Here is some more advise and pictures. Hope it helps.
My brother's mare Ginger had about 30 acres to run in a new paddock on the farm where we keep the cattle.
Of course the minute she was in there she ran to the one section of barbed wire and slid down it.
Here is what the wound looked like:
(yup, that is pretty much her foreleg muscle hanging out.)
We called our vet who is great and he gave meds and sewed the muscle back in there. They stitches came out and the wound was all gross like your horses' is.
Here is what my brother and I did (he works at one of the top Equine Hospitals, Rood and Riddle in Lexington, KY)
He gave her the max dose of penicillin, I think that it was 2x a day.
You would want to ask your vet, and know the weight.
(I suggest it ASAP, I have had horses my whole live and worked around them, and you need to get that if you are not using it NOW)
We gently hosed off the wound 2x a day and used a syringe with no needle to flush out the wound with some kind of antiseptic. You can use peroxide sometimes, but dont use it all the time.
You want it to heal and dry up and you do not want proud flesh (or flies it it)...After you let the horse stand and dry a bit, USE WONDER DUST if you have any proud flesh. The wound cannot heal correctly with proud flesh. The wonder dust is caustic and can deteriorate healthy skin also. You can spray some scarlet oil or some nitrofurazone on the wound and re-wrap it.
I like to let the wound air out a bit in between bandagings, so that some of that nasty stuff can get some air and scab up. You just want to keep the flies out of it.
***You can get cheaper bandages at a human medical supply centers. We were using lots of the absorbent pads and getting them from the feed store, they were 7 bucks each, and 3 for the vet wrap. Found the same stuff for less than a buck each at the Med supply store (where they sell wheelchairs, oxygen tanks, potty chairs and other first aid stuff)
Here is Ginger now!
Remember!
Penicillin!!!!!!!!
CLEAN and DRY! At least 2x a day!