The Science of Horse Racing: We're All Ears

May 21st, 2023

In this year’s Saudi Derby (G3) at King Abdulaziz Racecourse, American contender Havnameltdown dueled with local starter Commissioner King around the lone turn of the one-mile stakes. As Commissioner King raced on the outside of the American, jockey Luis Morales reached up and tugged a string from between the colt’s ears, pulling out the earplugs that had dampened the sounds of the race until that moment. With the influx of sensory input, Commissioner King took his stride up a notch and pressed Havnameltdown in the stretch, inching ahead in the final strides to win by a head.

The difference that the earplugs made in Commissioner King’s performance is clear, that acute awareness of the sounds around him prompting the colt to respond with the speed he needed to win. Understanding the language of a horse’s ears as well as the impact of what they hear on their behavior can help us gain insight into our athletic partners on the track and off.

All About the Ears

Despite their size in relation to you and me, horses are technically prey animals. In the wild, they are targeted by predators like bears and cougars, so horses of all breeds have evolved first to escape when threatened and second to perform the jobs that we have bred and trained them for. Their physiques, from the top of their ears to the tips of their hooves, are designed to make them agile and quick in flight. Their hearing is a significant component of that.

As with their eyes and their ability to see, horses have ears that move with greater range and ability than humans. Positioned on the top of their head, their ears are comprised of 10 muscles, allowing them to move nearly 180 degrees. Compare that to humans, whose ears have only three external muscles with far more limited movement, and to cats, who have 32(!) muscles in their ears, allowing them to hone in on sound more precisely. A horse’s ears can move independently of one another, their movement corresponding to that of the eye on the same side. So, if the ear is pointed behind the horse, then their eye is also looking behind them.

A horse’s ears are more sensitive than a human’s and can pick up a wider range of frequencies. For example, they can detect the ultrasonic shriek of a bat, which is inaudible to human ears. This greater range in frequencies is part of their evolutionary status as prey animals that must react quickly when they perceive a threat. They can also pick up sound from as far as 4 kilometers (nearly 2.5 miles) away.

In addition to hearing at higher frequencies like the shriek of the bat, horses can also hear at a much lower range. When grazing, they can detect sounds resonating via vibrations transmitted through the ground, which their teeth will pick up and then pass along to their middle ear. Their ability to detect sound at both higher and lower levels means that they can react more quickly to sound, which can surprise the humans working with them, whose hearing is not as sensitive.

The Ins and Outs of Ears

Like humans, the physical structure of a horse’s ears has both external and internal components. What we see on top of their heads are the pinnae, conical structures made of cartilage and covered with hair or skin. This leads into the ear canal, which is also externally visible. This leads to the middle ear, which includes the eardrum and a small, air-filled chamber that houses three tiny bones: the hammer, anvil, and stirrup. The middle ear also includes two muscles, the oval window, and the eustachian tube (a small tube that connects the middle ear with the back of the nose, allowing air to enter the middle ear). The inner ear is a complex structure that includes the cochlea (the organ of hearing) and the vestibular system (the organ of balance).

The pinnae channel sound into the ear canal, amplifying them on their way to the middle ear. Next, the sound waves strike the eardrum, causing it to vibrate. These vibrations travel to that chamber with the hammer, anvil, and stirrup, which form a chain that transmits those vibrations to a second membrane. From that membrane, the sound enters the inner ear, where the fluid in the cochlea vibrates and transmits that input to the auditory nerves. The brain processes the information it receives from those nerves and tells the horse how to react.

Finally, the eustachian tubes connect the middle ear with the horse’s throat, adjusting the pressure inside the ears so that the eardrum works effectively. As ears are also important to a horse’s balance, the fluid inside the inner ear helps the horse stay steady on his feet. These canals inside the cochlea feature sensory hair cells and are set at different angles, so they detect body movement and orientation within space.

While a horse’s ears do process sound and help them maintain their equilibrium, they also serve one more function: dropping some cues about their mental state to those around them.

Direction Matters

Pay attention to a horse’s ears whenever you are standing in the paddock watching them prepare for a race or when they are off the clock standing in a stall or in a paddock. If the ears are constantly moving, this horse is listening attentively to what’s around them. Ears that are soft or limp signal that the horse is relaxed. When you see their ears pointed forward or to the side, they are interested in what’s happening in those spaces. Ears pricked rigidly forward can signal anxiety, while ears that are laid back tightly against the top of the head are a signal of displeasure or aggression. At their most agitated state, the ears are laid back against their head, a sign that the humans around them need to be cautious.

In my office I have a photo of Sir Barton, the first Triple Crown winner, from his earliest days of retirement at Audley Farm in Virginia. His lead shank is in the hands of the groom in front of him, but he is looking off to the side, with one ear pricked forward and the other pointed to his right. In this pose, his ears tell us that he is interested in what is going on to the front and to the side of him, a horse aware of his surroundings yet feeling no threat from the scene. It is this pose that reminds us that even the greats are still horses, plain and simple.