My hen started limping while I was gone over the weekend and my husband was watching her. I came home and on Sunday noticed she was limping, I looked her over and cant see any signs of injury. She was bought at a hatchery and vaccinated for Mareks. Can a hen still get it if they are vaccinated. I have 7 hens, she is about 6 mths old. Thy have a small coop with three nesting boxes but a whole large corner of our yard to range in all day. Thanks for any advice.