Page 113 - August 2022

EQUINE HEALTH
“There hasn’t been a lot of research done on equine ears and hearing. Rats, cats, and small animals are fairly easy to work with, but it’s not as convenient to bring a horse into a soundproof chamber... They are not commonly used as laboratory animals,” - Rickye Heffner
- such as twitching of the ears and the horse’s flight reaction - as indicators that horses heard sounds generated with an audio oscillator. “The purpose of that study was to determine the range of frequencies to which horses would respond, and no attempt was made to obtain thresholds for detection of sound,” says Timney.
Much of the research involving what horses hear - high or low frequency, and also the most complete data on their sound localization was done by the husband and wife team of Harry E. Heffner and Rickye S. Heffner during the 1980’s and 1990’s. Today, they are both Professors of Psychology at University
of Toledo (Ohio), and still specializing in mammalian hearing. “There hasn’t been a lot of research done on equine ears and hearing. Rats, cats, and small animals are fairly easy to work with, but it’s not as convenient to bring a horse into a soundproof chamber. You also have to train them. They are not commonly used as laboratory animals,” Rickye says.
“When we did our study with horses in the early 1980’s, we first modified a dairy barn to make it more sound-proof. It was out in the country where there was very little noise. We worked with several horses in that modified barn for more than a year, and later some ponies. We
wouldn’t be able to do that today, however, with all the animal-care regulations and increased bureaucracy,” explains Rickye. Research today is conducted with animal rights issues in mind and can be thwarted because of cost.
WHAT THE HORSE HEARS
“The basic sounds that horses detect are similar to those heard by humans, except horses can hear at higher frequencies than we do. Healthy young humans can hear up to about 18 kilohertz, maybe 20 kilohertz. Horses, however, can hear up to 35 kilohertz, which is another 2/3 of an octave or more. Thus, they can hear higher pitched noises than we can, but not as high as a dog or cat can hear,” explains Rickye. Cows and horses have about the same abilities to hear high-pitched sounds.
“Cats and cows are the most sensitive mammals when it comes to detecting very soft sounds (low intensities). Detecting soft sounds in the most sensitive part of the hearing range is a separate ability than hearing high frequency sounds,” she says. The sounds a horse hears best, he still doesn’t hear as well as a cow or
a cat. In the middle part of the hearing range where all animals hear best, cows and cats are more sensitive than horses. Cows and cats have
the very best hearing for high-pitched sounds. Horses have independently mobile ears and
can turn them in separate directions. This probably helps them focus on a sound and screen out background noise. It’s like an old- fashioned ear horn, before the days of hearing aids. The funnel-shaped ear gathers sound and shields the sound the horse is trying to focus
on from being diluted by other noises in the environment. This is like cupping your hand behind your ear to screen out wind noise or any sounds coming from behind you.
“Horses don’t localize high pitched sounds very well. A horse can hear a high-pitched whistle but may not know where it’s coming from. He may prick his ears or rotate his
ears searching for the direction of a sound. Low-pitched sounds are heard better, but once againhorses are not good localizers. Animals adapted to living out on the plains with broad horizons have eyes on the sides of their head so they can see a wide angle. Because they see so well—practically 360 degrees—their ears don’t have to be as accurate to tell them where to look for the source of a sound,” she explains. They depend more on their vision to locate potential danger.
WHY THE HORSE HEARS CERTAIN
Horses have independently mobile ears and can turn them in Since horses are not good sound localizers, they depend more on separate directions. vision. Their ears tell them where to focus their visual attention.
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