With my experiences I will only deal with locally bred birds unless and that is a big unless, I am buying them from a hatchery. I have plans this spring to add 6 more Fayoumis to my flock simply because they are resistant to Marek's and many of the other infectious diseases that plague flocks. I have one hen now and she is in with my bantams.
I figure the local birds, especially the chickens that are raised on Amish farms, have developed natural resistance to Marek's disease in our area. My bantam losses are way lower than Standard sized bird losses. 3 out of almost 50 bantams from Amish stock compared to 25 out of 38 birds that came from an out of area breeder. I'm done with Buff O's and Welsummers. I have 13 left. 11 hens and 2 roos. The birds showing signs of decline from Marek's have been culled leaving me with the 13. After loosing 2/3rds of my flock to this horrible disease, I'm done with them. The remaining birds will live out their lives here. They are pampered and spoiled. But they will die from old age or from disease and not be replaced. The bantam crosses I hope will breed with the Egyptian Fayoumi's that I have or will get and give me even stronger, more resistant birds yet.