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 was developed for its ability to encourage reluctant cattle to travel long distances and may be the best breed in the world for this work. However, some working dog trainers have expressed concern that dogs bred for the show ring are increasingly too short in the legs and too stocky in the body to undertake the work for which they were originally bred.