One week ago my 3 year old BO hen began displaying some lameness issues- laying down more, not wanting to climb back into the coop at night. She still had a good appetite, and has continued to free range and forage with the rest of the hens. She has also continued to lay normally. Today I noticed that my also 3 year old EE hen was laying around more, and quite stiff when she rises. She too is foraging and eating her crumble normally, but just doesn't look right. Both these hens are acting as though they are laying on their hocks, in a more reclined positon than if they were simply laying in the sand or sun. I have them housed in a large coop with 4 other hens- all are the same age and all were vaccinated for Mareks when I bought them as day old chicks. I de-worm, clean and change bedding regularly. Can they still get Mareks if vaccinated? What could this be? Do I need to worry about the rest of my chickens? I appreciate any advice you can lend! Thank you in advance.