Help! 7 of 9 chickens all have feather loss & red bottoms

[Lavsbeemitchell]

Hi there ! We have a large coop 12x12 with four roosting boxes and a large run 25x12 feet. 7 of 9 chickens started loosing their bottom feathers and now then appear red and painful. They all roost in the same long rung except for the two that has the least amount of feather loss. Some birds have this starting on their backs as well as their legs. What can I do ? We have treated with DE. Is there perch too rough? Do they need more protein ? how much apple cider vinegar do I put in the water ? How much ginger powder and where ?
thanks in advance ! They are all laying 1 egg per day

 

[MysteryChicken]

I suspect feather eating, & bullying.

 

[MysteryChicken]

What's the protein content in your feed?