Hi, I am new to owning chickens. I have five bantams, all hens, a variety of types, all different ages. My oldest (don't know what kind she is) supposedly just old enough to start laying, which she has been doing until it got hot, was found last night in a corner of her yard unable to stand. She eats and drinks, poo is absolutely normal (not runny, not smelly, no obvious worms). She is unable to stand and is very thin. All five eat like champs. The next oldest, a red silkie, who has not started laying yet is also thin but still very active. The remaining three are game hens, new chicks this spring and are fat. Any ideas as to the problem?