I have a three 13 week old Barred Rocks. One has become very lethargic. Her crop is squishy and seems to be filled with gas. They are with older chickens most of the day and I was wondering if her eating layer feed instead of chick feed is causing a problem. They are all over the backyard. She has been like this for 3 days. Very concerned. Any ideas would be greatly appreciated. THANKS!