The Collaborative International Dictionary of English v.0.48:

Standard-bred \Stand"ard-bred`\ (-br[e^]d`), a.
   Bred in conformity to a standard. Specif., applied to a
   registered trotting horse which comes up to the standard
   adopted by the National Association of Trotting-horse
   Breeders. [U. S.]
   [1913 Webster]