What is a job horse and what are his duties?

A horse job would be like a stable hand, or groomers. The stable hand would be in charge of taking care of the horse's necessaries, such as food, water that sort of things), and a groomer would be in charge of making the horse look fresh and clean. They'd brush the horse and bath them and may even touch up on the horse's "shoes".

Horse races and to race and win