just because they were vaccinated for coccidosis it does not mean they can't get it. there are different types of the vaccine and none of the types cover ALL 9 strains of cocci. you can look this up if you doubt me. so if the chicks came into contact with a particular strain that wasn't covered by the vaccine they can and will get coccidosis. keep in mind you do NOT have to have bloody stool to have coccidosis. in my opinion that's likely what the chicks have. I would stop the other medications and medicated feed and treat with corid. corid does kill ALL 9strains of the cocci while other medications only kill SOME strains. you can get Corid at the feed store in a liquid or a powder form.. I really hope this helps. best wishes.
First, there is no proof that these chicks were vaccinated for anything. This is only an assumption made and right now is just muddying the waters. Most places that sell vaccinated chicks here in the US will disclose that information right up front with a sign or at time of purchase. Places like
Tractor Supply have never offered vaccinated chicks except through special orders. Buyer beware, never assume anything when purchasing chicks.
Corid is the drug of choice when cocci is first suspected as it does kill all 9 strains of Coccidia in it's early stages. Yes there are strains of cocci that will show resistance to the amprolium in the Corid but those are usually a strain that have mutated. You find this regionally and on a coop to coop basis. The way amprolium kills the coccidia is by starving it of the thiamine it needs to grow and reproduce. With a resistant strain, these little buggers have learned how to bypass the lack of thiamine and survive anyways. This is when you reach for the Di-Methox, or even in some hardcore cases, the Sulmet. Something else to think about, some coccidia like different parts of the intestine. When you get the cocci down into the lower parts of the intestine, it's darned near impossible to treat with the Corid.
Another issue with coccidiosis, if you do not catch it fairly early in it's cycle, your birds can become damaged inside. Now you're getting into an enteritis. Still treatable but has lasting affects. Birds with damage intestines will always have some kind of coccidiosis symptom ever after. Do they still have it? No but since there is damage to their insides they will appear to. Failure to thrive, as well as other flock mates, smaller eggs and sometimes no eggs if the damage is extensive enough. They are also very susceptible to any virus or disease that may come their way, remember, immunities start in the gut, if it's damaged, it can't work properly in any fashion.
While Corid is fairly innocuous and probably wouldn't do any harm, more information is needed here to be sure something else isn't going on. Under the Stickys on this forum, there is a list of questions that should be asked and answered both by the person posting and the person answering. If the information is given, then the rest of us can start breaking it down by our experiences and knowledge. That's the best things about BYC, the collective information, usually gleaned the hard way from each experience we have faced.
