All four legs and most/all of the flock?
I am afraid I cant offer any advise but would also be interested.
We have a few that have lost fleece on the back end and legs due to various things that happen round the back end but never seen a retraction on the front legs or anything that cant be attributed to the other obvious aliments they suffer from.
No clue but if they are eating well and are fit they are in a good position at the moment.
Baz