 American Thoroughbred races are run at a wide variety of distances, most commonly from ; with this in mind, breeders of Thoroughbred race horses attempt to breed horses that excel at a particular distance (see dosage index).Horse racing in the United States and on the North American continent dates back to 1665, which saw the establishment of the Newmarket course in Salisbury, New York, a section of what is now known as the Hempstead Plains of Long Island, New York.This first racing meet in North America was supervised by New York's colonial governor, Richard Nicolls.