This is very well done! Especially the face
I would like to recommend widening the "hips" a little bit. It looks slightly too small compared to a real horse's body.
I know the abdominals aren't completely polished yet, but it looks like you're missing out on a lot of that awesome flow that the muscles make, especially with that twisting motion.
I hope this helps
I'm excited to see this when its finished! Its definitely one of my favorites that I've seen so far.