The Australian Cattle Dog (ACD), or simply Cattle Dog, is a breed of herding dog originally developed in Australia for droving cattle over long distances across rough terrain. This breed is a medium-sized, short-coated dog that occurs in two main color forms. It has either brown or black hair distributed fairly evenly through a white coat, which gives the appearance of a “red” or “blue” dog. Australian Cattle Dog has been nicknamed a “Red Heeler” or “Blue Heeler” on the basis of its coloring and practice of moving reluctant cattle by nipping at their heels. Dogs from a line bred in Queensland, Australia, which were successful at shows and at stud in the 1940s, were called “Queensland Heelers” to differentiate them from lines bred in New South Wales; this nickname is now occasionally applied to any Australian Cattle Dog.