What I've tried over the years.
Extra cheap canned fish. About 1/2 an ounce per chicken every day or two or three days. Because, yes, it's true that animal protein makes feathers grow more quickly, although they can't grow more quickly than the chicken is programmed genetically/hormonally to grow.
Extra sunflower seeds. Black oil sunflower seeds. I give what fits inside of one of my hands for every three hens. I had one chicken once that had to grow three sets of back feathers one fall due to being pecked by another chicken(s). I gave her her very own handful every day. Worked like a charm. Of course, too many sunflower seeds is a no-no because they grow too much fat (I hear). But they also are high in protein.
I feed whole oats with the hulls on. Sometimes feather picking can show a lack of roughage in the diet. Not always. It just depends. At least that's what the poultry folks at some universities say. Free ranging is supposed to help, too.
They say overcrowding can be an issue. But that's not always the issue. I think they just get in a bad habit sometimes.
That's all I can remember.
I also don't know much about bare bottoms. For whatever reason, mine don't end up doing that. Part of it is because the roosts are far apart ... you know, the lower roosts are far from the upper roosts because I was afraid of bare bottoms. However, some chickens (not mine) still peck bottoms even when they're both sitting on the same roost. So I don't know.
Some say that the bottom pecking is because of mites. If mine are getting to dustbathe whenever they want, then they don't have mite problems. If mine have a mite problem, it's because I'm having to keep them in a coop/run config and haven't put the bathing container in. Usually they free range and bathe whenever. Oh, and I sprinkle that food grade DE stuff in the nest boxes and coop. Yours probably don't have mites. But the mites are itchy and bitey and so the chickens peck at themselves.
Will these ideas work for every chicken every time? Nope. Try this. Try that. Go with your gut. Make wishes. Cross fingers. In the end, sooner or later, they will grow their feathers back. That's what they do. Unless those feathers are broken off in the follicle and then sometimes they don't molt out of the follicle and then never grow back. I have had a rooster with a tail (the long feathers) like that (broken off) for about three years now. But he's still doing really well and is one of my best buddies ... or at least he thinks he is.
