A dog biting his tail can indicate either medical or behavioral problems. There are many reasons that dogs may bite their tails, many of them being medical reasons, so visit your veterinarian to eliminate medical causes before beginning a behavioral program.
Dogs and Allergies
The primary reason that dogs bite their tails is allergic reactions. Many dogs who suffer from allergies get hot spots right at the base of their tail. They bite the spot to try to relieve the itch, making the problem worse.
Allergies can be caused by fleas or other mites as well as diet or environmental stimulus. It's often difficult to determine the cause of the allergies, but flea medication can eliminate any fleas, and there are many products on the market designed to relieve the pain and itching of hot spots.
Other Medical Causes
Dogs also may bite their tails if they are suffering from problem bowels. Many dogs bite their tails if their anal glands are impacted, which can be a clue it's time to take your dog to a groomer or vet tech to perform the task. Your dog may also bite his tail if he is constipated or has painful diarrhea that is making him uncomfortable.
Neurological Causes
Though it's rare, many dogs can develop neurological disorders that cause them to exhibit strange behaviors. One manifestation of this is a tail chasing or biting routine, which dogs may do periodically, especially when stressed.
There may be a training component involved in this behavior, but it can't be fixed without consulting with your veterinarian. Medication or additional surgery may required as it could indicate a larger health problem.
Kennel Syndrome
Many dog learn to chase or bite their tails out of boredom. This begins when under exercised adolescents desperately need to release built up energy and stress and begin to chase or bite their tail when it catches their eye.
This is often referred to as "kennel syndrome" because it frequently happens to dogs in kennels. Because they spend so much of their day in a tiny cage with barking around them and people walking through, they have a lot of pent up energy and frustration and thus must release it the only way they know how.
Training New Behaviors
If medical causes have been eliminated, you must focus on training away the behavioral component of the tail biting. In fact, even if it began because of a medical cause, the behavior could still become a habit even after the medical cause is cured and require training.
Begin your dog on a new exercise program. Ensure that he is getting more than the appropriate amount of exercise so he will have no desire to chase his tail. This involves at least two 40 minutes sessions of full blown running daily, not just walks. Take your dog running or play fetch.
Then, teach your dog an alternate behavior, something that he can do instead of biting his tail, such as going to a spot to lie down. Teach this behavior when he is not biting his tail so that he knows how to do it on command.
Once you see him beginning to eye his tail, give him the command. Reward him profusely for listening. In the early stages, it may be appropriate to keep him on leash so you can lead him to the spot if he can't do it.
Soon, the new behavior will replace the tail biting behavior as your dog's default behavior. When you catch your dog heading to the spot on his own rather than biting his tail, reward profusely. He's on his way to conquering his habit!