Right now we have put nutridrench in their water and used vet rx.
It might be a respiratory disease such as MG or infectious bronchitis, and those are contagious. The others may be already exposed. Antibiotics such as Tylan and Oxytetracycline, and other antibiotics from feed stores are used to treat symptoms, although bronchitis is a virus that has to run it's course. These diseases make carriers of the whole flock. Testing can sometimes confirm which disease.