How horses hear and hearing-related problems

Your horse is calmly chewing hay in its pasture.

Suddenly, it stops chewing, raises its head, pricks its ears, and stares intently at the horizon.

It has heard a distant sound, one that your ears are unable to detect.

Being alert to its surroundings is part of your horse’s nature, and a strong sense of hearing plays a major role in this.

In this article, two experts explain how hearing helps horses understand their environment and how to deal with hearing-related problems.

Allison J.

Stewart, BVSC, DACVIM, DACVECC, is a professor of equine internal medicine at Auburn University.

Bonnie Beaver, DVM, serves as a professor of animal behavior at Texas A&M University.

Being alert to its surroundings is part of your horse’s nature, and a strong sense of hearing plays a major role in this.

©Amy K.

Dragoo experts say horses’ hearing is not much different from yours.

You can detect sounds with a wave frequency from 20 hertz (the lowest sound) to 20,000 hertz (the highest sound); for horses, this range is from 55 hertz to 33,500 hertz.

Beaver says: “They can’t hear low sounds as well as we can, and they only hear slightly higher ones.

” Many animals, including dogs, hear higher-frequency sounds; many can hear lower sounds.

But horses are skilled at picking up faint sounds that you might easily miss and at focusing on the direction of sounds.

Their ears have the same structures that yours do, but design differences enhance these abilities.

What big ears you have These large ears make a big difference.

With their large size and cup-like shape, each outer ear (pinna) acts like a radar dish, collecting and focusing sound waves.

You have to turn your head to focus on the source of a sound, but your horse has ten muscles that can rotate each pinna through a full 180-degree arc, and it can move them independently so that one is aimed forward and the other backward.

The pinna directs sound waves into the ear canal, which amplifies them in the same way that speaking into a tube amplifies sound.

In the middle ear, sound waves strike the eardrum (tympanic membrane) and set it vibrating.

These vibrations are transmitted through the membrane to the ossicles, three small bones on the other side.

Known by their shapes as the hammer, anvil, and stirrup, these bones form a chain that passes vibrations to a second membrane that marks the beginning of the inner ear.

Horses have big ears for a reason.

With their large size and cup-like shape, the outer ears act like a radar dish, collecting and focusing sound waves.

©Amy K.

Dragoo the inner ear contains sensory organs for hearing and balance.

The hearing part of the inner ear is called the cochlea, which is shaped like a snail shell and filled with fluids that move with vibrations in the membrane.

This movement stimulates tiny hair cells (cilia) that send nerve signals to the brain.

Different hair cells are sensitive to different sound frequencies.

Inner-ear fluid also passes through the semicircular canals, which help the horse maintain its balance.

These channels are covered with sensory hair cells and are positioned at different angles, so they detect different movements such as side-to-side, up-and-down, and angled movement.

First run, then ask—a branch breaks and your horse shoots off like an arrow released from a bow.

His quick reactions when riding or handling him can be stressful, but these reactions evolved as a defense against predators.

When his ancestors were wild, horses that did not run when a branch broke were probably preyed on by lions.

Those that ran survived, and over generations, this quick reaction became part of their nature.

All horses have this basic reaction, but the response to sudden noises varies from horse to horse.

When a pebble hits the arena wall, one horse may leap 10 feet to the side while another barely changes his stride.

Beaver says: “Genetics and experience cause these differences.

Some horses are naturally more fearful, and this may have a genetic basis.

Others have not had experiences that exposed them to noisy environments, so they may overreact.

” He says: “We have not done enough hearing tests to know whether there are differences in sensitivity to sound or not.

If there are, they are probably minor.

” He added: “The best way to deal with these situations is to stay calm and move the horse away from the perceived danger.

A calm, steady rider is best for horses that tend to react, so they learn to trust the rider.

” Punishing a horse for spooking only reinforces its fear.

Using cotton or horse earplugs can reduce noises when sudden sounds are problematic.

©Amy K.

Dragoo Beaver adds that exposing the horse to sounds in non-threatening conditions is the best way to teach acceptance of them.

Desensitization and counter-conditioning techniques can help.

In desensitization, the horse is exposed to the sound in a safe and familiar environment.

(Recall Anna Sewell's Black Beauty grazing beside railroad tracks to get used to seeing and hearing the frightening sound of trains.

) In counter-conditioning, you reward the horse while it is exposed to the frightening sound, usually with treats such as pieces of carrot or feed pellets, so that it associates the sound with something pleasant.

In both techniques, it is important to start with short sessions and low sound levels, and increase the intensity only when the horse tolerates the sound.

He said: “Horses usually react to sounds individually,” so do not assume that your horse will apply what it has learned in new situations.

It may learn that the sound of the tractor preparing the arena is not a threat, but that does not mean accepting the sound of the tractor trailer approaching from behind.

Cotton or horse earplugs can reduce noises when sudden noise may be problematic—for example, when construction is taking place nearby or in a covered indoor arena where ice may suddenly slide off the roof.

(Of course, before using earplugs in competitions, check the rules for your discipline.)

) Even with earplugs, some horses are so frightened by loud noises such as thunder and fireworks that they may injure themselves (or you).

When storms are approaching (or the Fourth of July arrives), these horses are safer in their stalls.

Stuart says that hearing loss: probably many horses lose some of their hearing ability as they age, although this has not been widely tested.

Researchers in Australia recently compared the hearing ability of two groups of horses, ages 5 to 8 and 17 to 22, and found mild to moderate decreases in the older group.

(Researchers used the brainstem auditory evoked response test, or BAER, in which electrodes attached to the horse's scalp monitor the brain's response to clicking sounds.

) Humans also hear less well as they age—a lifetime of noise exposure damages the sensory receptors in the inner ear.

Bevier says that horses may be less prone than humans to hearing loss.

He says: “Horses do not live as long as humans or in similar environments [such as rock concerts and iPods].

” In everyday life, you probably will not notice mild hearing loss in your horse.

Deafness in horses is rare.

It can be ruled out with electronic tests or simply by checking the horse's reaction to a sudden sound, such as clapping or dropping a bucket.

The sound should provoke a fear response—at minimum, an ear twitch.

If the horse shows no reaction, it probably cannot hear it.

Stuart says: a congenital type of deafness in some horses occurs with the coat pattern “splashed white.”

A splashed white horse has a very broad white line or a “bald” face, often with blue eyes and variable white markings on the legs and body.

Some of these horses are born deaf.

Researchers have identified three separate genetic mutations that can produce this pattern.

Two were seen only in the Paint and Quarter Horse breeds, and a third appeared in those breeds as well as in Morgan, Trakehner, and several other breeds.

Splashed white horses have white faces and blue eyes because of the suppression of pigment-producing cells called melanocytes during development.

Stuart says: if the lack of pigment reaches the inner ear, it affects sound-sensitive hair cells and leads to deafness.

Not all white markings are associated with a risk of deafness, and horses can be tested for Splashed white mutations.

(The University of California, Davis, offers a test.

) Stuart says: hearing should be tested as part of the pre-purchase exam.

But he points out that deafness is not a major handicap for a horse.

Because a deaf horse cannot hear what is going on around him, he is clearly not afraid of sounds, but he may be startled if something suddenly touches him or appears in his field of vision without warning.

He said: “Usually it is not a problem if you do not approach the horse from behind.

” Bevier agrees.

He said: “Hearing is often an early or secondary warning system for potential predators, and that is not a major factor for most horses today.

» he added: “It may be necessary to change your auxiliary methods — ‘clearly things like “whoa” don’t work’ — but most deaf horses adapt well.

Many of them have been successful in show competitions.

Pina problems The most common ear problems in horses are skin problems that affect the Pinna.

Fly bites.

Black flies and other biting flies love horses' ears, and the bite site can become inflamed, scabby, itchy, and sometimes infected.

Use a topical antibiotic ointment to help control infection while the bites heal.

Keep flies away by using repellents, a fly mask with ear coverage for turnout, and an ear bonnet when riding.

Avoid trimming ear hair unless you have to do it to treat an infection — the hair helps protect the skin from bites.

Aural plaques.

Aural plaques are flat, scabby, white growths that appear on the inner (concave) surface of the Pinna.

They are caused by papillomaviruses that are often transmitted by biting black flies.

Stuart says: “Ignore them.

” Although plaques do not look pretty, they do not harm the horse.

Trying to remove them usually causes a great deal of discomfort, making the horse sensitive to having its ears handled.

Use the steps above to prevent black flies from reaching the ears.

These flies are most active around dawn and dusk, so keep the horse inside during those times.

Sarcoids.

Stuart says: the ears are a prime site for these common skin tumors.

Sarcoids are not malignant, but they can grow aggressively.

They can appear as hairless, scabby areas, hard bumps under the skin, or warty or fleshy growths.

Some become raw and irritated, and some grow into large, cauliflower-like masses.

It is thought that infection with bovine papillomavirus, which causes warts in cattle, may stimulate their growth.

Stuart says: “Sarcoids look unsightly, but we usually leave them alone unless they get so big that they create a problem for the horse.

” There are various treatments — surgery, cryotherapy (freezing), chemotherapy, radiotherapy, and so on — but none are guaranteed, and the tumors tend to grow back.

He said: “Treatment is generally 70 percent successful.

You may need to retreat it several times.

The horse may become very upset by having its ears handled, and its ear may become deformed.

” So far no one has found a way to prevent sarcoids.

However, good fly control may help, since flies can transmit the virus.

Treatment with the chemotherapy drug cisplatin seems to slow the regrowth of these tumors.

This drug is administered by injection or released through implanted beads.

Deep problems If a horse has a problem deep in the ear, it may shake its head or hold the affected ear at a strange angle, tilting it downward, because it is irritated.

It may also be upset by having its ear touched, but this is not a reliable sign.

Beyer says: “The ears are sensitive and naturally something that should be protected.

If a horse has had a painful experience or has been handled incorrectly, especially when clipping, it can intensify avoidant behavior.

» Ask your veterinarian to examine the ear.

Stuart says that even with an otoscope, a device used in many animals and people, it is difficult to see inside the ear canal because the horse’s ear canal has a 90-degree bend.

The veterinarian can get a better view by using a small, flexible endoscope.

The examination may reveal the following: ticks.

Ticks can infest the ear canal as well as the pinna.

A type of tick found in the southwest, known as the spinous ear tick, is particularly known for this; infestation with these ticks can cause pain, inflammation, and sometimes even muscle spasm.

To find and remove the ticks, the horse must be heavily sedated.

Mites: These tiny relatives of ticks can also enter the ear canal, although they are less common in horses than in some other animals.

Treatment with ivermectin can help control them.

Infection: Ear canal infections of the kind that bother dogs and cats are very rare in horses.

Stuart says: "I haven't seen one in 20 years.

In a small-animal practice, you'd expect to see one every day.

" However, bacterial infections can result from tick infestation.

They are treated with topical and systemic medications.

Middle ear infections are also very rare in horses, but they do occur.

Infection can spread through the respiratory system via the Eustachian tubes, which connect the middle ear to the pharynx, or the guttural pouches, which open from the Eustachian tubes.

It can also reach the middle ear from the external ear canal or through the bloodstream.

These infections are treated with systemic antibiotics.

Horse ear talk Horses use body language to communicate with each other.

Head and body position, facial expressions, and tail movements all convey a lot of messages.

But to quickly understand what a horse is thinking, just look at its ears.

It said, "What is this?"

©Amy K.

Dragoo It said, "I don't think I like this."

©Amy K.

Dragoo It said, "I'm listening!

What's next?"

©Alana Harrison Ears loosely to the sides: It said, "I'm just resting."

It is calm.

Ears pricked forward: It said, "What's going on?"

If what it hears is really interesting (or worrying), it will turn toward the sound and remain fixed in place.

Ears back: It said, "I don't like this."

It may be worried, scared, or upset.

Ears pinned back completely: It said, "Get out of my space!"

It is serious.

Ears moving forward and back: It said, "A lot is happening here."

Continuous movement is the horse’s default ear state, which helps it keep an eye on its surroundings.

Rapid movement can indicate nervousness; you often see this when the horse is in a new environment with unfamiliar sounds.

One ear back: It said, "I'm listening."

It may pay attention with one ear to a rider or another horse approaching from behind, while still monitoring its surroundings with the other ear.

Ears drooping: It said, "I have disconnected from the environment.

» The ears may be drooped when the horse is dozing, under the influence of medication, or sick.

This can also be a sign of submission.

For more information: learn how to strengthen your fly control program to prevent your horse from being bothered (including its ears) by flies in the summer here.

This article was published in the November 2014 issue of Practical Horseman magazine.

Source: Practical Horseman – Health

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