Shot 1 certainly has the cleaner composition without the wooden fencing getting in the way. However the problem (which is made worse with the cropping) is that the tree really is the main feature of the shot.
It dominates a large part of the photo and is also sitting on a good point of focal interest (look up the rule of thirds). With nothing surrounding the tree as well it really makes it take over, the horses end up becoming like the smaller trees, the fence and the field - they are background elements to the main subject.
something about the lighting on the horses is also jarring, esp with the far left and middle horses the horses themselves almost seem like they are clean "cut and paste" jobs. It might just be the local contrast over those horses and the fact that their angle gives them a strong shadow over their body - but they don't "feel" like they fit with the rest of the photo (including their own shadows on the ground).
A tiny bit of contrast reduction on the horses themselves might help to blend them in a bit more, but it won't replace the fact that, with the composition of the whole photo and the crop presented, the subject is very much the tree.
(ps don't take that to mean that the crop is bad, the crop itself is good, its just not highlighting the horses as a major subject component).