Perhaps a dialect word, used by Willliamson as referring to a hedgehog. It doesn’t seem to appear in the OED’s 600,000 word dictionary, but I am proud to say that a friendly vuz-peg frequents our garden almost nightly.
See also ‘errin-og’ for another quirky animal name.
Source: Henry Williamson, Tarka the Otter: His joyful water-life and death in the two rivers, illus. C.F. Tunnicliffe (Harmondsworth: Puffin Books, 1976 (1927)), p. 44