Dogs with normal foot physiology have four toes on the hind feet. Some breeds possess a fifth toe on the hind foot, commonly referred to as a dewclaw, but more accurately called polydactyly. Normally located higher up the leg from the other toes, it may or may not come into contact with the ground when the dog runs and plays.
An Evolutionary Throwback
Dogs normally considered to be "flock guardians" present an extra hind toe or dewclaw most frequently. These breeds would include the Anatolian shepherd, Australian shepherd, rottweiler, shih tzu, standard poodle, and many Asian breeds including the shiba inu, akita, jindo, sasparee and Korean tosa. The great Pyrenees is the most commonly known polydactyl canine, and may even present six hind toes. The Norwegian Lundehund may present five toes on both his front and hind feet. In a study supported by the Korean Research Foundation and the Korea Science and Engineering Foundation, scientists came to the conclusion that the presentation of a fifth toe, most accurately called polydactyly, is a reversion from the evolutionary loss of the toe.
Caring for Dewclaws
A polydactyl dog's dewclaw may be attached by bone or solely by skin. Dewclaws may be removed surgically to prevent them from getting caught on objects, which can cause injury to the dog. If not removed, the toenail should be trimmed regularly to prevent it from causing sores or other injury to the rest of the leg and foot.