I have found that even in the brooder, if they can have a little sand, it seems to help with the pasty butt. I'm going to try that quinoa too next time I have a problem. My latest batch are all nice and clean, no problems so far.
The Quinoa has a full grain, so has the roughage needed (fiber) and hydration qualities, so no pasty butt here !
I also use "Broiler Max", as it has FULL vitamins & minerals, and rooster booster does not.
Broiler MaX at 1/2 dosage for all my Buckeyes.
Awesome stuff for growing large framed fowl.