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TRAINING
Breaking the silence: the impact of sound and hearing What your horses do (or don’t) hear might impact their performance and overall health. We all know that as prey animals horses rely heavily on their senses of sound, smell, and sight to survive, and many trainers attempt to manipulate those senses to help their horses perform maximally. Blinkers, hoods, visors, eyecovers, and other so-called “appliances” are all designed to help racehorses concentrate during a race. Even Zenyatta, 2010 Horse of the Year in the US, apparently benefitted from the use of earplugs during her 20-race career (of which she won the first 19).
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WORDS: Stacey Oke, DVM, MSc PHOtO: FRaNk SORGe ILLUStRatIONS: FeRNWOOD StUDIOS
ONSIDERING how important a horse’s sense of hearing is and how commonly earplugs are used in various athletic events, there is remarkably little research in this field. Nonetheless, this article provides the most upto-date information on the form and function of the equine ear and how hearing and sound impact performance.
How horses hear Just like most other parts of the horse’s body, the ear has been fine-tuned over the past several million years to help horses evade their natural predators. “A horse’s sense of hearing is exquisite,” says Camie Heleski, PhD, Instructor/ Coordinator of the two-year Ag Tech Horse Management Program at Michigan State University’s Department of Animal Science and a council member for the International Society for Equitation Science. This is because a horse’s ear is a funnelshaped structure designed to corral sound waves to the inner ear where they are perceived by the brain. The outer ear, called the pinna, has ten separate muscles that work in concert to rotate each ear up to 180°. As a result, a horse can effectively achieve 360°
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worth of hearing without having to move his head. In contrast, humans only have three muscles associated with each of our small, flat, essentially immobile pinnae, effectively limiting what and how much we hear. Additionally, unlike horses, our ears are not able to move independently. Not only can horses hear noises farther away than humans and perceive a larger variety of noises but horses also beat humans in the category of sound localisation. Heleski says, “According to Paul McGreevy,
“There is nothing in speech that occurs in the extreme sound ranges that horses can hear. They can hear ‘environmental’ sounds that we don’t hear, like insects” Lynne McCurdy
author of the book Equine Behavior: A Guide for Veterinarians and Equine Scientists, horses are able to locate the source of a sound within an arc of approximately 25°, and horses can respond to sounds from up to 4,400 metres away, which is just over 21 furlongs.” Some other interesting facts about what horses hear that Heleski summarized from McGreevy’s book is that horses have a much larger range of sound and can hear higherpitched sounds than humans. Specifically, the sound range in humans is quite narrow, from a lowly 20 hertz (Hz) to a mere 20,000 Hz. In contrast, horses have a much larger range of sound: 55-33,500 Hz. What does this translate to? Lynne McCurdy, a doctor of audiology in Wellington County, Ontario, Canada, explains: “250 Hz is the rumbly middle C on the piano, 20 Hz is a really low drum, and human speech sounds don’t exceed 8,000 Hz.” This means that horses can hear sounds that we can’t even fathom. “There is nothing in speech that occurs in the extreme sound ranges that horses can hear,” notes McCurdy. She adds, “They can hear ‘environmental’ sounds that we don’t hear, like insects.” Once the sound waves reach the pinnae, they are funneled through the ear canal to the