I've kept a small flock of chickens for the past three or four years. I always buy a few feed store chicks at the beginning of the season and have never had a problem. This year I bought feed store chicks plus brought a few home from friends. This year - problem. Yesterday my 17 week old silkie roo (from the feed store) was acting completely normal early in the day. In the evening when it was time to come in to the coop I found him way out under the trees where they normally dust bathe. I approached him and he didn't run. A few flies had actually started pestering him. The lil guy couldn't walk much less stand. I found no sign of injury. I brought him in and held chick starter up to his beak. He ate quite a bit. Today he's tried to stand but can't catch his balance. Both legs do move, though, and feet are forward. He was medicated feed for the first month or so and has since been on all flock as I have ducks, rooster, pullets, and hens all eating together. My first thought was mareks and I'm very nervous as I have unvaccinated sebrights, silkies, and also LF chicks that just hatched a couple of weeks ago. Also, his poo does look normal. It's actually kind of like broody poo since he's in that crate in my basement. Any thoughts?