many thanks for that link @L-plate chicken mum ; I hadn't seen it, and I will settle down to read it carefully tomorrow.Have you seen this thread? https://www.backyardchickens.com/threads/lame-chicken-not-mareks-a-rare-account-of-recovery.1290351/ Might be something useful there?
And yes, Aberglasny has stunning plumage.
Fingers crossed for Cadoc