Ear Structure and Function in Horses
The ear is an organ of hearing and an organ of balance. It consists of the outer, middle, and inner ear.
The outer ear includes the pinna (the part you see that is made of cartilage and covered by skin, fur, or hair) and the ear canal. The pinna is shaped to capture sound waves and funnel them through the ear canal to the eardrum. The pinnae are mobile and can move independently of each other, allowing horses to locate multiple sounds at the same time. In general, horses hear slightly better than people and are able to hear sounds at both higher and lower frequencies. Horses are good at hearing the high-pitched squeaks or cracks associated with the stealthy approach of a predator.
The middle ear includes the eardrum and a small, air-filled chamber that contains 3 tiny bones: the hammer, anvil, and stirrup. It also includes 2 muscles, the oval window, and the eustachian tube (a small tube that connects the middle ear with the back of the nose, allowing air to enter the middle ear).
The inner ear is a complex structure that includes the cochlea (the organ of hearing) and the vestibular system (the organ of balance).
Infections of the ear and other ear disorders are less common in horses than in dogs or cats. Your veterinarian will examine your horse’s ears at every routine checkup. If the horse has a history of previous ear infections or other problems with the ear, you should provide that information to the veterinarian.
To start, your veterinarian will visually inspect the outer ears, noting any signs of inflammation, injury from trauma, swelling, secretions, or excessive ear wax. If an ear problem is suspected, he or she will then use an instrument called an otoscope to view the ear canal and, if possible, the eardrum. The anatomy of the equine ear makes it difficult for veterinarians to see the eardrum with a simple otoscope. Specialized equipment (a video otoscope or endoscope), sedation, or local nerve blocks may be necessary to allow the veterinarian a clear view of the ear drum.
If an infection is suspected, tests will be performed on samples of fluid or secretions from the ear to determine the organisms involved and the proper treatment. Infections are most commonly caused by bacteria or parasites.
A biopsy may be necessary to diagnose some types of ear disease in horses. Further tests, including x-rays, computed tomography (CT scan), magnetic resonance imaging (MRI), neurologic tests, or electronic tests, may be needed to confirm certain conditions.