I have a hen that has been very active until a couple of days agoand walks slowly with her tail slanted downwards, mind you I have never seen her lay an egg since I've had her,although she enjoyed sitting on other hens eggs and empty nests,but not for long. Anyway, for the last couple of days she has seemed to walk slowly,like an elderly woman. She still eats and my other chickens don't seem any different towards her at all. Does old age set on suddenly with chickens? She doesn't seem in any pain.