I have a batch of 5 chicks that I got from the local feed store. Not my favorite way of adding birds to my flock, but I needed some layers and after one incubator fail this season I just wanted to be sure to have a few more hens this year. So this chick was looking perfectly healthy until yesterday. I noticed when she was eating food she was crouched down on her "heels," with the tarsus horizontal to the ground. I was suspicious, but hoping that she was just really into her food. Today she is walking only a little, and when she does she has a very awkward high-stepping gait, and seems like she's going to tip over. Then she plops back down. She is only about 4 weeks old, and labeled at the store as a "Whiting's Welsummer hybrid." I'm sure breed has nothing to do with it, but just thought I'd give the info. Is it possible for Mareck's to set in at this age? If this is what she indeed has, does that mean my other chicks have been exposed, and possibly my adult hens (separated) as well? Should I immediately cull her to hopefully stop anything from spreading?