I am not sure what is wrong with my hen. She is a Red Star Hen about 11 months old. She is the only one acting like this. She humps up her back and shakes her head. She started doing this last week one day. The next day she was fine, then started again about three days later. Then she has been a week free of this. This morning when I went down to feed she was in the hen house and the other chickens were outside. She would not even get up. I picked her up and she cannot walk. She is doing the same thing with her head again. What could this possibly be?
I first thought this was some form of neurological disorder, but it turns out the hen was egg bound when this happened. She was laying very large eggs and having trouble passing them. If your hen regularly lays large eggs and starts acting like this she may be egg bound.
If you suspect she is egg bound, check for the presence of a stuck egg. Dip your finger in mineral oil (NOT mineral spirits) or Vaseline or other petroleum jelly and insert it as far as you can into her vent (cloaca). If you can feel an egg, lubricate her vent well (and the end of the egg that you can reach) with the petroleum jelly or mineral oil to help her pass the egg. You can also gently push up into her abdomen with your other hand to try to work the egg toward the vent. In the worst case, you might have to break the egg inside her if you can reach it, and remove the pieces of shell, but that may cause damage to her vent/cloaca so should only be a done as a last resort. If you have to do this rinse her vent area with hydrogen peroxide afterwards to prevent infection.
Gail Damerow's "Chicken Health Handbook" suggests egg-binding may be caused by a deficiency of Calcium or Phosphourus.