I have 25 three week old pullets. Last night I noticed one white rock baby shaking. She looked like she had chills. It is 85 degrees in the brooder so I knew she was warm enough. She is still shaking all over today, but eats, drinks, plays and poops fine. Any ideas? all of the others are acting perfectly normal. They are on medicated chick starter, and get occasional treats like egg, yogurt, grass clippings. Maybe every few days. They also have grit available.