This is my concern as well. It seems that every time I bring new pullets into my flock, they start having bloody poop within a week. I always treat with corid as soon as I see the blood, and believe me, I really look for it so I can treat as soon as possible. Some don't show any sign of weakness with the bloody poop and others get very weak and die. I believe that in the more severe cases they have more damage to the intestinal lining which inhibits nutrition absorption, making them weaker. That's why I was wondering if there is a preventative dosage that I could give, so that they might get introduced to the cocci without it doing so much damage. From what I've read, it seems that all poultry get this disease. The trick is to control it by introducing it to the new bird slowly to allow them to build immunity. I usually get my pullets at 8 to 12 weeks of age, keep my coops and run very clean, and there is plenty of room in the run and coop. I'm not sure why I have such a problem with this, but I'm open to any suggestions. Thanks!