Food grade DE (codex grade fossil shell flour) is a maintenance plan. If they have lice/mites/worms you need to errdicate it first with a quicker treatment.
i agree with you, Speckledhen. It is always a good thing to practice intensive biosecurity measures with new chickens no matter where they came from. You can bring in not only disease but lice or mites and other parasites that can be fatal to your flock.
Due to several people having horrid...