I do have to mention this though. We have had chickens for 16 years and normally never have a problem with cocci, we've had lots and lots of chicks. But this year is different. We've had lots of torrential rain, followed by extreme heat, followed by lots more rain, then heat, etc. This is ideal conditions for Cocci to thrive. I have lost two chicks and one pullet this summer due to cocci. The last pullet I lost yesterday. She was 9 weeks old. She had Coccidiosis at around 5 weeks, I caught it, treated it, and she recovered. Her hatchmate did not get sick, but I treated her anyway. I did not give vitamins afterwards, but this past week I gave the entire flock vitamins for a week. It's hot, they're molting, I have broodies, there's lots of chaos out there, and I like to give vitamins for a week at a time in conditions like that. Well, we surmised that that is what killed our pullet. I didn't notice that she was sick, she seemed fine...but they do free range so I didn't have her under close observation all the time. Anyway, we think she had a cocci infestation, and the vitamins for a week just caused them (the cocci) to breed like crazy. She got sick the night before last and despite my efforts to save her by force feeding her Corid, she died yesterday afternoon. I mean she went down extremely fast. So point being, you really need to watch it, because reinfestations are common in weather conditions like I described. I don't know what the answer is. I am just sick about losing my pullet. She was so beautiful and her remaining hatchmate has no friends now and is so lonely.


But THAT pullet seems healthy and of good weight. It is just too weird. And I don't know what the answer is besides just being vigilant.
Normally adult chickens don't get coccidiosis, because they develop immunity. But this year I had a five year old JG hen get it. I treated her, but she also developed a gut infection because of it, and I had to treat her for that, too. She did recover after a couple of weeks. They actually develop immunity, and keep it, by consuming their own poop. Which they will do naturally, like it or not, because they eat off the ground.
Lastly, they CAN develop a gut infection from either worms or cocci, and that's when you need antibiotics. But again, you just have to watch. If you have one that doesn't recover from treatment for internal parasites, that's the next step.