This absolutely, for sure, your best that I've seen! Excellent work! I can tell you've paid attention to my comments on the previous two pieces.
Your proportions are looking great. Check them on the legs that are vertical but I think they are looking good.
Your addition of the darker shadows is very effective for depth. I would still like to see more detail done in the joints however. You might also consider lightening up some highlights even farther. Let them go even close to white.
One little thing on the hooves. The front and back sides of the hoof should be parallel. You have got a slight opposite slant going in them. Otherwise they are fine.
I don't have much else to say. You might be able to add a bit more depth with shadows and highlights to your background scene but I'm not sure how. You'd have to work that one out yourself.
Really, again, very well done! I'm soo excited to see all the progress you have made within these three pieces. Keep it up!