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. The breed standards of the Australian, American and Canadian kennel clubs specify that the Australian Cattle Dog should have a natural, long, un-docked tail. There will often be a solid colour spot at the base of the tail and a white tip. It should hang in a slight curve at rest, though an excited dog may carry its tail higher. The tail should feature a reasonable level of brush. The Australian Cattle Dog thrives on change and new experiences, and many handlers find training the breed challenging for this reason. 'Canine Breed-Specific Risks of Frequently Diagnosed Diseases at Veterinary Teaching Hospitals' (PDF).