Nasty lol. But I have seen much worse.
I personally think winter is the best time (if there is such a thing) to get wounds like this. As you don't need to worry about flies and dust and such getting in there....less chance of infection due to insects.
Clean it out w/betadine scrub or other antiseptic. I personally would have got it stitched, but seeing its been more than 24hrs, that wont be possible now.
Keeping it clean is the most important thing. You may want to give your horse some penicillin for the next 3 days or so (if your comfortable giving IM shots) if not Tribrissron (sulfatrim) is effective too, this can be fed orally in feed.
Is your horse up to date on Tetanus?
With it being on the hip wrapping it wont work, but its better to leave wounds open if you can. They do tend to heal faster, and less chance of gauze/bandages pulling off healed flesh from dried blood etc.
There is a product called CUT HEAL...its just like it sounds, heals cuts...but from the inside out, so it doesnt promote proud flesh, and it encourages hair regrowth.... I love the stuff. Works great!!