Hi, I have recently purchased three Silkies. These are my first chickens. They seem to have greasy looking feathers. Does anyone know what would cause this? When I got them, they had lice and mites, so I bathed and dusted them with food grade DE. I can not see anything crawling on them now. Is it normal for their feathers to look greasy? I would appreciate any advice as I am new to chickens. Thanks!