Is there a Purina product that helps with the prevention and/or treatment of mites.
What are the precautions when using mite powder in proximity with chicken feed?
As far as I know there isn't a one particular feed designed to prevent or treat mites, though the best bet would be to view it from a complete nutrition standpoint. Even if there was a feed designed for this purpose it's important to remember not to always use the same thing for an extended period of time as mites can become resistant to the different methods of control if used too often, which is why you should alternate between 3-4 different products.
One should always use dust or treatments away from feeding areas, so if dusting, pull birds out then dust then put them back in. Same for storing pest treatments and feed; different containers and different locations for each, i.e. don't store pest treatments and feed in the same shelving area, but can be stored in the same room. Hopefully that makes sense.
There isn't a Purina product specifically designed to prevent or treat mites. Mites are external parasite, so the best way to keep them in check is providing a dust bath for your chickens. In that dust bath, mix equal parts peat moss, sand, and wood ash. You can add a smaller portion of diatomaceous earth (food grade only) to that bath to aid in mite control. Practicing good sanitation will aid tremendously in preventing an outbreak of mites. If you do have an outbreak, be sure that you are using a miticide that is approved for use in poultry. You should consult a veterinarian for more details if this does occur.