I am fairly new to the chicken world, having moved to a place with a flock of 20-some chickens 6 months ago. This flock consists of birds of a variety of breeds and ages. They sleep inside a house at night and have free access to a large run (possibly an acre). About 1.5 - 2 months ago (approx when the chickens began molting) a rooster started looking very depressed. He got this hunched-up look, like his neck suddenly disappeared or shortened, and his comb got very floppy. He became progressively lethargic, moving around slowly, and he eventually developed a loud rattling noise. He died after 2-3 weeks of onset of symptoms. Then the same thing happened to another rooster, which died a couple of weeks ago, and a hen developed the same symptoms. This morning, I found that hen dead and noticed that another hen was hunched up and lethargic. This seems to be happening in the older birds in the flock, but I'm worried about the rest and wonder 1) what the heck is going on?! 2) what I might be able to do for the sick ones, and 3) protect the rest of the flock. Of note, almost 3 months ago, we bought 7 young birds from a local breeder: 4 chicks aged 3-5 weeks old, 2 pullets, and a young roo. These birds were "isolated" in old rabbit cages inside the chicken yard. The older ones were integrated after a few weeks and the younger ones a few weeks after that. There had been health issues in the chicks. One died 2 days after we got it. It quickly developed balance problems and then stopped moving. Two others had eye issues. After terramycin treatment, one chick had a complete recovery and the other one had a partial recovery (one eye normal and one that is cloudy and bulges somewhat from the socket). I don't know what exactly these problems were about either. Anyway, the onset of problems in the older flock does seem to coincide with the arrival of the new birds, who were admittedly not adequately quarantined prior to integration. However, I still don't know what exactly is currently going on in my flock or what to do about it, if there's anything that can be done. I'd appreciate any help the BYC community can provide.