This just floored me when I browsed through "critiqueable". I couldn't believe it was a photomanipulation--I thought it was some happy accident of nature.
Originality, technique, and impact are just full marks. The margin and the spacing, the area of breathing around the focus of the image, the impact are all amazing.
The only thing I'd suggest is maybe adding a bump near the back for the tail. Also, I think the nose of the horse needs to be a little bit longer and flatter--it took me a few seconds to figure out what was "off" about the picture before me.
Once again, great job!