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 colour 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. The Australian Cattle Dog is a sturdy, muscular, compact dog that gives the impression of agility and strength. It has a broad skull that flattens to a definite stop between the eyes, with muscular cheeks and a medium-length, deep, powerful muzzle. The ears are pricked, small to medium in size and set wide apart, with a covering of hair on the inside. The eyes are oval and dark, with an alert, keen expression. The neck and shoulders are strong and muscular; the forelegs are straight and parallel; and the feet round and arched, with small, sturdy toes and nails.