Last spring I lost a Delaware to what appeared to be Merricks, she was a year old. In December I lost my Buff without much warning, she was being a little quiet and I noticed she was thin and not sitting on the perch with the other chickens anymore. I had gotten her at the same time as the Delaware, but from a different source. At the same time another chicken, approx 6 months old, suddenly couldn't walk on her right leg. She seemed ok other wise, she held on for almost 3 weeks then passed. Now, her "sister" (same breed purchased at same time) is being very quiet and is not sitting on the perch anymore, but seems to be walking OK. She also seems thin. (food and water is available at all times). I am going to remove her from the remaining 3 chickens tonight into a dog crate to separate her. What could be going on???? They get layer pellets, scratch, and some crushed oyster shells. I give them warm water twice a day (it is very cold here).