It is likely as others have said that there is some feather pecking going on in your flock. I would also agree with the vet about having patients. Unless the feather damage is severe, the feathers only grow once a year. All feathers lost since last late fall have likely not grown back. We are approaching that time of year (in us), but a few months away from all hens over a year having a full molt and regrowth of feathers. In about 2 months your birds will look different. Continue looking into stopping the pecking before pin feathers appear, so they are not plucked the new feathers before having a chance to grow.
