VOICES OF EXPERIENCE

Managing a horse with trigeminal-mediated headshaking can be frustrating. The problem occurs in horses of virtually all breeds, disciplines, ages and genders.

Researchers have determined that an oversensitivity of the trigeminal nerve is the likely cause of neuropathic pain in an affected horse’s face, triggering the evasive behavior. But they still don’t understand why the nerve misfires. Until more is learned about this dysfunction—and, of course, ways to prevent it—there will be no “cure” for this type of headshaking.

In the meantime, it’s important to determine whether something else is causing the behavior. If a horse starts headshaking, ask your veterinarian to examine him for tooth abscesses, guttural pouch infections, tumors or other issues that might cause pain or discomfort in or around the head. It’s also a good idea to check the horse’s tack for fit. In cases like these, eliminating the underlying problem is likely to stop the behavior.

When other potential causes have been ruled out, however, headshaking is considered neuropathic and associated with an overly reactive trigeminal nerve. At this point, it’s helpful to begin a journal of the headshaking incidents you observe. This can help identify patterns in the behavior and perhaps pinpoint the triggers for your horse.

The specific triggers that cause neuropathic headshaking vary among affected horses. More than half are “photic headshakers,” meaning that the behavior occurs when they are exposed to bright sunlight. Photic headshakers are more likely to be worse in the spring and summer months; the attacks may ease or stop entirely on overcast or rainy days or during the fall and winter. About 50 percent of affected horses show the behavior only during exercise, with or without a rider. Other triggers can include exposure to the wind as well as loud noises or smells.

Therein lies a problem: A number of treatments and management strategies can help to alleviate the signs of headshaking, but because the triggers can vary from horse to horse, there is no one approach that is effective for all cases. It generally takes some trial and error to find a strategy that might work with each affected horse. Here are some of the approaches owners have tried:

• Management changes are often a good place to start. If headshaking is most pronounced when the horse is outside in direct sunlight, the best option might be to keep him inside during the day and turn him out only at night. A fly mask that blocks high levels of ultraviolet radiation might also be helpful.

• Physical coverings, such as nose nets, mesh sheets for a horse’s muzzle or devices that dangle over a horse’s nostrils, can help to reduce headshaking in some horses who are triggered by exercise. How they help isn’t clear, but in one trial with 36 owners, 75 percent reported at least some improvement with different types of nets.

When a horse’s headshaking is triggered by sunlight, a fly mask and access to shade can be helpful.

• Dietary supplements can address some triggers. Melatonin, a hormone involved in regulating the horse’s sleep-wake cycles, may help horses who are seasonally affected. Also, supplementing with magnesium, an electrolyte involved in nerve function, has been proven to be helpful. However, if you try magnesium, your veterinarian will need to perform blood tests periodically to monitor your horse’s blood levels of the mineral to guard against overdoses.

• Medications, including cyproheptadine (an antihistamine), carbamazepine (an anti-seizure drug), hydroxyzine (an antihistamine) and phenobarbital (barbiturate), have reduced headshaking in some horses; however, they all have potentially serious side effects.