Welsummer hen? She is seven months old and not laying. About a week ago I noticed her periodically shaking herself, more like a shudder or shiver, like she was cold. I didn't think too much about it at the time. But on the weekend, she started to sort of stumble like her motor skills to her legs aren't working quite right. Sometimes she is down on her hocks more so on the left side instead of totalling standing. She is eating, drinking and pooing OK. But she does seem underweight comparing to her hatch mates. She is a hatchery bird and was supposed to be vaccined for Marek's. I isolated her on the weekend, have put "quick chick" powder in her water. She is eating layer mash and scrambled eggs. I also gave her three drops daily of poly-vi-sol baby vitamins. So far she doesn't seem to be getting worse, but also no better. Anybody have any ideas? I've had chickens for 5 years and never had anything like this.