That could be a tabloid headline, though I guess it's pretty tame compared to "Elvis sighted in laundromat!" or "Politician actually admits lying!". The point is that it's weird — dogs who have been spayed have no uterus and no ovaries, so how could they still be having estrus cycles and coming "in heat"?
Once upon a time, about 28 years ago, I spayed a Scottish Terrier. She continued to have heat cycles, and I was mystified (not to mention mortified). That is NOT supposed to happen.
Now, I have to tell you: when you're performing an ovario-hysterectomy on a dog, sometimes it's pretty hard to pull the ovaries up out of the abdominal cavity. If you're not careful, you might cut things a little close and leave some ovary in there. When you've cut things off, you need to inspect what you removed and be sure the whole ovary is there (plus a little extra tissue, just to make you feel good about getting 100%).
If you leave some ovary in the dog, they will continue to cycle regularly, coming in heat every six months. They won't get pregnant, since you've removed the uterus, but they still come in heat, they are still at greater risk for breast cancer, and could even have "female trouble" developing pyometra in the stump of the uterus.
Sometimes, you cut things pretty close, but in the case of the above Scottish Terrier, I recalled vividly that there had been no problems at all. It was not a "close call". So, I called the reproductive specialists to ask what I needed to do. Now you could run hormone assays to see if there is functional ovarian tissue left, but if the dog is coming in heat every six months, you can be pretty sure there is functional ovarian tissue.
Here's the problem: it could be a piece of ovarian tissue the size of a pin-head. The specialist told me that I could even have implanted some ovarian cells on the body wall by rubbing the ovary against it on the way out. "Jeez, how am I going to find that?!" He told me to wait until she was sure enough in heat (flaming) and do an exploratory. Look for a little tiny red thing that looks like ovary. It could be anywhere — the proverbial needle in a haystack.
So, what happened, you may ask? The owners asked, "Can she get pregnant?" and when they found she could not, they refused to allow the exploratory (even at my expense). They decided to just live with it, and the dog lived a long and happy life, despite cycling every six months. So, I'll never know if I could have found what I needed to.
This is Tinkerbell. She was spayed at six months old, and at seven years old has had heat cycles every six months. And really, lately she hasn't been feeling all that great. Several years ago, I told her owner what it would take to look for the little tiny piece of ovary and she decided not to do it. Lately, though it had started to bother both Tinkerbell and her mom more and more, so she said, "We'll do it the next time she comes in heat."
I must say that I had some misgivings. I had told Mom that I wasn't sure I'd be able to find what we were looking for, even with the dog in heat. It could be so tiny. And it could be anywhere in there… I thought.
What I had not counted upon was that whoever did her surgery did an incredibly lousy job… unbelievable, really. This picture shows a piece of ovary on the right, removed from the usual ovary location. On the left, also attached to a usual ovary location, we have an entire ovary, which you can't see because it's behind that big thing that looks like a Vienna Sausage. The "thing" is a section of uterus that is full of pus, sort of a pocket-sized pyometra. It was bigger than her kidney or her colon, and when I first looked at it, I couldn't imagine what it was. It just didn't occur to me that a surgeon could have left that much uterus in place.
So, while it was hard to believe, it wasn't all that hard to find. I sent the tissue off to the pathologist, thinking it must be a tumor or something, but it wasn't. "Ovary and uterus, filled with pus". The good news is that Tinkerbell feels better than she has in a long time.