Breaking the silence: The impact of sound and hearing

CONSIDERING 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 up- to-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 funnel- shaped 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° 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, 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 higher- pitched 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 eardrum, middle ear, and then inner ear. When sound waves “strike” the eardrum, the thin membrane vibrates, amplifying/ intensifying the sounds waves that subsequently causes the three small bones (malleus, inca, and stapes) in the middle ear and the structures in the inner ear to vibrate. Ultimately, those vibrations are metamorphosed into electric signals that stimulate the auditory (“hearing”) nerve that helps the brain interpret the electrical signals as sound...all in the blink of an eye. Speed of sound: does noise impact behaviour and performance? Does what a horse hear on the track impact their racing performance? For most horses, absolutely. According to equine behaviourist Robert M. Miller, DVM, no horse/trainer pair can reach its full potential unless the trainer understands ten specific traits that every horse inherits. Those traits include (but are not limited to) their inbred nature for flight; their perceptio and preparedness to flee; their uber quick time between their perception of danger and their physical response; a rapid desensitisation to frightening stimuli compared to other species; and their ability to learn and remember. Hearing and sound perception are therefore important for trainers to consider, but given that horses have been evolving for about 45 million years yet domesticated for only about 5,000 years, it is no wonder that we haven’t been able to “temper” some of those natural behaviours/senses, such as responding to sound and attempting to flee. One method that has helped performance horses “fight” their natural instincts and concentrate on the task at hand is the use of earplugs. Shutting out the noise Why use earplugs in thoroughbreds? According to Kim Kelly, Hong Kong Jockey Club’s Chief Stipendiary Steward, “...the use of earplugs in races conducted by the [Hong Kong Jockey] Club is aimed at allowing for the attenuation or dampening of some of the auditory stimuli for nervous/flighty horses so as to enable them to focus during the race, whilst not completely blocking out all environmental noise/stimuli. Given the large, often vocal crowds which attend racing in this jurisdiction, the use of earplugs can result in otherwise flighty horses remaining calm, which may have a positive effect on their racing performance.” Earplugs are far more common in standardbred racehorses, but according to Greg Maltby from Maltby Stables in Ontario, Canada, and a member of the Industry Code Committee for Equine Welfare Code in Canada, earplugs play an important role in thoroughbreds as well. “Earplugs help eliminate noises in the starting gate, especially the echoes that seem to drive the horses nuts,” explains Maltby. “In horseracing, we can’t wait 1.5 years to make sure the horse is used to all the sounds on the track, so earplugs help with a horse’s flight response, to deaden it a bit. They make the horse more useful and make their experience better.” Earplug ethics? Earplugs are apparently fairly innocuous but are not permitted by certain equine associations. For example, Equine Canada states that “Horses must be shown without artificial appliances.” The British Horseracing Authority does permit earplugs; however, they stipulate: “When any horse runs in a race with earplugs of any type, such plugs must not be removed during the course of the race.” Similarly, the Hong Kong Jockey Clubs states, “Only earplugs of a design approved by the Stewards and the Veterinary Officer shall be permitted to be used on horses in races. When a horse is declared to race with earplugs, such earplugs must not be removed during the course of the race and must remain in place until after the horse has been unsaddled following the race. Earplugs shall not be used by horses wearing a hood.” Why such stringent rules regarding a simple plug of cotton (or foam or sponge)? “One reason is that certain horses, such as dressage horses, are judged on behaviour issues in addition to performance. In thoroughbreds, it simply boils down to whoever crosses the finish line first,” suggests Rick Arthur, DVM, Equine Medical Director of the California Horseracing Board. Kelly takes another stance and adds, “If a horse were to be permitted to wear a hood in conjunction with earplugs, this may result in an almost complete removal of auditory senses.” “Although there are bigger fish to fry when it comes to ethical issues in the horse industry, earplugs do effectively strip away one of a horse’s most important senses,” says Heleski. Other reasons for the different rules created by different organisations are not overt, which of course begs the question, do earplugs even work? “Barry Abrams [a multiple graded stakes winning trainer whose horses have earned over $27 million to date] claimed a difficult filly one year but as soon as he put the earplugs in she turned into a stakes winner,” recalls Arthur. Of course not all horses will turn around and become stakes winners, but Heleski notes, “There is lots of anecdotal evidence that they [earplugs] do work based on the few blogs and forums.” Even if earplugs played only a small role in Zenyatta’s career, her success story certainly suggests that they are worth trying. The final note Thoroughbred trainers don’t necessarily want to “calm their savage beasts” either in the gate or during the race, but the available data on hearing and earplugs suggests that what horses hear can impact their health, performance, and quality of life, even when we either aren’t paying attention or are unable to sense what our horses do. Musician Ray Charles once said, “I was born with music inside me. Music was one of my parts. Like my ribs, my kidneys, my liver, my heart. Like my blood. It was a force already within me when I arrived on the scene. It was a necessity for me, like food or water.” Thoroughbreds also have the music inside of them, but two studies suggest that some sounds, such as music, can have a negative impact on horses. The first study, “Risk Factors for Gastric Ulceration in Thoroughbred Racehorses” (available at https://rirdc.infoservices.com.au/ downloads/08-061) reported that playing a radio in the barn increased the risk of gastric ulcers. In that study, the author, Associate Professor Guy D. Lester from the School of Veterinary and Biomedical Sciences, Murdoch University in Western Australia, collected data from 402 racehorses under the care of 37 different trainers. Those horses were sedated and scoped to assess the stomach for ulcer disease and data were collected from each trainer and horse to try to identify risk factors for gastric ulceration. Lester wrote, “There were a large number of factors that significantly impacted on ulcer disease when examined... There were a number of environmental factors that were also significantly associated with gastric ulceration... Playing of a radio within the barn increased risk [of gastric ulceration].” He concluded, “These results indicate that both physiological and psychological stress may be important determinants of ulcer disease in this population.” The study author did note, however, that “Ulcer disease is clearly a multi-factorial problem. The results of this study provide trainers, owners, and veterinarians with important information regarding the prevalence and likely clinical signs of ulcer disease.” Thus, reducing environmental stress, including excessive noise, would likely be beneficial to thoroughbreds. Not all music has a detrimental impact on thoroughbreds, reports the second study (available at http:// www.thehorse.com/articles/31229/ music- genres-effect-on-horse-behavior-evaluated). According to the study authors, "The behaviours that horses showed while listening to classical (Beethoven) and country music (Hank Williams Jr.) suggested that the music had an enriching effect on the environment of the stabled horse. “Neither jazz (New Stories) nor rock music (Green Day) had the same, soothing effect. In fact, jazz and rock caused horses to show frequent, stressful behaviours – stamping, head tossing, snorting, and vocalising (whinnying) – more frequently than when no music was being played. Interestingly, none of the thoroughbreds included in the study displayed those stressful behaviours when either classical or country music was played or when there was no music. Although the horses continued to eat when listening to jazz or rock, the horses were ‘snatching at food in short bursts.’" Although it seems that Green Day won’t be “Hitchin’ a Ride” anytime soon, Heleski points out that those study results must be interpreted with caution and says, “The higher rate of ulcers was associated with radio playing but not necessarily caused by radio playing. The study points out that stables that played the radio were far less likely to turn horses out or let them have direct contact with other horses (either of which might have been the far more important factor).” Relative to the second study, Heleski explains that only eight thoroughbred geldings were included and “we are not told what background exposure they have to different types of music, and they were only observed during a 30-minute exposure to each type of music.”

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THIS ARTICLE FIRST APPEARED IN - EUROPEAN TRAINER - ISSUE 41

TRAININGWebmaster26 April 2013Health, Training, Hearing, Ear Plugs in horses, Performance, EUT41