Wild Burro of the West (1960)

Dusty is a small burro living a quiet life with her elderly master, a farmer in Mexico, until two men sneak onto the farm and steal her. They use the animal to help them rustle cattle. Dusty carries their water and other supplies, but the men are cruel and mistreat the burro, allowing her little water and feed. Tired of this mistreatment, Dusty strains to break free of the hobbles used to control her. Starring Bill Keys as Andy, Bill Pace as a Rustler and Jim Burch as a Rustler.