The ear is divided into three portions: the outer, the middle, and the inner ear. The outer ear is the visible portion that can be a strong indicator of the general mood of your horse, a tip-off as to where its attention is directed, and even a sentinel to a well-timed kick. The outer ear is also called the auricle or pinna—the word auricular often refers to the ear or structures associated with it. The stiffness and shape of the outer ear are created by a large amount of cartilage. In fact, most of the outer ear is made up of cartilage with its thin covering of skin and muscles attaching to the base. The ear canal in the horse is long and generally does not allow the examination of the ear drum as can be done in people and other smaller animals. The ear drum—technically called the tympanic membrane—lies at the end of the ear canal; it is the membrane that picks up sound waves and starts the process of hearing.
On the inner side of the tympanic membrane starts the middle ear (tympanic cavity), which contains the three smallest bones in the body: the malleus, incus, and stapes (Latin for hammer, anvil, and stirrup, respectively). The malleus has one end attached to the tympanic membrane and starts a chain with the other bones attached end to end. The end of the stapes sits on a deeper membrane that separates the middle ear from the inner ear.
Within the inner ear is a complicated labyrinth of channels that are fluid-filled. The channels are lined with thousands of sensory cells that signal both the auditory nerve (involved with hearing) and the vestibular nerve (involved with balance). It is via this complex and delicate system that sound waves are transmitted to the brain and become what we hear.
Basic Equine Ear
As most of us know, every horse is different in regard to how it responds to its ears being messed with. Some of this probably is just individualism, and some is a response to a memory of an evil ear demon (often by the name of clippers). A horse with "problem" ears can be a frustrating, difficult, and sometimes dangerous animal with which to work. I’ve had horses which were weird about someone messing with their ears toss their heads so fast and violently (over a simple task such as putting a halter on) that a black eye (mine) was the end result. In my experience, allowing enough time to perform tasks such as bridling and making every effort to maintain your patience will have the best overall results.
With some of these horses, it will be necessary to loosen a bridle significantly before placing it over the ears, then tighten it up after you get it on the head. In some horses, you might have to take the bridle apart completely and reassemble it on the horse’s head so you’ll never have to go over the ears at all. With the appropriate investment of energy, you should be able to get most of these horses over their ear phobia, but bear in mind that some will never get over it. If you have the treat of raising your own horse, many of these ear problems can be avoided by making sure that the foal/weanling/yearling is accustomed to having its ears manipulated.
Clipping the equine ear can be a tough job in many regular horses, but can be nearly impossible in the ear-sensitive horse. The application of a twitch is sometimes all that’s necessary. In addition, the placement of some cotton in the ear can help reduce the irritation from noise.
Sedation can be a good option for such horses, but remember that most of the sedative drugs for horses increase the sensitivity to noise, so, again, cotton placed in the ears might help. In addition, be careful only to clip what should be clipped. As will be mentioned below, the long hair on the inner surface of the ear plays an important role in protection, and removing it needlessly can cause hours of added misery to your companion during fly season.
The Ear As A Twitch
It is not uncommon to grab (with your hand) the ear of a badly behaving horse in an effort to make him stand still. The ear can be an extremely effective "restraint" mechanism—but be careful. Some horses respond violently to the grabbing of an ear and might become worse or smack you in the head. This also might not be the best move for an ear shy/head shy horse which you are trying to retrain about its head/ears.
I have observed situations where people have placed a twitch on the ear. The restraint has been amazing, but I think this act risks permanent damage to the ear. There are a great number of nerves in the base of the ear that if damaged, could result in a permanently droopy/floppy ear. Also, if the cartilage is damaged, the ear can become permanently disfigured. It is best to reserve the twitches for the muzzle.
Flies, Flies, Flies
Flies are a significant cause of equine turmoil. One of the best treats for a mid-summer horse fly is a naked ear! It is best, if at all possible, to leave the hair on the inside of a horse’s ear as long as possible. These long hairs can be a significant barrier to one of the more sensitive areas of your horse’s body. In addition, the application of petroleum jelly to the inner surface of the ear can act as a barrier affording some protection. Of course, there are many fly sprays on the market.
A word of warning regarding fly sprays, ointments, gels, tags, collars, and wipes—some horses are more sensitive to these than others. Be careful not to apply a concentrated fly repellent to the inner surface of the ear. Read the label carefully and make the full dilution recommended before using any insect repellent. Even "natural" products, such as citronella, can be irritating. Apply any new product sparingly and observe carefully for any sensitivity. Also, be careful not to get any of these products into the eye (the horse’s or yours).
There also is a variety of fly masks on the market that give some protection for the ears. I have used several of these masks with good success. I offer a word of warning that some of them can indent into the eye or become loose and fall into the eye—make sure they fit well and check on them frequently to avoid problems.
Fly Bite Dermatitis
If your horse has a hypersensitivity to fly bites—if the inside of the ear is peppered with welts during the peak of fly season—the chances are good that fly bites are related to the dermatitis. The area should be gently cleaned to remove crusted blood and other debris. Some products that can be helpful in quieting down the inflammation process include one of the over-the-counter hydrocortisone creams. Another product that can be helpful in reducing this type of inflammation and improve healing is Preparation H or one of the other generic hemorrhoid creams containing shark oil.
The best way to deal with these horses is to prevent their exposure to flies. If you have a horse which is hypersensitive to fly bites, it can be kept in during the day and turned out at night when the exposure to flies will be reduced. The aforementioned anti-fly measures also can be of help.
Aural plaques are small to medium-sized abnormalities that typically are white to gray in color and slightly raised above the surface of surrounding skin; aural plaques occur on the inner surface of the pinna. The specific cause of aural plaques is unknown. It has been hypothesized that they form as a type of "scar" tissue resulting from fly bites. It might be difficult to tell these apart from a young equine sarcoid or even a squamous cell carcinoma lesion.
Aural plaques typically remain smooth and rarely ever bleed. If the plaque peels, the skin is generally smooth and a healthy pink skin lies underneath. In addition, it is rare for the presence of these plaques to be bothersome to the horse—they are not typically painful or itch excessively. There have been many treatments proposed and tried, but none appear to have much impact on the plaques. Given the fact that aural plaques are of little consequence to the horse, they are one of those nuisance lesions that bother us more than they bother our horses.
Sarcoids are small local tumors (not really cancer—remember that the word tumor means mass) that account for approximately 30% of the tumors reported to affect the horse. There are four basic kinds of sarcoids: flat ones, proliferative (more invasive and growing) ones, friable wart-like ones, and a combination of the wart-like and proliferative ones. The specific cause of sarcoids is unknown, but most of the current evidence indicates a viral origin, and perhaps that they are the manifestation of the bovine (cow) wart virus in the horse.
There does not appear to be any breed or sex predisposition, although there is a relative absence of observing these tumors in the Standardbred. Many of the horses affected with sarcoids are young; furthermore 70% of affected horses are less than four years of age. One-third of affected horses have more than one on their body if they have one at all, with the head, ears, and limbs being the areas of the body most commonly afflicted.
Because of the multiple gross appearance of sarcoids and the similarity of the wart-like/proliferative sarcoids to squamous cell carcinoma (cancer), the specific diagnosis often depends on a biopsy of the lesion. Also, sarcoids can be difficult to distinguish from proud flesh (exuberant granulation tissue) and summer sores (Habronema infection). An accurate diagnosis can be important as the treatment and prognosis are very different.
The treatment of ear sarcoids is complicated by the limited amount of loose skin, making surgical resection difficult. Many times if the lesion is small and not of the wart-like/proliferative type (these are often times ulcerated and bleed easily, acting as a fly attractant), the best thing to do might be nothing. If this is the case, the lesion should be carefully monitored and protected from irritation. If the decision is made to attempt treatment, the options are varied.
Another aspect that complicates treatment is the fact that there are typically tracts of sarcoid tissue that radiate out from the lesion within the skin tissue almost like roots extending out from a tree. It is impossible to tell by gross examination how far out these "roots" extend. I remember one sarcoid that was on the sheath of a draft horse. We thought it would be simple. As this is an area that has quite a bit of "extra" skin, surgical resection should be easy and surely successful. The sarcoid was removed, as well as about two inches of normal skin surrounding the lesion. Then, two weeks later, we looked at the horse only to find approximately a dozen "baby" sarcoids growing all along the normal skin margins.
Sarcoids have been treated successfully by surgical excision followed by radiation therapy, cryotherapy (freezing), hyperthermia (burning), and the injection or application of a variety of chemotherapy agents. In addition, the injection of a bacterial product called BCG (bacille Calmette-Guerin) has been successful in causing the regression of sarcoids. Specific problems in treating ear sarcoids include extreme head-shyness following treatment, the inability to care for the ears after treatment, secondary infection with bacteria or fly larvae (maggots), and/or damage of the cartilage. The risk of cartilage damage can be great with freezing or burning techniques and can lead to disfigurement of the ear.
Squamous Cell Carcinoma
Squamous cell carcinoma is a locally invasive and particularly aggressive type of cancer. The common location of squamous cell carcinoma occurs at the sites of mucocutaneous junctions—the junction between skin and mucous membranes (like the lip). The common locations for this cancer in the horse are around the eye, around the muzzle, in the oral cavity or sinuses, on the prepuce/sheath or vulva, occasionally in the stomach or bladder, and sometimes in the ear. Ocular and genital squamous cell carcinomas probably are the most common.
Predisposing factors to the development of squamous cell carcinoma include non-pigmented skin (white-faced horses) and excessive exposure to ultraviolet light (sunlight). The average age of horses with ocular squamous cell is about nine years old, compared to four years old for equine sarcoids. The treatment for squamous cell carcinoma is not too dissimilar from that of sarcoids, and, following surgical excision, includes radiation therapy, cryotherapy (freezing), hyperthermia (burning), and the injection or application of a variety of chemotherapy agents.
The ear can be very useful in the evaluation of a newborn foal. If the ear is extremely floppy and has poor development of the cartilage at its base, prematurity or dysmaturity might be a factor. If the foal seems sick or depressed, the presence of small hemorrhages surrounding the blood vessels on the inner surface of the ear (the pinna) might be an indication of neonatal septicemia. As with any sick foal, veterinary attention should be sought immediately, given the fragile nature of foals and the speed with which their illnesses can progress.
The Droopy Ear
As with most things about the body, the ears should be symmetrical. If one ear is droopy (usually flopped to the side), it is an indication of paralysis of the seventh cranial nerve (the facial nerve). The damage that caused the paralysis can occur in the brain itself or anywhere on the nerve between the brain and the ear. Diseases such as equine protozoal myeloenecephalitis (EPM) can affect the area of the brain where the seventh cranial nerve originates, but the horse generally has other neurologic signs—EPM is not that specific. These horses also generally have signs of ataxia (incoordination).
Damage to the facial nerve can occur at the base of the ear. More typically, however, the facial nerve is damaged as it passes over the side of the head (halter buckles are a common cause of this) and the muzzle is primarily affected and is pulled away from the damaged side. These horses will not have any ataxia as the lesion is "outside" of the brain.
The Middle-Inner Ear
The inner ear plays a very important role in balance. The balance system is called the vestibular system, which starts in the brain and ends up in the inner ear. It is the eighth cranial nerve (the vestibular nerve) that transmits balance control signals from the inner ear to the brain. The anatomical parts that make up the inner ear are encased in a bone called the petrous temporal bone, which is deep under the external ear in the base of the skull.
Vestibular disease generally manifests as a loss of balance and can be caused by diseases affecting the brain (central vestibular disease) or by diseases affecting the inner-middle ear (peripheral vestibular disease). The clinical signs of vestibular disease include a tilting of the head and losses in the control of balance. Causes of central vestibular disease include EPM and other problems affecting that part of the brain.
The causes of peripheral vestibular disease are typically traumatic or caused by infection of the inner/middle ear. Inflammation of the deeper parts of the ear is called otitis media interna and is much more common in people and other species of animals than in the horse. Any head trauma that injures the petrous bone or surrounding skull can cause peripheral vestibular disease and is a more common cause of a head tilt in the horse. Any evidence of bleeding from the ear canal can support traumatic vestibular disease.
The Ear Tooth
The technical name for an ear tooth is "dentigerous cyst." The ear tooth, which is also known as an "ear fistula" or "conchal sinus," can be a cause of discharge from the base of the ear. The cyst actually is considered to be a type of tumor that has its origins in a small congenital defect involving the abnormal retention of a developmental structure that forms dental material. These cysts are relatively rare and usually are noticed during the period of active tooth development (within the first two years of life), but have been reported to occur in older horses. It is a common misconception that a horse’s teeth "grow" throughout life. The permanent teeth actually are completely formed fairly early in life then are continually "pushed" out of the skull as the horse ages and the teeth wear down.
The first clinical sign of an ear tooth is a swelling at the base on the ear. As the mass enlarges, it eventually forms a tract that connects it to the skin and the outside world. Oftentimes there is secondary bacterial infection and the discharge is white/yellow as the pus drains. As the name suggests, the cystic mass usually has a crown or root of a tooth within the cystic cavity. Because the cystic lining of the mass will continue to secrete material, the only viable treatment is surgical removal of the cystic lining and its contents.
About the Author
Lee Benson is a communications consultant, editor and freelance writer living near Orangeville, Ontario. She is the managing editor of Horse-Canada.com and Racing Quarterly magazines.
POLL: University Equine Hospitals