Compulsive Licking, Biting, and Scratching in Dogs - Pets WebMD

When mental acuity diminishes, dogs may engage in more repetitive behaviors such as tail chewing
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Injuries to the tip of your dog's tail are common. Some dogs chew on the ends of their tails out of nervous agitation, or due to fleas or dry skin.
Dogs chews his tail - posted in Health and Genetics: My dog has lately got into the habit of chasing/chewing his tail
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If your dog suddenly starts chasing or biting at his tail, you should schedule a veterinary visit. Dogs will chew at a painful area much like people rub an arthritic knee to provide relief. For example, dogs that get their tails caught in a closing door or nick them on a sharp object will chase and chew at their tails to soothe the injury. Nov 30, 2009 - Where is she chewing? Is she chewing the base of her tail/back area? Paws? Food allergies are a common cause of severe scratching in dogs.
Photo provided by FlickrSome dog tail injuries, like botched cropping and lacerations, can take a long time to heal, due to your dog's urge to chew and bite at the wound
Photo provided by FlickrTail Biting in Dogs -- What Are the Causes? - Dogster
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A degree of tail-chasing isn't out of the ordinary for dogs: When they feel exuberant and lively, they might let off some energy by chasing their tails. If you notice your dog persistently chewing the base of the tail, however, you should take action. Incessant tail-chewing can signify a medical problem or an obsessive behavior that leads to wounds and infections.Flea allergies can cause dogs to gnaw at the bases of their tails. Likely, more fleas are lurking just above the tail on the lower back, where the dogs can't reach. They might chew at any part of the tail in chase of fleas.Anal sac impaction is often behind dogs chewing on the bases of their tails. Canine anal glands function as territorial scent markers and lubricant for elimination. When anal sacs don't properly empty themselves, they can become impacted. Anal sac impaction is highly uncomfortable; it itches intensely. If you notice your dog obsessively chewing on his tail right by his derrière, he could be trying to minimize the discomfort he's experiencing. Another common sign of anal sac impaction is scooting. If you spot your pooch dragging his behind around on your living room floor, anal sac impaction is suspect No. 1.Games and stimulating new dog-friendly toys can also frequently minimize or do away with obsessive tail chewing in dogs. If you need effective suggestions, speak to your veterinarian or to a trusted animal behavior expert.If your veterinarian determines your dog's tail chewing isn't a medical problem, he'll consider behavioral causes. Giving your pet more exercise often solves compulsive chewing behaviors. Ample exercise is particularly vital for dogs of breeds historically raised to work in tasks such as digging and herding. When these dogs don't receive sufficient exercise, it takes a toll on their mental health and leads to compulsive behaviors such as tail-base chewing, obsessive scratching, aggression, rough play and excessive barking.When Scruffy defecates, normally the two small glands found just inside your dog's rectum secrete a thick, oily secretion. However, a time may come when normal defecation is not enough to empty those sacks. Soon, the anal glands become impacted and uncomfortable. The bottom line is your dog may chase his tail and chew his bottom in an attempt to empty those sacks. Take him to the vet who can express the glands and even show you how to do it in the future.