I battled a round of cocci this spring in my outdoor grow out pens. Amprolium (Corrid) did nothing for it so had to use Sulfadimethoxine. I lost 2 chicks that were over 5 weeks old. Because I must have a bad kind here, I've started giving my chicks one round of Amprolium at 4 weeks before they go outside and 20 days later a round of the S drug. I may alternate them another time or two especially if I have any new cases.On the California Northern thread we call it the S (Sulfadimethoxine) medicine. Out in the Sonoma County area, some have to use it because the Cocci is very bad there and chicks die without it. Here in Woodland, Corid works fine. It would be a good medicine to have on hand if you had a type of cocci that was killing your chicks. Some Breeds seem to have less resistance to cocci too.