The Collaborative International Dictionary of English v.0.48:

Half-bred \Half"-bred`\ (-br[e^]d`), a.
   1. Half-blooded. [Obs.]
      [1913 Webster]

   2. Imperfectly acquainted with the rules of good-breeding;
      not well trained. --Atterbury.
      [1913 Webster]

WordNet (r) 3.0 (2006):

half-bred
    adj 1: (of animals) having only one purebred parent [syn: half-
           blooded, half-bred, half-breed]