Murray's liver chestnut Australian Quarter Horse. A red roan, Quarter Horse mare. Some horses of Quarter Horse lineage carry more than one splash mutation. In February 2008, Burns registered as a lobbyist for the American Quarter Horse Association. He owns an American Quarter Horse named Smokey. The American Quarter Horse has also been exported worldwide. One example of this is the American Quarter Horse. Tennessee Walking Horse, and the American Quarter Horse. It is classified as an illegal "Class I substance" by the American Quarter Horse Association. The British American Quarter Horse breed society is the AQHA-UK. This disease is usually seen in Quarter Horse foals and is fatal. As a result, more Thoroughbred blood was added into the developing American Quarter Horse breed. The ancestors of the Quarter Horse were prevalent in America in the early 17th century. The historic racetrack reopened on November 28, 2009 but only for Quarter Horse races. The American Quarter Horse is the most commonly used horse breed.