For me neither photo had a lot of impact. Both were well shot, and well framed, but the composition didn't improve the photo for me. (1st photo) It's such an action filled photo, and the direction of the horse appears to be traveling toward the right side of the frame, but it's immediately cropped off. For me i would have liked to have seen the photo landscape, so as to give the horse somewhere to go! the sky causes or eye to wander. also the slight off axis of the photo is a bit deterring.
(2nd photo) very much the same as the first, it's a lovely shot, and the look on the horse is soo intense! but its looking so hard at the right side of the image, i felt it would have been lovely to again, give it somewhere to go, let the people who are looking at this photo see what the horse is so intent on! perhaps its covering some ground as quickly as possible, or another pole.
Just so you know, both shots were beautifully timed, perfectly focused and exposed. It was just their overall composition that i would play with! With sport photo's they can so easily just be "another sport shot", play with the composition to make them "that amazing sport shot" vs. just another in the fray.