The Rat Terrier is an American dog breed with a background as a farm dog and hunting companion. The Rat Terrier ranges from about 10 to 25 pounds and stands 10 to 18 inches at the shoulder. After a period of development this line resulted in the American Hairless Terrier, recognized as a separate breed by several registries. Ear carriage is erect, but can also be tipped, or button, all of which contribute to an intelligent, alert expression. The tail has been traditionally docked to about 2–3 inches, but the bobtail gene is very common in Rat Terriers and can result in a variety of tail lengths. Today, some breeders prefer a natural, undocked tail, which is accepted in the breed standards. Rat Terriers were accepted into the AKC's terrier group June 2012.