Accounting - all equine businesses/farms are businesses, and need *someone* to do the books. If you don't work for one farm, you can work for a firm specializing in agricultural accounting law/regulations. You could also work for a company that makes horse stuff - like a saddlery, a tack shop, etc. You could also work for equine events/organizations/companies that go around and set up shows. Project management is also a good set of skills to have.
You could learn how to be a judge.
You could learn how to teach lessons.