The occasional odd ones...

As a vet one of the worst things you'd like to hear is: "You know what Doc? That Dog you sterilised? Well...she's pregnant!!" Hahaha! Well, when that happens you know you better change job...
Nothing like that happened but today I was brought a dog who was sterilised by a colleague...but came on heat again and was mounted by numerous males! The owner was totally out of himself; threatening to sue the vet etc...
Okay...Can a spayed bitch come on heat again? Technically the answer is NO. We do perform ovariohysterectomies here and both ovaries and uterus are removed. So how come that animal was on heat again!?!
The ovaries are located at the ends of each uterine horn and are suspended on ligaments to the abdominal wall. They are inside a bag-like structure and more often than not,embedded in fat. During the surgery the vet has to pull hard to get the ovaries out and relax those ligaments. The blood vessels are ligated and the ovaries excised.
Depending on the place you ligate, you might leave a small portion of the ovary inside and this ovarian tissue can grow and continue to produce the female hormones to make your dog "feel sexy" Usually, this happens when the vet is not confident enough to apply adequate traction to loosen the ovarian ligaments to allow a full view of the ovary.
Then there is one very interesting phenomenon call "ectopic ovarian tissue": this is when small islets of ovarian tissues are found disseminated around the actual ovary and if you remove the ovaries , the ectopic ovarian cells take over and produce the necessary hormones to bring the animal on heat again.
So ...hmm... this does happen...1 in around 10,000 have various ectopic tissues. Since the uterus was removed...there is absolutely NO RISK of pregnancy...Just the hassle of having a pack of overexcited "fiances" who will come uproot your Geraniums, wake up your neighbours, urinate on your car tyres and mess up your veranda.In the long run, you can choose to regularly suppress this residual ovarian function with hormonal injections.
So bear with your vet, there will be that occasional odd one that can make him look like a total bluffer and you should not lose trust in him/her for that.
Aaaaahh! Those exceptions that make you appreciate the rules even more...gotta love them!