One of my barred rock hens who is about 2.5 years old lost her feathers on her back and head during a molt about 1.5 years ago! She never regrew them! Other than looking awful, she has been a happy hen, laying about 3-4 eggs a week for all that time. Now she is losing more feathers around her neck and has been dropping her eggs from the perch at night. Every once and a while she will lay an egg in the nesting box, some are soft shelled, one had no shell, just a perfect yolk laying atop the other eggs in there.
I have dusted her for parasites, although I haven't seen any on her and the other three hens that she lives with are all ok. I once asked a vet why she never grew back her feathers after her first molt and she thought it had to do with hormones. Now she is losing more feathers. Is she molting again? Is she just getting old and not laying so well anymore? Not sure if there is anything I should be doing for her.