Acclimmating birds is not bad idea but birds will be picking up cocci and bringing them back to brooder. In brooder cocci can be a real killer since chicks more likely to consume tainted feces increasing the infection rate beyond what their immune systems tolerate. Infections can be aggressive enough that usual treatments are not effective. When I write usuall, I mean inorganic (coccidiostats) and organic (probiotics). Wet conditions outdoors excacerbates this. I have lots of experince with hand raised to back this up. Some dominique strains are more resistant but that is within limits.