My 11 month old Australorp just started having difficulty climbing the ramp to the coop. She has to start at the base and after taking a few steps, falls off the side to the ground. She no longer roots with the others either and has started sleeping in a nesting box. She seems to be having difficulty jumping as well. She seems to be eating ok and is pooping. She is molting as well and has a large spot of feathers missing on her chest. She does not appear broody because she will defecate in the nesting box at night and spends the day in the run. She was vaccinated for Mareks. Anyone have some insight?