I tossed a clump of sod from the yard into the brooder when the chicks were 2 days old, while I was still brooding them in the house. Now I do all of my brooding outdoors in the run from the get-go, right on the same floor and litter that all of my chickens and older chicks have been on. I rake out the top portion of the litter, put a little clean down on top of what remains, and let 'em go. Don't know what good that clean, fresh upper layer does - they have it all scratched down and mixed up in a few hours anyway. But that's what Mom would do, and it's working very well for me.
That is definitely advisable. I also do that with brooder raised chicks or broody raised ones who can't get outside within the first week of their lives due to weather. Broody-raised chicks are not as prone to cocci as brooder-raised ones that don't get out on soil early. Still, if you have a particularly bad wet prolonged period, cocci can still rear its ugly head. Best to always just have Corid on hand or know where you can buy it in a pinch.