cocci is everywhere in the soil. Are your chicks on the ground or have you just put them on the ground. Some will succum to cocci just because of their immune system can't fight it. My chicks started out on the ground so I started them on medicated and electrolits due to travel stress. Any stress in my eyes gets some electrolites just like people. (also there MUST be something in the water, I just had to put down a 40 year old horse and one dog is 14, the other is 15 + deaf + blind, well catoracts, so she can see to the side. She finds you with her nose. She eats, drinks and wags her little stub.
I ordered 30 chicks understanding that some would die in shipping and ect.... WELL not at this farm. Unless something comes out of the wood work I have 31, 10 week chicks that are CRAZY. (Ideal through in one extra) Now I have some for sale! My hubby said something scared them and all 31 went through the pop door in 2 seconds!
They are vaccinated for Mereks.
What about lice and or mites. Also can be made worse from stress of maybe a little cocci? Leg mites? Vasseline on the legs and Seven dust the coop. Check around the vent and under the wings. Can make them animic and weak. I use DE earth and 7 in the coop and where they dust bath.
And then it maybe just be failure to thrive.
Bugs and a little cocci would be my bet though. Bugs can come from wild birds, another thing that is everywhere.