Broken feathers. What is going on?

[MadelineT]

I came here hoping to find some answers for why 4 of my 6 girls have these broken feathers on their rumps like the picture. All three Wyandottes have these fuzzy looks with snapped off feathers and my little Polish looks a wreck missing feathers on the back of her neck and under her chin.
I feed them an organic, soy-free mash with 16% protein and they get lots of fresh veggies, broccoli, cabbage, collards, mealworms and they live in a large tack shed and a large enclosed outdoor run.
I have checked for bugs and don't see anything.
The feathers actually look like a *V* on the end, like they are snapped off? And underneath is this fluffy grey *fur*. I'm out there often with them and don't see them over-picking at each other? They are just one year old. They sleep 5 feet off the ground with a reptile bulb....do you think the heat is doing it? I don't think it's mice as I've read elsewhere.
I'm at wits end! They look a MESS! I'm still getting 4-6 eggs a DAY so I don't think it's molting???

I know it’s been several years.... but did you ever figure this out? I have the same issue and can’t find information ANYWHERE. I feed high protein, etc etc etc and they look totally wrecked.

 

[SBaltz]

Straw mites or itch mite get into shaft and it breaks.
treat with lice shampoo or shampoo with Neem oil. Leave on for 5-10 keeping it lathered adding extra shampoo and water. Do this 3 times in one week.
these things are microscopic. Can’t see with magnifying glass. Use a microscope on a broken feather. They can get reinfected with straw. DE all straw or bake for 1 hour at low temp. Above 165

If you can’t see the straw mites/itch mites without a microscope, how can you tell if that is the culprit? I am having several girls with picked necks and backs and I can’t find evidence of mites.