The Collaborative International Dictionary of English v.0.48:

beefalo \beef"a*lo\ (b[=e]"f[.a]*l[-o]), n.
   a hardy breed of beef cattle derived as a cross between the
   American bison and domestic cattle, usually being genetically
   3/8 bison and 5/8 domestic bovine; -- it yields leaner beef
   than conventional breeds.
   [WordNet 1.5 +PJC]

The Collaborative International Dictionary of English v.0.48:

cattalo \cattalo\ n.
   hardy breed of cattle resulting from crossing domestic cattle
   with the American buffalo; it yields leaner beef than
   conventional breeds; it is called also beefalo.

   Syn: beefalo.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

beefalo
    n 1: hardy breed of cattle resulting from crossing domestic
         cattle with the American buffalo; yields leaner beef than
         conventional breeds [syn: cattalo, beefalo]