Horse breeders are popularly recognized as experts of animal husbandry. Through experience and study of pedigrees, horse breeders select horse matings to produce superior performance horses.  Nowhere is this reputation stronger than among breeders of Thoroughbred race horses.  Over 350 years ago a group of essentially 100 horses founded the breed.  From this genetic base, the breed has been crafted by breeders through selection to produce the modern race horse.  
 

Yet, despite 350 years of selection, recent studies suggest that as much as 30% of racing performance is determined by genetics.  Seventy percent of performance is management and training but the edge in a race may be genetics.  Considerable genetic variation still exists for racing performance. So what does this mean?   First, we can still use genetics to craft better horses. Second, more than one speed gene exists. 

This not a surprise.  Horses of all sizes and types win races.  Secretariat was a large horse 16.2 hands while another noteworthy race champion of the 20th Century, Northern Dancer, was only 15.2 hands tall.   Man O War had a stride length of 28 feet while a more current Kentucky Derby winner, Smarty Jones, had a much shorter stride length.  There are many ways to win races.