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hearing,” he explains.
There isn’t much testing done in horses.
Using brain recordings often requires sedation. Horses are vulnerable to hearing loss with age, exposure to noise, and drugs that damage nerves or organs of hearing and balance.
Magdesian says that certain antibiotics, like gentamicin, can cause hearing loss in humans. Gentamicin is commonly used in horses and is suspected to cause hearing loss in horses, but no specific testing has been done to determine this.
Hearing loss almost always occurs at the highest frequencies first (high-pitched sounds) and eventually affects ability to hear sound at lower frequencies. Since horses are poor sound localizers anyway, this might be hard for the horse owner to notice. One sign of deafness would be failure to react at all (not pricking the ears toward a sound) to high-frequency sounds such as clicks.
There are some simple ways to test a horse’s hearing. If you stand just outside his range of vision and make a noise or shake a can of grain, he will not respond. A deaf horse also will not spook or show excitement or interest in sudden noises. He may be lying down asleep, and if a train goes by or some other loud noise occurs the other horses may jump or become alarmed, but the deaf horse stays asleep.
Most people who have a completely deaf horse realize the horse is deaf, but if hearing loss is subtle, you might not notice. Deaf animals become good at compensating for their disability by relying more on other senses. A twitch of the ears or turning of the head in response to sudden noises will rule out complete deafness.
Horse owners must adjust management
and training methods to accommodate a deaf horse, using visual and touching cues rather than voice cues. It is important to recognize deafness early so the horse can be handled and trained accordingly. Otherwise, you may think the animal is not responding properly and may
mistake it for a behavioral issue—thinking the horse is being stubborn.
It’s also important to take care in approaching a deaf horse, making sure you don’t startle him. Always make sure he can see you or any other approaching person, animal
or object. One advantage to deafness is that the horse is never alarmed or startled by loud noises. Some deaf horses are less spooky to ride than horses with normal hearing because deaf horses are unaware of noises around them.
GENETIC DEAFNESS IN PAINTS
Genetic deafness occurs in horses, just
as in other animals. “For instance, the gene that causes deafness in Dalmation dogs (and white, blue-eyed cats, and blue-eyed Australian shepherds that have a lot of white) occurs in many species,” says Rickye.
Research has shown that Paint or pinto horses—or any horses with blue eyes and
large white markings on the face—can be
deaf. Deafness is caused by a lack of pigment in part of the inner ear. This pigment in the cells of the cochlea of the inner ear is necessary for them to work properly. If a horse has
pink skin in the inner ear, hearing will be affected, according to Dr. Allison Stewart, Professor of Equine Internal Medicine in the Department of Clinical Sciences at the College of Veterinary Medicine,
Auburn University, Alabama. Stewart has studied hearing and deafness in horses, looking at genetic
deafness in Paints. She began her study of genetic deafness after
a young Paint gelding was brought to the veterinary clinic at Auburn University, and she had an opportunity
to test it. She was interested in equine deafness and had already been working on brainstem auditory-evoked response testing in horses with neurological disorders or brain trauma and realized that these same testing methods could detect deafness.
Genetic deafness can occur in blue-eyed horses with a large amount of white on the face, but does not affect all blue-eyed horses or all blue- eyed Paints. “It seems to occur most frequently in splashed-white frame overos,” she says. There is also an association between lack of facial pigment and deafness, in one or both ears, in several breeds of dogs, white alpacas and llamas, mink, cats and humans.
“Genetic deafness (the animal born deaf) is often associated with lack of pigment and blue eyes. The deafness is due to lack of pigment in the cochlea hair cells in the ear. If it occurs in just one ear, most people might not even notice that the horse is deaf in that ear. Unless you actually test the horse and each individual ear, partial deafness would go undetected,” she says.
Dr. Magdesian has done extensive research on coat color genetics and has also done
BAER (brainstem auditory evoked response) tests to check hearing. All the deaf horses he’s discovered have had a lot of white on their faces and at least a partial blue eye.
“Lack of hearing has been found in certain
EQUINE HEALTH
Horses are vulnerable to hearing loss with age, exposure to noise, and drugs that damage nerves or organs of hearing and balance.
Genetic deafness (the animal born deaf) is often associated with lack of pigment and blue eyes. The deafness is due to lack of pigment in the cochlea hair cells in the ear.
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