Almost certainly "buggers". Several other possible options ("bastards", "balls") are used later in the book without bowdlerisation.
'Now, you damned swab, will you take that back?' 'No, I will not.'
'You oily swine! You nigger's Nancy Boy! You crawling,
sneaking, f - - bloody bastard!'
'Order!' exclaimed Mr Macgregor.
'Here, Macgregor, ...