burro vs jennet

burro

noun
  • A small donkey, especially when used as a pack animal or one that is feral and lives in the southwestern United States or northern Mexico. 

jennet

noun
  • A small Spanish horse. 

  • A female ass or donkey; a jenny. 

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