We should expect that a horse’s experiences of the world are very different than ours. We know that dogs can hear ultrasound — sounds higher than the range of human hearing — and that elephants can hear infrasound — sounds lower than the range of human hearing. We have learned that bees and birds and butterflies see ultraviolet light, and that a male silkworm can detect a female over 6 miles away. We know that birds can fly by the stars, and can sense magnetic fields. And so we have reason to suspect big differences between horse sense and human sense.
Much of our species’ early development was in the trees, in heavy vegetation. Horses developed on the plains, in open habitat. Humans ate fruit, and needed color vision to determine what was ripe. Horses ate grass, and didn’t need red at all. Humans hunted, and needed to be able to focus on selected prey. Horses were adept at running away from predators, but had to spot them first, somewhere on a 360 degree horizon. Our sensory systems evolved to give us what we needed, with few luxuries. So we would expect that the vision, hearing, and smell of humans and horses might greatly differ.
The immense field of view of the horse may underlie your horse’s apparent short attention span. The more a horse can see, the less it focuses. The more it can see, the more distracted it becomes. Blinders or blinkers are very useful for horses with important jobs, like racing or pulling carts and wagons. By narrowing the field of view to just what is in front, we eliminate the distractions. Of course, this heaps more responsibility on us to ensure that there are no dangers coming that the horse can now not see.
The binocular vision directly in front of the horse’s nose benefits him when he is grazing, which is most of the time. When he’s watching the grass, his peripheral vision — which is monocular — is at work watching for danger. He’s perfectly designed for being watchful while dining.
The external ears of a horse or mule — the pinnae (singular: pinna) — are much larger than ours. And unlike ours, they can be turned to focus on the source of a sound. When your horse spooks on the trail and freezes, he will turn his ears toward the source of the alarming sound he just heard. Watch those ears, and you will know where the sound came from, even if you didn’t hear it yourself.
Horses differ in what they then do with the information in what they hear. Some “bombproof” horses may not change their behavior at all. Other more reactive horses may stop in the tracks, raise their heads, freeze their body position, and wait. On receipt of further alarming information, a reactive horse may turn and move in the opposite direction from the sound.
Even if words fail us in talking about chemicals, olfactory receptors don’t let us down. In a mammal’s nose, each olfactory neuron possesses a single type of receptor; each receptor responds to several molecules, and each molecule is recognized by several receptors. Scents are discriminated by various combinations of 10 or more receptors. With 350 types of receptors, the number of ways you can produce combinations of 10 is ridiculous. As I’ll show you later in this chapter, a horse can detect about 1,816,285,375,084,304,096,155,409,990,400 different scents. That is about 1,699,868,436,439,970,000,000,000,000,000 more scents than your dog. And it is more than the number of chemical compounds possible. The perfect nose could detect stuff that doesn’t even exist! My old nose doesn’t do so well, but the nasal cavities of Mr. Horse are filled with possibilities.
Touch is very important to your horse. It is the main way that you communicate with him when you are on his back. Horses bond through touch, and relax when they are touched by a loving partner. And because his vision up close is very poor, touch becomes very important to him when you are up close.
The importance of touch is made clear when we learn that his side, where you might have once kicked him, is more sensitive even than a human fingertip or the calf of your leg, and that he can react to a touch that would be too light for you to feel at all.