Chickens with bare backs

[egrey]

Hi I have about 40 chickens and they have no feathers on their back anymore, The backs are red now, Can somone help me and tell me what this is. there is no rooster in with them Thanks

 

[La Mike]

Check them for mites or plucking

 

[Irishgirlkgh]

I have 5 barred rock hens. I've never had a rooster, and 4 of the 5 have bare saddle areas. I think it's plucking, but don't know how to prevent this from happening. I've upped their protein intake, used the purple dye spray, etc., and nothing has helped. Any other suggestions?