You can hire employees in your equestrian center.
Each employee provides a bonus to your equestrian center while employed there. You can hire several employees simultaneously, but cannot hire a given employee several times. You can, however, extend an employee's contract before it expires.
From time to time, you may obtain expert diplomas that have a limited duration. When this happens, all the employees currently hired become expert employees while the expert diploma is active. The bonus they provide to your equestrian center is doubled.