The Collaborative International Dictionary of English v.0.48:

Bestialize \Bes"tial*ize\, v. t. [imp. & p. p. Bestialized; p.
   pr. & vb. n. Bestializing.]
   To make bestial, or like a beast; to degrade; to brutalize.
   [1913 Webster]

         The process of bestializing humanity.    --Hare.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bestialize
    v 1: make brutal and depraved; give animal-like qualities to
         [syn: bestialize, bestialise]