Today I went out to the coop to discover my 2 oldest hens (apprx. 5 and 6 1/2 y/o) were moving a little slow. They are rather old for a chicken, from what I gather, and stopped laying a few months ago. Their appetite isn't as big as it was (they used to eat a lot). Also, their poop seems normal; not runny or green. My other chickens are all acting fine. I added some nutri-drench to their water this morning. Is this behavior out of my two hens normal for old age or is something wrong?