Headshakers Test Patience And Sleuthing

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Headshakers are horses that make violent repetitive up-and-down (or sometimes side-to-side) movements of their heads when they are ridden. Some horses headshake only in the sun, others at all times.

This problem has been with us for a long time, but in recent years seems to be growing in recognition, or frequency, or both. Whether it is a medical problem or a behavior/training problem isn’t always clear, but it is one of the most perplexing problems of performance horses.

Obviously, the first step in dealing with headshaking is to attempt to determine if it is behavioral or has a medical cause. In either case, the place to start is with a good history of how the problem developed.

Behavioral headshaking often gradually escalates over time. In other words, the horse tries this evasion, does not receive a sufficiently clear or emphatic correction, and therefore tries his/her luck with it again and again until it becomes a habit. Young horses and older animals with a “don’t try to tell me what to do” attitude are typical offenders. Another characteristic is that the behavior changes significantly — for better or worse — with different riders. If it appears to be behavioral, the handler should resist fighting back and continue to insist on the response he wants with correct driving aids.

If you suspect a medical cause, you’ll need a good history and thorough examination with diagnostic tests (see sidebar, page 7) to formulate an effective treatment plan.

Physical causes tend to have these general characteristics:

• Uncontrollable/involuntary nature — Horse going quietly, often under low-stress situation when he suddenly begins violent head movements. This is described as the horse acting as if he had just been attacked by a swarm of biting flies.

• A seasonal pattern to the horse’s headshaking behavior.

• Behavior triggered by bright light but disappears when worked out of the sun (horses often try to shield their heads from the sun when they are turned out in the field).

Physical Causes
Equipment Related: Although few cases actually turn out to be related to ill-fitting gear, eliminate this cause first. Begin by checking for signs of rubbing/pressure on all your tack. Also check for abnormal sensitivity by applying firm finger pressure along all areas of the poll and face that contact the bridle.

The head contains many superficial nerves, any one of which could be easily irritated. If such an area is found, your veterinarian can use local anesthesia to block sensation before you ride to see if the problem then disappears.

Check for the obvious with equipment fit (bit wrong size or not positioned in mouth correctly, pressure across poll) and experiment with different settings of the noseband, padding or different nosebands. Longe the horse with the new adjustments and allow about a week to determine if there is actually any improvement in the behavior.

One medical problem that has been connected to headshaking and might be aggravated by an ill-fitting bridle is ear mites, which can be difficult to diagnose as they live deep within the ear canal. Mite infestations often make the horse more sensitive to manipulation of the ears.

Pressure on the ears from the bridle could trigger headshaking. If the horse also habitually carries or tilts his head to one side or preferentially rubs one side of his head, a problem in the horse’s ear should be consider a possibility.

Photic Headshaking: Much in the news today is photic headshaking — headshaking triggered by strong light. Most of the current studies have been performed at the Veterinary School of the University of California at Davis, under Dr. John E. Madigan.

In people, exposure to bright sunlight, particularly when going from a darkened area suddenly into a bright one, can cause uncontrollable sneezing that lasts anywhere from a few seconds to minutes. Called the ACHOO syndrome, it is often followed by a refractory period where the response will not be triggered, then will return again if the stimulus is still there.

In horses with a history of light-triggered headshaking, photic stimulation must be No. 1 on the diagnosis list. Such things as going from the barn or a wooded area into bright light triggers the behavior. A seasonal pattern is also common — occurring in late spring and early summer, when the sun is strongest.

Some horses respond favorably to wearing only a net flymask to cut the light. Whether this truly provides enough protection to block a light response or is simply distracting the horse from performing an annoying behavior is not always clear.

Other horses may require more effective light blockage, such as that provided by the Guardian Horse Face Mask (619/794-4942) that is available with sun shades and effectively blocks much of the light but without interfering with the horse’s ability to see and be ridden safely.

Horses may also respond to treatment with the drug cyproheptidine (see sidebar), an antihistamine that also has anti-serotonin and anticholinergic activity, which affect the brain. Why this drug works is not immediately obvious, but it may have something to do with complicated interactions between the light stimulus and abnormalities of the trigeminal nerve.

Cranial Nerve Problems — Trigeminal Nerve: The trigeminal nerve is the fifth cranial nerve and provides sensation to the face. It has been found that cutting this nerve, or using local anesthesia to block the impulses, can abolish headshaking.

Dr. Madigan has postulated that headshaking may arise from an interaction between abnormal impulses from the trigeminal nerve and the light stimulus, with possible contribution from high environmental temperatures and stress of exercise. This input would be translated in the brain so the horse experiences an unpleasant facial sensation that causes the headshaking. Abnormal trigeminal impulses may occur after an injury.

Preliminary studies also suggest that perhaps infection with EHV-1 (the herpes virus responsible for rhinopneumonitis) may result in the virus taking up residence in the trigeminal nerve where it can cause a facial pain syndrome when activated.

Allergies: The seasonal pattern highly suggests allergies. Since the increased respiratory rate and blood flow associated with exercise would likely make the condition worse, this cause is plausible. In fact, allergy-related nasal/sinus irritation is found in some headshakers.

Horses with allergy-related headshaking respond well to a short course — one or two days — of corticosteroids. A positive response puts allergy higher on the list but does not confirm it. The veterinarian could decide to continue treatment in this manner — possibly with a one to two weeks course of daily steroids followed by every-other-day therapy to decrease the potential for side effects. Antihistamines can be tried but usually do not give as complete relief as corticosteroids. Decongestants are another possible avenue to explore but the side effects of possible excitement and effects on the heart usually make this a poor choice.

Nonallergic Rhinitis: Headshaking may also be triggered by another syndrome that has a parallel in people — vasomotor or nonallergic rhinitis. In these cases, there is obvious evidence of nasal swelling and congestion but no allergic component to explain it. A familiar trigger of vasomotor rhinitis is cold — the way your nose starts running when you are outside in the cold air.

Previous nasal-area trauma and deviation of the septum of cartilage inside the nose to one side seems to predispose to this problem in people and may play a role in horses as well. Evidence of increased nasal drainage (usually clear) should be evident. Pay attention to such things as level of air pollution and relative humidity to see if they influence the problem. Treatment is similar to allergic rhinitis.

Spinal Problems: The re are reports of headshaking being alleviated by chiropractic manipulations of the cervical (neck) spine. This becomes more believable when you realize that the nerves of the autonomic nervous system (the system regulating such things as reflex reactions to irritants) travel in intimate association with the spine.

Spinal misalignments may also cause swelling and “pinching” of sensory nerves that could be more painful with the head and neck in certain positions. While we do not suggest you try spinal manipulations without an exhaustive search for other causes first, disorders of the cervical spine could account for some headshaking.

Other Physical Causes: Many things can go wrong in the horse’s head, resulting in irritation, pain or pressure and ultimately to headshaking. Headshaking has been associated with nasal infections, tooth abscesses, tumors, gutteral pouch infections, ear infections — virtually any problem in the area of the head.

Unconfirmed/Undetectable Causes: Any source of irritation, especially something that might worsen with exercise, could cause headshaking. “Floaters” are small dots/spots/wiggly patterns that appear to float before the eyes and are often worse with exercise. Tinnitus (ear ringing) could also worsen with exercise. Because the horse can’t talk, we have no way of knowing if these might be causes.

Multiple-Cause Cases: Dr. Madigan suspects a complicated interplay between the trigeminal nerve, the optic nerve, heat and stress in many cases of headshaking. A fractured or deviated nasal septum resulting in a vasomotor rhinitis would be another example of a complex cause — probably requiring correction of both the problems before the headshaking will stop.

A mixed behavioral-physical cause is also likely to be present. For example, if mouth pain caused the reaction, the horse is also likely to resist the bit in any way possible (including headshaking) to avoid having that pain aggravated. If the rider gets aggressive with her hands, the horse may well end up reacting not only to the primary cause but also to the “punishment.”

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