If a vet is at all possible, including farm or large animal vet, it would be best to get antibiotics for the specific problem. Almost no antibiotics are approved for poultry because of egg and meat withdrawal times. But if you need to treat a serious infection most vets who agree to see you will help you. Bone infections from bumblefoot should not be assumed without a vet. Doxycycline will not treat osteomyelitis. Clindamycin or cephalosporins may treat it, but may be hard to get or be prescribed. We are not vets here and cannot diagnose osteomyelitis. Bumblefoot, though is pretty common. Usually soaking and removing pus may be enough, and some may use amoxicillin to treat it.