I have twice had an Indian Runner go off it's legs and I blamed the Aylesbury drake who was so much heavier, after seperating her and letting her rest up she recovered after a couple of weeks, needless to say the Aylesbury drake had to go. I caught him up with the intention of dispatching him and having him for dinner,but he was so soft I just could not do it. He is now happily rehomed with Aylesbury ladies of his own. I have also had 2 with infected feet which required antibiotics, but they do seem to recover well.