Chicken with tail down, kind of off balance

[StephJShank]

This chicken is not of laying age yet, so no egg bound issues. Today she started tucking her tail and seems a little off balanced. Ideas?

 

[DobieLover]

This chicken is not of laying age yet, so no egg bound issues. Today she started tucking her tail and seems a little off balanced. Ideas?

What are you feeding them? That looks like bird seed in the feeder. They need a complete feed designed for chickens.
Was she vaccinated for Marek's?

 

[StephJShank]

What are you feeding them? That looks like bird seed in the feeder. They need a complete feed designed for chickens.
Was she vaccinated for Marek's?

That was a treat (game bird scratch) to get her to come to the feeder. They're being fed flock raiser.

Yes she has been vaccinated for Mareks, but I understand it can be a leaky vaccine. Is this a Mareks symptom? Still E/D normally, can still run and such, but when she puts her tail down she seems unbalanced. Pupils reacting to light normally.