once a chicken starts this it's hard to stop them . You can buy blinkers for chickens kinda like ones used on race horses (google poultry supplies) and i think they make stuff that you put on the spot and it's supposed to stop it .
The problem starts with sub-class chicken feeds of today ...... people want it cheaper and they got it !!!! the craze for no animal , no fish , Proteins and Fats leads to this 99 times out of 100 . Even some that might include it uses other byproducts floor sweepings roughage by products making it almost worthless ....... we are lucky that chickens are so tough to be able to live a couple years on what they call feed .... they will tell you to replace your layers every 1 up to 1 1/2 half years of age (so what does that tell you ??)