I have been out of town for a few days, with a friend taking care of my chickens twice each day for me. I have a temporary coop set up in my garage, with 4 hens that are 6 months old, and 2 that are 4 months old. No free ranging, too many predators out here. They have shavings on the floor, and two big roosts with plenty of room for all. They are fed layer crumbles, with a hanging feeder, yogurt, fresh greens, and have plenty of fresh water. There is a cat in my garage, and rodents are not an issue. So, the problem. My friend called me this morning and said one of the younger girls was listless and lethargic. No other symptoms. She had been fine last evening, no problems. I arrived home this afternoon, and she was dead. All the others seem to be healthy, eating and drinking, no signs of worms. As a precaution, I added tetracycline to their water. I don't know what else to do, or what could have caused this. Please help!