Good. Take a careful read and absorb all the ins and outs of different approaches. My birds, purebreds, have never showed any symptoms with the exception of 1 that was in direct contact with an infected flock. Resistant or not, wont you get sick if a sick person sneezes in your face? I desire a healthy flock so I see Denagard as a ray of hope to that end. Once a month they get a 3 day drink of it. Chicks get a dose too in the first week. If symptoms appear in the one I keep separate he gets Oxytetracycline + Denagard, however I believe he has permanent damage due to lesions- this translates as CARRIER. Look for mild wrinkling in the ends of eggs, and thin shells, and a drop in egg laying is suspect too. Again, these are signs of permanent damage due to lesions and translate as the bird being a possible carrier.
And by the way, I was that awesome little villain for a large part of my life...its not what its cracked up to be, I enjoy my freedom too much, real villains are mere slaves, their lives no better than the livestock we all keep.