I bought eight BO pullets back in the spring and now have only two left. They all grew to be beautiful hens and started laying, then one at a time they get lathargic dont eat and their comb goes from bright red to dull, no sneezing or any other signs. The weird part is no other chickens but these have died or even been sick. I have never had problems with hens dieing in the past and this has me absolutely puzzled.....and sick!! what could be doing this?