I found one of my ameraucana hens on the floor of the coop unable to stand up or even hold her self up right. She was still eating and drinking last night but now today she's gasping like she can't breath. She can move her legs but she's very weak. She's a little on the thin side. I can feel her breast bone. I dont have any other chickens showing these symptoms. No it's not mareks. This one has been vaccinated.