I breed for resistance also and do not implement any biosecurity measures other than getting new chickens as day old chicks from a hatchery, if needed. Usually I just hatch my own. If I'm interested in introducing new breeds into the flock, I just buy the chicks.
I don't prevent anyone from viewing my chickens and I don't worry about wild birds, mice, or other vectors. If my birds have an adequate immune system, they thrive. If not, they are culled. So far I've not had any with poor immune systems, nor had any illnesses in my flocks over all these years.
I don't vaccine, feed medicated feeds, nor use any meds of any kind.
I don't prevent anyone from viewing my chickens and I don't worry about wild birds, mice, or other vectors. If my birds have an adequate immune system, they thrive. If not, they are culled. So far I've not had any with poor immune systems, nor had any illnesses in my flocks over all these years.
I don't vaccine, feed medicated feeds, nor use any meds of any kind.