My chicken broke its foot now it's swollen.
This was a post I got from an old thread... Hope it helps and your chicken is ok!!
You want to treat at a rate of 25 mg. per lb of body weight. Or approx. 1 baby aspirin per 3 lb's. I crush them between two spoons, add a couple cc's of buttermilk and suck it all up into a needless syringe and dose the bird that way. The buttermilk also helps buffer the aspirin.
Aspirin is a good anti-inflammatory but it is also a strong anticoagulant so be very careful to watch out for bleeding if you do use it. I'm not sure if the benefits outweigh the risks.
Personally I would splint it, but if the bird is weight-bearing on it then I'd leave it be. Keep it isolated to reduce its movements. Nice high protein food to help with healing :)