All their feathers on their back 1/3, also under tail and butt area? I'm sure it's from the rooster. There is one rooster with 20 hens. Only 6 or the 20 are like this, then because it's bright pink the other hens peck on them. I have used the blue antesptic spray but in 2 days it's all gone and same thing, I can't afford to buy a can a week or able to catch the chickens everyday and spray them. The are in a fairly large run (not free range) it's about 20x30'. I've heard there are things you can put on the hens to protect them but have no idea how that would work?