Corid does not treat all types of coccidia. Were they on a preventative dose or were you treating them as if they had coccidia? It is possible that you are dealing with a strand of coccidia that is or has become resistant to Corid. I would switch to sulfadimethoxine.
Have you had their poop...
Sulfadimethoxine is Albon. We were told by our Poultry vet that it is the safest of the Sulfa type drugs for chickens. The other drugs have side effects.
Our rural king in kendalville is disgusting. And full of lazy people. I hate more than anything to see chicks with pasty butt. Out of all their chicks I would say a good 65% had quite a bit of buildup. I asked if anyone was in charge of taking care of the chicks. NO ONE knew what the heck was...
A lot of people think that tilling with a tiller is a great thing. Yes it makes the soil nice and pretty and easier to plant in, but it also brings up weed seeds. The best way I have found to keep weeds out and have awesome soil is to mulch. I get the tree company to drop off a few loads right...