Several things to try to improve this image. Shoot when the horse is looking toward you. Don't center the horse in the middle of the frame. Shoot earlier or later in the day when you get some shadows to add the third dimension to your picture.
Sorry, very plain, very simple. A closeup with one horse in the first plane, the second approaching, from a slightly towards the right position would have made a more powerfull photo ( even if not wide-angle material ).