Complex sentence: To pass the studbook evaluation, a riding type horse must either have placed in a Grade IV dressage or combined driving competition, or pass a dressage test; must pass a jumping evaluation and a ridability test, and possess clean gaits.
Split into simpler sentences: To pass the studbook evaluation, a riding type horse must either have placed in a Grade IV dressage or combined driving competition, or pass a dressage test. It must also pass a jumping evaluation and a ridability test, and possess clean gaits.