Rat Terrier
The Rat Terrier is a breed of dog that has been found on American farms for generations. Despite this heritage, the breed is only a relatively recent introduction to the American Kennel Club. Terriers have been bred on farms in many countries because of their aptitude for ridding house and, especially, barn of rats and other vermin. Dogs that survive generations living among livestock in a barn setting are generally adept at avoiding the trampling legs of horses and cattle, and the rat terrier is no exception.
Breed Standard
According to the Rat Terrier Club of America, the ideal representative of the breed is a small to medium sized terrier that is "more refined than the Jack Russell Terrier", but moderate in size and shape, "neither appearing muscle bound nor fine boned and rangy."[1]