My 13 week old chickens have started dying off! I make sure they have plenty of food and water everyday. They don't seem to act like they are sick or diseased. I found one today that was dying....it was laying on the ground and it would throw it's head all the way back and act like it was gasping for air and twist it's head like it was in pain. Might anyone be able to tell me what this may be, or has anyone seen or heard of this before?