heifer vs yearling

heifer

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

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

yearling

noun
  • An animal that is between one and two years old; one that is in its second year (but not yet two full years old). 

  • A racehorse that is considered to be one year old until a subsequent January 1st. 

  • A sophomore at West Point military academy. 

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