Happy New Year to all you Derby fans and Happy Birthday to all the race horses in the northern hemisphere. In the northern hemisphere, every Thoroughbred's birthday falls on January 1, regardless of what day of the year they were actually born. Most Thoroughbreds in the northern hemisphere are born between January and May, which is why a spring drive through Kentucky horse country rewards you with scenes of grazing mares and their foals. This means that the some of the 3-year-olds who run in the Derby might not be quite 3 years old. This practice has been going on since the earliest days of horse racing to make it easier to condition races and keep horses with their age group, particularly back when there were few good records about horse births. In the southern hemisphere, the standard Thoroughbred birthday is August 1, when its breeding season begins. So no matter who your favorite Derby horse is, if they were born in the northern hemisphere now is the time to wish them happy birthday. The above photo is courtesy of Taylor Made Farms.