To piggyback on Buff's comment about apple seed toxicity... They contain small quantities of cyanide. It is important for parents to know this. Small children can often become fixated on certain foods (like apples) and want to eat them everyday. The ocassionally apple seed isn't going to hurt anyone, but if someone regularly ingests them, it could cause problems. Since chickens are so much smaller than humans, I would guess that it would take fewer seeds to affect them. If I were feeding alot of apples to chickens, I would probably core them first.