A couple of horse anatomy notes:
A horse's eyes are positioned to their sides and their brow ridge is hardly there. (common mistake that results in a lot of dog-like horses)
They have a ton of mass in their core, so I repositioned the legs to be closer together to better convey this.
Removed a couple of pixels on their hooves to make the legs appear less stiff

Though, there is another problem of the size of the head. Making it shorter would make it look less out of place at this scale, but it starts being harder to read as a horse.