Sporting Blood (1931)

Valued thoroughbred mare Southern Queen slips and falls in a mud puddle, breaking her leg. Before she is destroyed, she gives birth to Tommy Boy, who becomes the favorite of his owner, horse breeder Jim Rellence. Ultimately a reluctant Rellence is forced to sell the one-year old to a prominent sportsman, and Tommy enters the world of high stakes racing. He goes through a variety of owners, all of whom have their own selfish agenda for the horse. Ultimately he ends up with Ruby, the mistress of a murdered racketeer, who wants Tommy to fulfill his true potential as a stakes horse and enters him in the Kentucky Derby.