are you sure its not just because horses, being horses, weren't just excited to be in a paddock and went charging around to have some fun? Our horses did that once and they were puffing so hard and really sweaty when we brought them back in. Just a thought.
When I bestride him, I soar, I am a hawk: he trots the air; the earth sings when he touches it; the basest horn of his hoof is more musical than the pipe of Hermes. ~William Shakespeare