I walked over to the brooder an peeked in and one of my chicks was laying dead on the ground. I have no idea what happened. They were fine and all acting normal two hours ago when I checked on them. I checked her over and she did not have pasty butt, or any signs of infection such as nasal discharge or a cough. It's not even my "runt" that I was worried about umbilical infection. What could it have been? Do I have to worry about the others dropping over dead? I'm so upset!