Understanding Horses and Their Hearing

Should a horse fail to react to auditory stimuli, such as clapping or a car back-firing, it might be wise to have your veterinarian check him for possible hearing issues. Horses, like humans, may experience hearing loss and leaving it unaddressed could lead to performance and/or behavior issues.

Although uncommon, hearing issues can occur in horses

Horses with partial hearing loss may have difficulty localizing sound. This can result in anxiety, as the horse is not able to accurately scout out its surroundings. This may go unnoticed while the horse is in familiar surroundings, however, taking a horse into a new environment could result in sudden and unusual behaviors.

Diagnosing equine hearing loss can be done through an otoscopic or ear exam, a neurological exam or by utilizing an endoscope. Or, a BAER or brainstem auditory evoked response may be used. With a neurological exam, the horse is subjected to a sound test, which is either a singular or series of loud sounds. If the horse appears to react and localize the sound appropriately, his auditory function may be fine. However, should he react to the sound but seem confused about its source, he may have partial hearing loss problems. Should the horse fail to react at all, he may be completely deaf.

With an endoscopic exam, the horse's ear structures are evaluated. Your veterinarian may elect to conduct this review under a "standing sedation," (Lightly drugging the horse while it stands in cross ties, for example,) or general anesthesia. While standing sedation is more commonly used, general anesthesia allows for a more thorough exam and is less taxing on the delicate equipment involved. Otoscopic exams are also more thorough when conducted under general anaesthesia.

The BAER or brainstem auditory evoked response involves placing tiny electrodes beneath the horse's scalp. It detects electrical activity as it progresses from the horse's inner ear, along the auditory pathway, to the brain. The horse is exposed to sounds via special insert or equine head phones.

Among the more common causes of equine hearing loss are:

  • Otitis (7%) - Inflammation of the middle ear, (Otitis media) or inflammation of the inner ear (interna), can be a catalyst in equine hearing loss.
  • Multifocal Brain Disease (23%) - While horses with brainstem diseases may have some degree of hearing loss, this is typically the least of their problems.
  • Temporohyoid Osteoarthropathy (THO, 35%) - Horses with this condition are usually in the 11 to 14 year age range and may also suffer from corneal ulcers and facial neuropathy, along with hearing loss. The issue stems from arthritic, bony growths in the horse's head.

Congenital Sensorineural Deafness (30%) - Horses with this inherited condition are found to be equally deaf in both ears. The problem is not uncommon among certain American Paint horses.

A UC Davis study on deaf horses, (Published in the AVMA Journal on American Paint Horses) discovered that paint horses of a specific lineage may be born deaf. This may be critical as many training techniques involve audio (clucking, saying whoa,) as well as leg and hand cues. However, some equestrians have found that these horses respond well to visual cues. According to Gary Megdesian, DVM at US Davis, “With visual and tactile cues, deaf horses do very well. I have owned a deaf mare for 24 years, and most people never notice that she cannot hear. I have ridden her on trails and in the arena, and have successively shown her without incident. I also know of deaf horses who are successful cutting horses and all-around Western and English show horses. One advantage of owning a deaf horse is that she will never spook in response to loud noises."

There are 3 types of coat pattern colorations found in American Paint horses, Tobiano, Tovero and Overo. All the hearing challenged horses in the UC Davis study were found to be of the Overo pattern, accompanied by splashed white or frame splashed white coloration. (The term "frame" refers to the usual appearance of white patches centered in the horse's neck and body and framed by surrounding colored areas.) The good news is that splashed white paint horses are not that common and not every Overo "splashed white" horse is deaf. If you're concerned about purchasing a potentially deaf horse, pay attention to things like white spotting on the horse's face and legs as well as eye color. Blue eyes are often associated with deafness in horses, much like it is in cats and dogs with white coats.

The BAER test is recommended when considering purchasing this type of American Paint horse. If not available through your veterinarian, contact your local veterinary college to see if BAER testing is available. While a deaf horse can still make a highly suitable companion, it's probably not a good idea to use the horse for breeding stock.

While the afore mentioned issues make up the majority of equine deafness problems, horses may also suffer auditory loss due to old age, skeletal issues or head injuries. In some cases a percentage of the horse's hearing may return. This depends on things such as: discontinuing drugs that may temporarily decrease hearing, identifying and removing lesions or simply allowing sufficient time for healing.

Hearing loss is not a terribly common problem in horses, but, if you suspect your horse may have compromised hearing, talk to your veterinarian.

 *Image courtesy of Dollar Photo Club