The stallion is feeling a greater sense of urgency in this image exhibited by the exaggerated low driving posture.
In this image the stallion is exhibiting herding or driving behavior. The posture is one of lowered head, stretched neck, ears pinned and sometimes a snake-like back and forth head movement. There is more intensity here demonstrated by the exaggerated low posture and fast gait; the stallion was feeling some sense of urgency to redirect the mares.
