My chickens free range too. They had medicated starter when they were little chicks, but no other meds since. I've never had a problem with diseases or parasites. Just keeping their bedding and water clean, and good flock management seems to do the trick. I don't use DE or ACV, but I'm sure it wouldn't hurt. My flock is now 25 weeks old, and doing great! This is the first time I've raised chickens, and it's been really easy and rewarding.