My chicks have all been doing fine so far, but one of my cornish rocks has suddenly become sick. I noticed yesterday that he stayed apart from the rest of the flock, didn't eat or move around when they went outside, and didn't seem to care when the rest of them moved pretty far away from him (usually they panic and scramble to catch up with the others). Today it's worse - every time I look at him he's standing there with his eyes closed and not moving. If I nudge him, he'll take two steps and then stop and close his eyes again. He opens his mouth to peep sometimes and just a raspy breath-y noise comes out, no audible peeping. Can anyone please tell me what's wrong with him, and what I should do? Do I need to cull him before it spreads to the other chicks (who all seem perfectly healthy), or can he be cured? Please help!