Unpopular opinion (please don't hate me.) If an animal has the will to live (you can tell if you pay attention) then you shouldn't put them down. That means they don't want to die yet even if their injury or sickness is terrible (my one exception for this is if it's an extremely contagious disease that doesn't get better.) I had a chicken named Sasha who got a massive hole ripped into her side by dogs but she managed to fly back out of the dog pen and was sitting slightly hunched in the yard when I found her. I had to get the net out and chase her down in order to figure out what was wrong! No one thought she would survive but since didn't want to die we tried treating her. She healed completely!
Apple Cider Vinegar. To really be worth something, it has to have the "mother," which is the culture that does the fermenting. Braggs is a brand that a lot of stores carry now, that has the mother in it. I've seen it in TSC, and our local big grocery chain, Meijers.
Frankly, I use my own kombucha tea instead of ACV.