Oh, that's quite canonical.
(Lord Peter Wimsey uses it sometimes, ironically, and I think in a rare example of Bunter's POV he refers to "his master", but I may be making that up - it's one of the early novels where Wimsey has a recurrance of his nervous breakdown, and walks in his sleep to Bunter's bed, addressing him as "Sergeant" and worrying about the sappers and the shells. But Sayers is quite clear that Wimsey is being ironical and referencing the Wodehouse novels - as he's aware of the literary parallels of Famous Sleuths, he's aware of the literary Wooster/Jeeves parallel of employer/servant who are also comrades in adventure/friends - and Wooster's admiration/respect for Jeeves, which Wimsey feels for Bunter.)
Also: the bit about the shitting cows made me laugh. I'm wondering if the lawns are fenced-in. All the cows I came across were very curious creatures who followed you around or stared at you while standing in the middle of the road. But maybe the Scottish cattle (E.B.'s cattle to be precise) are really just content with being picturesque. ;)
Diane Duane comments on horses in fantasy novels being better considered a form of vegetable. Those remarkable non-shitting non-straying cattle and sheep seem to be of a similar breed.
I've already spent too much time thinking about imaginary sheep and cows on imaginary lawns in Scotland. One last question: where do the animals get water? A little undescribed stream next to the castle? Water trough?
*shrug* Elizabeth Bear doesn't say. But I would guess there's a water trough, because she does specify that the watercourse near the castle runs through marsh and sometimes floods.
