Cornell University did an interesting study on horses' dietary preferences. They fed groups either free choice hay or free choice complete ration pellets. Each group was allowed to press a plate in the stall to get a serving of the other. The horses eating pellets would 'order' hay more often than the horses on hay would 'order' pellets. The pellet ration group was also persistent enough to learn to press the plate repeatedly, up to thirteen times, per serving of hay! Time spend nosing about the stall was also reduced significantly in the hay group.