, age, prognosis, other ailments, and finances all had to be considered when deciding whether to pursue further diagnostics and surgery.

For now, we are hoping it’s not pyometra, and that she will again respond to medical treatment. But her case is a cautionary tale about some of the serious problems that may affect an unspayed female dog.