One of my 2 week old BO chicks was dead in the brooder this am. Nothing appeared to be wrong with it. I'd lost a few others after I first got them but after taking out the wood chips and giving Poly-vi-sol in water for a few days everyone has been very happy, alert, etc. with no pasty butts or anything else wrong. Last night I gave them a lettuce leaf to play with, its the first time for treats. Do you think that may have caused the chickie's death?