Christopher,
love the subject matter. As you already mentioned, shooting at mid-day creates some pretty harsh lighting and very deep shadows. Your first image shows that pretty clearly.

I love the B&W treatment. The composition is good and it lends itself very nicely to B&W conversion. However, the vertical lines are not straight up and down. That's a small point but I'd keep that in mind when you're doing post-production. Always make the straight lines run at 90 degrees to the sides and top/bottom of the frame.

Overall, I like the fact that you shot these from a low point of view. I like Image #2 as well but for me there's a bit too much foreground grass that doesn't do much compositionally. I don't like the rear view of the horse -- but that's a personal preference. I don't like rear views of any animal unless you're really trying to show something off like a great rear movement going away. The movement shot is nice but I wish you were closer and had cleaned up the background wires.

I think you should give this another try either early in the morning or late in the afternoon to get some better light. And try tighter framing. We know that horses graze in pastures. Unless the pasture is absolutely gorgeous, let's see more of the horse.

Good start.

Jim