The Collaborative International Dictionary of English v.0.48:

anestrous \anestrous\ adj.
   1. of or pertaining to anestrus.
      [WordNet 1.5]

   2. not in a state of estrus; not in heat; -- of lower
      mammals; as, an anestrous bitch. Opposite of estrous.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

anestrous
    adj 1: of or relating to anestrus [syn: anestrous, anestric,
           anoestrous]
    2: (of lower mammals) not in a state of estrus; not in heat; "an
       anestrous bitch" [ant: estrous]