Regarding mites and lice: I raised my poultry on raw garlic as part of their staple feed, and was always able to bring in a bird from outside with terrible scaly leg mite infestation or lice, and treat it through diet, no dusting or extra feeds or special feeds, just letting their bodies build up on natural defenses. I never had to treat perches or other birds or nests. Once or twice I backed off the garlic to see how much of an impact it had, and immediately parasite levels rose, so I amped the garlic back up, problem solved.
In the case of severe scaly leg infestation, like when the bird's lost most of its scales or is in obvious pain or is even going to lose some toes, I use pine tar (stockholm tar); it's a great pain and infection killer as well as insecticide. The scaly mite infected areas just shed off and leave fresh healed skin and scales in their wake after about two or so applications. Animals love it; I use it on the sheep's hooves, on fox bites, gangrenous or golden staph infections, messy accidental amputations, all wounds, cycsts, and generally anything. Some people think scaly leg is normal; I read one commercial layer book saying it was an indication of age! Great herbs to regularly give your poultry and other animals include sage and rosemary, and all aromatic herbs are generally useful as medicines. I've heard really great things about oregano oil, it's one of those up-and-comers in the medical world because recent studies have proven great efficacy in its applications. Wish I knew where I'd read that! I will link if I find it.