sentences:  Smaller gates may be used at training facilities for schooling horses, or as an auxiliary gate in addition to the main gate for large-field races such as the Kentucky Derby.The gates are suspended from an overhead welded steel truss, supported at each end by wheels with pneumatic tires.The entire structure is designed to be towed behind a tractor or truck, so that it can be moved about on the racetrack grounds, or towed over highways from place to place.