Equine Predatory Instinct?

A few weeks ago, Evan and I were watching Liberty and Horse Behavior and Pat mentioned something about how some horses have a predatory instinct of sorts. A lot of times we see Stallions with this instinct where they will chase down a threat to their band and confront it if necessary. Perhaps predatory is not the right term to use here, as we know horses are prey animals and would never actually seek to kill as a predator would. However, I have seen horses get pretty aggressive with "predators" (dogs and cats). In the first instance, we had brought my dog to the barn with us to have some fun running around in the fields. Being curious, my dog playfully approached a young gelding, the two sniffed each other and then the colt immediately began chasing my dog. At first it looked playful, but I soon realized this horse was driving my dog using the "snaking" head position that Stallions use to run down a mare. The horse was barreling down on my dog full speed with his head down and teeth bared. Luckily my dog was able to duck under the fence after a very close call, and I still wonder to this day what would have happened. Would the young horse have trampled my dog? Would he have bit him? Killed him? We have also recently heard a story about a horse would would pick up cats by their tail and violently shake them. I'm unsure what it is that drives horses to be confrontational and engage the "fight" side of their instincts rather than the "flight" side.

A few weeks ago, Evan and I were playing with our horses and discovered that our 2 year old Curly Horse, Lilah loves to track down and ultimately stomp on things. We first noticed the behavior when our new barn cat entered the arena. Lilah, then at Liberty, was immediately drawn to the cat following it intently at the walk and trot. The cat, obviously intimidated, didn't put up with it for long before bolting out, but we were intrigued. Next, Evan grabbed a a whip with a long string used by the normals at our barn to longe their horses. What we saw next, amazed us! Evan would drag the string along the ground, much like you would to bait a cat into playing with a ball of yarn, and Lilah would stalk it and run after it until she was able to attack it with her hooves. I say attack, because what we saw was not play, it was more than that. She was literally violent with the end of the string, stomping it out as if she was trying to stomp the life out of it. We tried to capture the nature of this on video, but after a few tries, we never did see the level of violence as we saw the first time. What you see in the video is a fair second, and demonstrates this unusual tracking behavior.

I do question whether or not this behavior stems from a high play drive (more left brain behavior) or if it stems from the need to eliminate a threat in order to seek out safety (more right brain behavior). Certainly something to think about...

Edit: I re-watched the segment in Liberty and Horse behavior where Pat briefly discusses this behavior, he calls it an extreme "herding" instinct. He states that these horses will actually kill sheep and other small animals, but are also very good at being cow horses as Janine mentions in the comments below. He does not go into much detail beyond that, but I do believe it is a behavior that we can encourage the positive attributes and discourage the negative ones. -Melissa