My chicks are now 7 weeks old, and I found this out in the pen this morning. I've been keeping them in the old chicken run until they're big enough to be integrated into the permanent flock, so I knew they'd be exposed to cocci spores, but I fed them a cup to half a cup of medicated feed a day mixed with their regular food to help them build an immunity. I only took them completely off the medicated two or three days ago. So me and my poor judgment said that they had received enough immunity by now....I'm ready to kick myself I should treat this with Sulmet, right? Should I go ahead and treat all of them, as a preventative? Also, should I put them back on the medicated feed after I finish with the Sulmet? Thank you for responding, I thought I was doing everything right with raising these chicks...until now.