I love the detail.. and the way the mane and grasses play together , as said above.. my only problem , is I want the Horses Feet!! and IMO , I think I would crop a lot off the top.. The objective of this composition, and subject solo, is the horse!! I would crop somewhere just above the horses head..
My basic impression of the picture is that it has mixed styles - inadvertently. The overall impression is of a pastoral open scene - sweeping views, wind-blown hair, animals - but that implies traditional views of the contents - whole animals, traditional interaction with the animals.
Then a couple of things interrupt that - the strange eye-look from the animal, the cut-off muzzle making an interesting abstract with the line of the back, the cut-off legs.
(Without mentioning the excess non-contributory space at the top)
I don't think there is a real path to make this really successful because you can't add the legs and the muzzle. You could crop it to get a reasonably interesting small image