It really is a matter of weighing the horse's discomfort v. survivability. If he is on heavy pain killers, which it sounds like he is, and he gets worse... its not fair to the animal to put him through the extreme pain. That is really what the owners and Doc have got to weigh. They knew this when they tried to save the horse in the first place. An animal that does not have a clue what is going on cannot be allowed to suffer unduly... No matter how bad we all want him to live.