Usually keeping them a dustbath will keep the lice and mites away. You can add DE to the dust bath and will help in preventing them but if you do get them treat with Seven dust. DE will not work on an infestation. Check periodically around tail and vent area and rub your hand across the roosts. If it turns red you probably have mites.
Thank you for this post/question! I was wondering the same thing. I see our chickens taking their usual dirt bath, but wondered if I need to add some 7 Dust in their bathing area to ensure that we prevent mites and lice.