The Australian Shepherd, often known simply as the 'Aussie', is a medium-sized breed of dog that was, despite its name, developed on ranches in the United States during the 19th century. An Australian Shepherd enjoys working, whether it is learning and practicing tricks, competing in dog agility, or engaging in any other physically and mentally involving activity. Not all homozygous merles are affected, but most are, making the breeding of two merles a very touchy subject. Some breeders euthanize mostly white pups, while others may attempt to sell them as 'rare' white Aussies without disclosing the potential for health defects. A large percentage of homozygous merles sold eventually end up in rescue and shelters, as the average family is ill-prepared to take on a deaf or blind pet.