Every few poops chickens do what's called a cecal poop. They usually are runny, dark brown, and very stinky, and very NORMAL. Are you sure it's not the normal runny brown cecal poop your seeing? If all poops are runny then yes probotics will be a help, in fact they are good all the time for growing chicks. I prefer probios probotic. Hope this helps.
Edited by realsis - 4/8/16 at 2:24pm