Well, because chickens lay eggs, most medications and antibiotics are not approved. Tylosin is one that is approved in the US. But I never tell people to use an antibiotic unless they know what they are treating. A small amount of antibiotics can be found in the eggs for a couple of weeks after using them, and you certainly don’t want to eat them or contribute to antibiotic resistant bacteria. So, it is always good to help build up their immunity, and let them fight off things naturally.