In the United States and Britain, fancy (aka domesticated) mice experienced a surge in popularity in the early 20th century, with people keeping them for pets and breeding interesting specimens ...

In fact, part of why scientists adopted mice early on as a model system is because people were already breeding “fancy mice” as pets. As a result, methods for keeping and breeding them were known.

RATS AND MICE PETS AT THE POULTRY SHOW; Fancy Rodents Share the Honors with Cats and Chickens. Share full article. Dec. 2, 1904. Credit... The New York Times Archives.