Can your horse hear you?

• Overall, deafness is rare in horses.
• It can be ruled out by electronic testing using a BAER or noting the horse’s reaction to a sudden noise (clapping your hands or banging on a metal bucket.)
• Your horse should be startled if it hears an unexpected loud sound or it should at least a twitch an ear.
• No startle reaction indicates complete deafness in both ears.
• It is impossible to diagnose deafness in a single ear without a BAER test.
• Although deaf animals generally have normal mental capacities, owners should be aware that deaf horses rely on visual and vibratory sensory information, and are more likely to be startled if special considerations of their deafness is not routinely performed.

Hearing tests are performed using a brainstem auditory evoked response, known as BAER testing.

• BAER testing is routinely performed on all newborn human babies to assess hearing ability.
• With BAER testing for horses, headphones are held over the horse’s ears (or earbuds are inserted into the ear canals.)
• A series of click noises of various intensities are generated to stimulate the auditory pathway from the ear to the brain.
• Several tiny electrode wires are inserted just under the skin over the horse’s head and are used to monitor the brain’s response to the clicking sounds.
• BAER testing takes about 15 minutes to perform.
• It is tolerated well by most horses and is often performed without sedation.
• In a horse that hears normally, the waveform of the evoked potential consists of a series of five-to-seven characteristic waves.
• In a deaf horse there is either no waveform if the deafness is in the inner ear, or a partial waveform if the deafness is due to a defect in other parts of the auditory pathway.

The first published case of confirmed deafness in a horse was a 3-year-old overo Paint gelding with a bald-face and a completely blue right eye and partial blue left eye.  Congenital deafness is more common in blue eyed, bald-faced horses, though many can still hear normally.

The investigating team (led by Dr Stewart in her previous position at Auburn University in the USA) used a BAER test to confirm deafness.

• The horse’s owners reported that they had never heard him whinny.
• He also seemed oblivious to typical horse-show noises.
• The BAER test was also performed in a normal, control horse with a series of five-wave-peaks.
• The BAER test in the suspected deaf horse showed an absence of all peaks, which confirmed deafness.
• The problem' originated in the inner ear, rather than at some point further along the auditory pathway.

Although not well documented, it appears that many horses that have been deaf from birth also do not whinney.  This is similar to complete deafness in children who can therefore never learn to talk.

Horse's coat patterns and deafness

• Congenital deafness occurs in some paint horses with splashed white or frame overo coat patterns.
• Some splashed white horses with a bald white face or an extremely wide blaze, with blue eyes and variable white markings on the legs and body can be born deaf.
• Researchers have identified three separate genetic mutations that can produce the pattern in Paints and Quarter Horses
• One of the defects also occurs in Trakehners, Morgans and a few other breeds.

Genetic mutations for deafness

• Horses can be tested for the splashed white mutations by sending a hair sample to The University of California, Davis, (USA) for a genetic test.
• During development, these horse's genes suppress pigment-producing cells called melanocytes, which results in patches of pink skin with white hair and potentially blue eyes.
• If the lack of pigment extends into the inner ear it affects the sound-sensitive hair cells (cilia) and leads to deafness.
• Pure white (or white with a small brown spot) foals that are born from two Overo Paint parents can be affected by a ‘lethal white’ gene.
• These foals are deaf, which would be a minor problem, however the genetic defect also affects the nervous system resulting in an inability to move food along the gastrointestinal tract, which ultimately results in severe bloat, signs of colic and failure to pass meconium or other faecal matter.
• The genetic defect is lethal and such foals should be humanely euthanised.

• In horses with a white face and blue eyes, hearing should be tested as part of a pre-purchase examination.
• However, although deafness should be noted, it is not necessarily a reason not to purchase the horse. Deafness may be advantageous rather than a handicap, because the horse won’t ever spook because of noises. However, it may spook if something suddenly touches it or enters its field of vision without warning.
• Similar to deafness in people, deaf horses often develop heightened perceptions of their other senses, such as sight and smell.
• Obviously the horse can not be trained to voice commands, but many deaf horses have had very successful show careers.
• ‘Colonels Smokingun,’ or ‘Gunner’ for short, was a famous United States reining champion.
• He had a bald face, blue eyes and had been deaf since birth, yet won $177,226 USD in a stellar career.
• As a popular breeding stallion he frequently passed on his classic white head, blue eyes and congenital deafness.
• Blue eyed Paint horses that are deaf can be diagnosed from birth.
• Accurate BAEP recordings can be performed successfully in 2- to 4-day-old foals.