rocking horse vs workhorse

rocking horse

noun
  • a child’s toy consisting of a (usually wooden) horse mounted on a rocker or swing 

workhorse

noun
  • A horse used primarily for manual labor; a draft horse. 

  • Anyone or anything that does a lot of work; something or someone who works consistently or regularly. 

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