We had a sheepherder come by our place once--grazing on the range. He left behind a ewe that was nearly dead. She couldn't walk because the maggots had eaten into her leg. He left her for dead. (Really irritating that he'd just leave her to die near our house!) Probably she was torn by a coyote. The gash was about 6" x 4" and then bottom and top were farther in than your fingers could reach.
So I took some hydrogen peroxide to it. I washed her wound time and time and time again with the hydrogen peroxide. It was deep and a huge gash with the skin all loose and all kinds of maggot poison (yellow) in it and at least a finger's length under the skin where you couldn't see anything. As I poured it on, the maggots died like they were already dead. The ones that were wiggling, one dose of hydrogen peroxide, and that instant, they didn't move again. I washed her way up inside with the peroxide, rinsing and rinsing until no maggots came out. It took about an hour, and it was really sickening. I cleaned out the dead muscle (they had eaten her) and we kept it covered with a vaseline-like substance to keep the flies off. They didn't want to go back on anyway since the taste of hydrogen peroxide was not to their liking. About a week, and it was healing just fine.
I think we also gave her a shot of penicillin and one again the next day. The vet said we'd probably lose her. Everybody told me to just shoot her because she would die. And the sheepherder gave her up for dead.
He left her for dead. But she didn't die. She lived. We took her to the sale about three months later, and she brought a good price. Nice ewe if you like sheep.
If you use this stuff, don't continue to use it after you get the wound clean unless there are maggots in the wound (then you didn't do a good job). Hydrogen peroxide keeps a wound open and slow to heal. You don't want to keep using it. Great for infection too.