I have a 5-6ish year old Wyandotte hen. About a week ago she seemed to lose her voice - making quiet wheezy noises instead of usual chirps (but not actually wheezing). Now she's walking very slowly as if her legs are giving out. Doesn't eat but touches her beak to the food as if she can't quite reach it, however close it is. Can't seem to actually peck anything. This morning she fell over once, as if one of her legs had just stopped working, but got up again. She walks as if it's painful, but there doesn't seem to be anything wrong with her legs. Otherwise, her eyes are bright, comb red and feathers shiny. She had leg mites briefly in the past but has always been very healthy with no other problems. I don't know if she was vaccinated against Marek's disease. Could whatever this is be caused by bad food? The shed where the layers' pellets are kept has been dampish recently. Help!