herdsman vs sheepdog

herdsman

noun
  • A person who tends livestock, especially cows and sheep. 

sheepdog

noun
  • A breed of dog used for guarding sheep. 

  • A breed of dog, used for herding sheep. 

  • A police officer. 

verb
  • To chaperon or shepherd. 

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