I've always fed my poultry organic. I purchase the grain whole, and grind at home, that way I can control what is in the feed and know that it's not just ground up 'organic grain products' that are on some of the certified organic brands.
It's my own homemade recipe, with all real food ingredients and no synthetic vitamin mix. The hens get eggs shells that have been in the vita-mix, which get mixed into the food about every other day, but depends on how much they are laying. Non GMO nutritional food yeast takes care of the niacin requirements of the muscovies and geese, along with other nutrients for everyone.
The same food is given to the chicks, only ground smaller, added sunflower seeds, and no ground egg shells. No problems with any deficiencies. I try to get the chicks out to forage as soon as possible, but if it's a few weeks they're okay.
It's more expensive to feed this way, but I don't sell the eggs, or meat, and I care about what goes in their bodies, and what goes in mine. It is the true cost of what goes into real food with real nutrition.
Everyone also forages with enough grass and weeds, and they all get the extra garden produce.
If a chicken is healthy enough, and has full use of it's legs, it will be able to get rid of mites by bathing in dirt/sand. Sometimes I may have one that has too many mites, (but has been uncommon recently) and I use Neem seed oil diluted by another oil directly on the bird, and that takes care of it provided the bird follows up by dirt bathing.
All works out well.