Feather loss can come from molting or feather picking.
Have you seen your chickens pecking out each other's feathers? Or are they self picking? In either case, sometimes feather picking is as a result of a dietary deficiency. You can try adding protein to their diet to see if this helps. Feather picking also sometimes is caused by overcrowding and/or boredom. How many chickens do you have in how big an area?