First off, this is a very pleasing image. I like the sense of tranquility created by the whole scene. I can imagine sitting in the grass on a cool evening just watching this guy wandering and grazing. I'm not usually a fan of horses in general, but this is well done and would have garnered a 6 from me had I voted. I think for the DPC masses, a 5.76 is a very good and appropriate score for this shot.
If I were to try to improve the score, there are a couple of changes I would make. First, the horse is obviously the center of attention, and the surrounding area helps set the mood, but it is a bit distracting in a couple of places/ways. I would recommend cropping out the brighter grass at the very bottom of the image and cloning out (or not including in the first place) the black rectangle in the water on the left. Your processing looks really good except for the (to me) overly saturated yellows. This shot would probably look really good as a B/W or duotone even.
Overall, great job!
Please feel free to shoot me a PM if you have any comments or questions.
Nathan