Coccidia is in the chicks' feces. It is also in the ground, but only as the result of contamination by feces. Healthy chicks pass the organism harmlessly in their stools. Complications occur when coccidia build up in the environment and then get ingested by the chicks in numbers that eventually overwhelm their system resulting in a serious infection. The way to avoid it is to keep the brooder clean, especially the feed and water. If the feed and water are kept free of poop and the brooder kept fairly clean (change the litter when it gets too poopy), then the chicks will ingest a small amount of the cocci by scratching and pecking in the litter. This is a good thing and will help the chicks develop immunity slowly. If the brooder, and especially the water and feed, is allowed to be overly poopy, they will ingest too much too quickly and overwhelm their immune system and become sick and many will die if not promptly treated--the key word being promptly. Once it strikes, it moves quickly, especially the younger the chicks are.
Medicated feed will help prevent it, but I prefer to keep things clean and let them build natural immunity.
Coccidiosis is most common between 4 and 14 weeks. After about 14 weeks, if raised on the ground, they will have built up sufficient immunity to substantially reduce the risk of infection.
UGCM