Estrogen May Generate Trouble.
A client asked me last week if, when we spayed her dog, we could just remove the uterus and leave the ovaries in. This seems more natural, like it may have benefits, but there are certainly drawbacks and risks. It's an unusual request so I called Dr. Memon, the reproductive specialist at the Washington State University Veterinary School to get the best advice. He said the risks are much greater than the possible benefits.
The ovaries would still produce estrogen. Spayed dogs are a little more likely to develop urinary incontinence in their golden years. They might leak a little urine while they're sleeping. Leaving the ovaries in may reduce this risk. That's about the only benefit.
She may not come into heat every six months, like a normal dog but estrogen would make her go into heat, produce the pheromones that attract male dogs, and even be receptive to breeding. She wouldn't get pregnant but the physical act of breeding may be risky and painful. When a dog is spayed, the cervix and a small "stump" of uterus are normally left in, and estrogen could have deleterious effects on them. Prolonged increased levels of estrogen can also suppress the bone marrow and result in a dangerously low red blood cell count.
A small piece of an ovary is sometimes inadvertently left behind when a dog or cat is spayed and the symptoms we usually see are similar to a mild heat cycle. It may also happen, though rare, that a dog or cat will be born with an extra ovary, or small bit of ovarian tissue. Either of these would be very unlikely to be spotted during a routine spay. Finally, other glandular tissue in the body that normally doesn't produce estrogen can sometimes, for some reason, produce estrogen or similar hormones that can cause dogs or cats to act like they're in heat.
There are two ways to find out if a dog or cat that has supposedly been spayed is still making estrogen. One is a blood test. We have to draw a blood sample, then give an injection that would stimulate ovaries if they were there, and then draw one or two more blood samples a specific time later. The samples are sent to a specialty lab and results come back in a week or two. The other option is exploratory surgery. The surgery is more difficult and more expensive than a routine spay because it is much harder to find a tiny piece of an ovary or make sure it's not there.
Dr. Memon sent me a copy of a case report about a dog that had been spayed as a puppy, and then seven years later developed enlarged mammary glands and a vaginal discharge. The doctor could feel a large mass in her abdomen, and laboratory tests indicated she was producing more estrogen than a spayed dog should. On exploratory surgery they found a large tumor. Microscopic examination indicated it was a type of ovarian cancer called a granulosa cell tumor.
These are the most common type of ovarian cancer but, of course, are normally not found in spayed dogs. The cancer usually does not spread, or metastasize and surgical removal is usually successful and results in a complete cure. Except that all that estrogen causes a host of other problems that can greatly complicate matters. The dog in the case report recovered, but I would guess the bill for all the things that had to be done came to several thousand dollars.
A routine spay is a lot cheaper and complications are rare.