It is a bit of minefield isn't it. I seem to remember when we had a highland heifer who broke her leg, the rules (which I would have to admit we looked at after, as on welfare grounds she needed to be dealt with asap) said that myself or my husband could shoot her, as her owners, as it was for her welfare, but our friend, who is a slaughterman/butcher could not, unless he took her to his premises. That seemed madness. It was a few years ago now, so maybe (hopefully) things have changed. She was very tasty.
Re the Autumn castration of lambs, I presume to be legal this would have to be done surgically by a vet?