Three & a half weeks ago I received my order of 27 chicks. All arrived strong & healthy. They have grown fast & most are feathering out well except for one Barred Rock chick. It is still about the size of a 10 day old chick, & is still all fluff except for some wing feathers. I have them on Purina Start & Grow ( 18 % protein ). Yesterday it started peeping loudly & it looked like it had labored breathing. ( beak closed though ) Today, it is not peeping loudly, but has not ate or drank very much & is sleeping much of the time. No scratching in the shavings like the others, but does have enough spunk to run when I try to catch it to check it out. I decided not to add stress by trying to catch it, instead just tried to look closely when its eyes were shut. No nasal discharge that I can see. No messy butt. Why has this chick failed to develop properly & what do you think could be wrong with it?