I think you will find that the mycoplasma is pretty much everywhere, and most all chickens have been exposed to it at some point. Anyway, the point I was trying to make is that you can keep chickens that can't cope with CRD, even if they continue to show symptoms without affecting your flock as they all get to cope with it either way. What I do recommend though, is not to breed fowl that can't get over CRD on their own. This just weakens your whole flock. I am not against medicating, and keeping birds if that is your desire, but on my yard, if they can't cope with any kind of respiratory disease without meds, they get culled. This way I promote a more hearty flock, that will be more disease resistant down the road. But, to some people, it is better to medicate and keep them as they are more of a pet. You have to make that choice yourself. BTW, Baytril is some good stuff, but you need a script to get it. Tylan is just as good, and you can get it OTC. Good luck!