Headshaking in Horses: Simple Symptom, Complex Cause

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For the unlucky few horses that experience headshaking, the onset is often misinterpreted as a behavioral issue, or thought to be caused by an ill-fitting bridle or uncomfortable bit. But this physical ailment will persist despite changes in tack and training techniques. The symptom is simple, but the potential causes are complicated. And the cause must be found to stop it.

HOW TO SPOT A HEAD SHAKER. Headshaking can come on suddenly and go away just as fast.? Some afflicted horses will shake their head at rest, while others only do it during exercise.

Headshakers can either shake the head vertically (up-and-down), or horizontally (side-to-side), with most cases appearing as a reflex type ?jerking? motion in the horse that can best be described as what a horse would do if someone ?flicked? it in the nose.? Horses will sometimes even stomp their front feet as they nod their head in a ?up-and-down? manner.

Many who watch a horse headshake think that there must be some sort of insect trying to fly into the nose, since the horse moves its head accordingly.? Along those same lines, head shakers will often snort, sneeze, and rub their noses on their forelimbs.? This behavior can be inhibitive to riding since horses that shake during riding will literally stop mid-trot-stride and rub their nose.

In more severe cases, the horse will actually abrade or lacerate the nose or side of the face when rubbing.? Often, horses that headshake at rest will be tired and have their eyes half closed some of the time.? This fatigue is explainable by the fact that the horse cannot get a moment?s rest with this disorder.

WHAT CAUSES HEADSHAKING' Headshaking usually comes on abruptly, with many reports suggesting exercise or bright light as triggers.? Some studies indicate that the problem starts in the spring or early summer, which suggests that either longer day length or seasonal allergies can bring it on.

Of course, there are also cases reported in fall and winter, making it impossible to pin a single etiology as the main culprit of headshaking.? Headshaking in horses has been affirmatively linked to the following etiologies:

1) Problems in the guttural pouch:? This is a unique anatomic structure to the horse that is thought to assist with phonation (whinnying).? The horse has one pouch on each side of its throat latch.? it's a hollow opening that houses the bones responsible for swallowing, as well as several of the cranial nerves and the basilar blood vessels.

The guttural pouch can become infected with bacteria or fungus, which can result in irritation to the cranial nerves, thus resulting in headshaking.

2) Trigeminal Neuralgia:? The trigeminal nerve is a major nerve in the face.? Of its three branches, it's thought that excessive firing of the maxillofacial branch can lead to a tingling or ?electric shock? sensation in the nose and muzzle.

This neuralgia has been linked to bright sunlight?the same as when we sneeze when we look up at the sun.? You may hear the term ?photic headshaking? from time to time.? This is what it refers to.

3) Seasonal Rhinitis: This is a fancy way of saying ?allergies.?? Yes. Horses can get them, too, with the same runny nose, itchy eyes, and tingly sensation in the face.? These can all cause headshaking.

4) Problems in the middle ear such as infection or ear mite infestation: Although rare, these are documented causes. That said, it's far more likely that the first three causes on the list are to blame for head shaking.

5) Ocular Pain: If a horse has uveitis (also called ?Moon Blindness?) or glaucoma (swelling of the globe), these painful conditions can result in head shaking.

6) Dental Problems:? A bad tooth can cause pain, which in some instances can make a horse shake its head or rub the side of its face.

7) Idiopathic: This just basically means, ?We don't know why.?? Unfortunately, despite all we have learned about the multifactorial causes of headshaking, a subset of horses still shake their heads for unknown reasons. headshaking sidebars

TRIAL AND ERROR TREATMENT. The elusive cause(s) of headshaking must be flushed out on a trial-and-error basis.? That means you take an educated guess at the most likely cause and then work to eliminate it. This approach can cost time and money, but sometimes that is the way things go in the horse world.

Each of the problems listed can be chased down through various diagnostic modalities.

The guttural pouches can be entered with an endoscope (tube with a fiberoptic digital camera on the end of it).? If a fungal or bacterial infection is present, the camera will see it.

Trigeminal Neuralgia can be effectively treated with the injection of a drug called fluphenazine (works about 70% of the time).? If it works, You'll see positive results within 48 hours. After that, you may need to repeat it every one to four months, depending on the patient.

Seasonal rhinitis can be treated with hydroxazine (an antihistamine similar to Benadryl).? This drug can curb some of the allergy sensations that the horse feels in his nose and face.? In some instances, fluphenazine, hydroxazine and other drugs like cyproheptadine or carbamazepine are used at various combinations. If the problem is allergy-related, or somehow linked to a hyper excitable trigeminal nerve, then each horse will be different with the type and amount of medication that he needs to control it.

A veterinary physical exam can help to rule out middle ear parasite infestations, eye problems, or tooth issues.? In some instances, diagnostic equipment such as digital radiography, a tonopen (to measure the pressure in the eye), or even a computed tomography (CT) scan of the head may be needed to identify issues here.

It seems to be the case all too often that thorough physical examination comes up with nothing.

BOTTOM LINE.? Headshaking is a peculiar malady.? It can plague some horses for life, rendering them fatigued and unrideable.? Yet in others, it instantly appears one day and disappears weeks to months later as quickly as it came.? Some early research on headshaking done back in the 1990s pretty much concluded the condition was hopeless and, as is often the case, this initial work is still believed by many. Don?t listen. Since that early work, researchers have made great strides in understanding the ailment and its myriad possible causes.

Be careful when you work around headshakers and be ever mindful that they can't control the shaking and sneezing. Work with your veterinarian to try various remedies and don't be afraid to change things up and try different combinations of treatments.? It seems that no two horses respond exactly the same to recommended therapies.? Keep the faith. Many cases resolve or become less severe over time.

Article by Contributing Veterinary Editor Grant Miller, DVM.