American Miniature Jersey
Miniature Jerseys,as well as all Jerseys, are descendants of the original Jerseys imported from the Isle of Jersey and Britain many years ago. The breed has been carefully maintained in it’s original form on the Isle of Jersey, and stands about 44″-48″ tall. Somewhere along the line, some breeders (off the Isle) bred down in size and some bred up in size. In the US now, to differentiate them from the upsized modern-day Jerseys, these smaller cattle have been renamed the American Miniature Jersey. They maintain the Jersey conformation, color and good milk production, but in a significantly smaller package.
Foundation Miniature Jerseys are classified as being under 42″ in height. Animals between 42″ and 46″ in height are classified as Mid-size Jerseys.
More info about the breed and other resource.