Must admit I had wondered about the exercise bit. Somewhere (can't remember which book) Patrick says something about Buster having been taken out walking, so he's not in bad condition. 'The farm horses', as far as we can see, only ever get used to plough a difficult bit of field, which would surely only happen, at most, twice and probably once a year. And who exercises Idiot Boy and Catkin during the - what? - 40 weeks? that their owners are away?