Anebel... if they're caring for that horse and cleaning out the wound (not cleaning it so that it's bleeding again) every few days, plus keeping a large bandage on it, it most likely will not get infected. Also, there are a large amount of brands of wound cleaners and healers that help speed up the process, help create new skin, and even hair.
I think that a lot of you guys are overreacting. This COULD happen to your horse. I do not know the FULL details... but I do know what happened. The owners didn't leave the horse out in a field for several years, allowing it to grow worse. Instead, they took the horse (that they obviously couldn't care for anymore) to a rescue, wanting the best for him.
It wasn't as much a matter of bad care and "abuse" or "neglect", but it was a case of a horse that got into a BAD scrape. By blaming the owners, you're blinding yourself to the fact that the horse needs help. And it's now getting it.
Note my name: FutureVetGirl. I want to help animals through a Vet career. Rescues mainly. I'd have to deal with cases like this, or similar to this most days. I can't begin yelling and saying "THIS OWNER IS STUPID, HE HAS NO RIGHT TO EVEN OWN A HORSE". I have to help the horse first off, and then look at the situation. It's apparent that the horse is getting help. And the situation is that the owners DID get the horse help. Even if it meant losing their horse.