I had a chicken that survived a dog attack and lost a big piece of her back skin (about 3x3 inches). I am not for doing anyone in (no one goes to freezer camp at my house!). I gave her aspirin in water: five 325mg tablets crushed and dissolved in one gallon of water. She was to only have that water. She seemed comfortable (poor thing!).
I also used indigo Wild's Zum frankincense and myrrh spray ONCE. It smarts (at least on me) for about three seconds, then just feels a little warm, then after than, no pain but speeds healing and prevents infection (kills bad bacteria and fungus). (Realizing we are about chickens--you can use the Zum on any species EXCEPT cats. Horses, dogs, chickens, me... we all have benefited.)