heifer vs water buffalo

heifer

noun
  • A cow: a large, unattractive, unpleasant woman. 

  • A young female cow, (particularly) one over one year old but which has not calved. 

water buffalo

noun
  • A large ungulate, widely used as a domestic animal in Asia, South America. North Africa and Europe: Bubalus bubalis. 

  • A water tank mounted on a trailer to be towed by a motor vehicle. 

How often have the words heifer and water buffalo occurred in a corpus of books? (source: Google Ngram Viewer )