Cool, dynamic shot. I love to go to the races and photograph those beautiful creatures myself. I like your picture a lot, although I would have zoomed in on the horses and leave out the people in front. But the way you did it, the image has more layers and colors, so it's fine just the way it is.
Nice photo, I agree with all of the above comments. If I could suggest anything it would be to use a circular polarizer...it would've made the clouds more defined and less over-exposed.