I have a Boston terrier/border collie mix spayed female that is obsessive about licking her butt. I have spent hundreds on vets, groomers, & trainers, who have ruled out worms, anal glands, parasites,and digestive problems. The dog is healthy, her poop is normal, and there is no swelling or redness. Whenever the dog relaxes, though, she will start licking her butt, and won't stop until someone commands her to stop licking.
My roommate cannot accept the butt licking. She says I have to keep taking the dog to other vets until one of them solves the problem. I can't afford more vets, or more ineffective products. Why does my dog keep licking her butt if vets cannot find a cause for it?
For some dogs licking/chewing/biting a certain body part becomes an OCD. There may have been a problem initially and the dog got satisfaction from the resultant behavior and now just does it for no medical reason. It has become a behavioral thing now and probably the only way to break the habit is by rendering the area she is biting inaccessible. You could purchase an ecollar and keep it on her 24/7 for a few weeks to see if that will break the cycle. If there truly is no medical reason for her doing it, then anti-compulsive/anxiety drugs may need to be given to her to stop the behavior.