Hi! I have 10 hens, 8 are a year old, varying breeds, and 2 are about 3, yrs/4 yrs old. A few weeks ago I noticed almost all of my ladies had bare bottoms, from the vent area down to their under belly. I started spraying them with a natural remedy for mites/lice. Nothing seemed to help, I started dusting the roost each night with DE. Still nothing, Now all of them have bare bottoms, and two now have what looks to be broken off, or chewed off back feathers, and tail feather. Egg production is not bad, but quality of shell has been affected. I guessed it to be because they are trying to regrow feathers, so all calcium is going for that. Fed cat food a couple days and have been upping their calcium and protein intake. Last weekend I treated the coop, without actually cleaning it, due to time I had available, with Permethrin. But over this last week I now see 2 other hens having the same broken/chewed off feathers on their backs. I plan to treat the hens again with a stronger force this time, and use Ivermectin for cattle, in the correct dosage for poultry of course. I also will retreat the coop again. I am at a loss as to what is doing this to my hens? Am I not doing something I should be to help them. I bathed the two worse hens last weekend in flea and tick shampoo to help also. Sad part is, nothing is helping, and I am fighting an invisible invader! My hens are on Nutrena crumble, and fresh water with garlic and ACV in it daily. Treats are limited. I took pictures of the two worse ones, and can upload to show you the broken/chewed off feathers if that would help? Can anyone help me?? Please Thanks in advance!