Headshaking is a rather innocuous name for a very serious condition. These horses violently flip and shake their heads as if being attacked by a swarm of bees, often to the point of being unable to be ridden. Many will also snort, attempt to rub their nose on their leg and may paw. Although some horses do it year round, most headshakers start in the spring and stop in the fall.
Anecdotal reports from owners who have tried it indicate that high-dose lysine can eliminate the symptoms. This may not be as far-fetched as it sounds. It’s been known for several years that latent Herpes virus infections are commonly seated in the trigeminal nerve. In people, a condition called trigeminal neuralgia causes extremely painful symptoms of electric shock like sensations or burning in the face. A latent Herpes infection involving the nerve is a known cause of this.
Owners of headshakers that responded to lysine have reported their horses began headshaking following a Herpes vaccination. Many also report their horse to be sensitive to touch along the face (usually on one side) and/or ear. Whether vaccination is involved or not is unknown. In fact, any involvement of Herpes or trigeminal nerve irritation is also unconfirmed, but lysine is a known effective treatment for Herpes symptoms in people.
Many researchers agree that an irritation and unusual sensitivity of the trigeminal nerve may be involved in many cases of headshaking, and another drug used to treat neuropathic pain, gabapentin, has also been used with some success as well.
However, there is no single universally successful treatment and there’s an excellent chance that many different things may be involved. Diagnosis of the cause is no small feat. In some horses, more than one factor may be operating, or there may be a major underlying cause that is aggravated by something else. Our chart will help you determine possible causes.
Evaluation should start with identifying what conditions trigger the response and when. The horse should be evaluated moving with and without tack, with and without a bit, with noseband changes and with different riders. If this doesn’t change anything, your vet will do a head examination. The horse’s face and ears should be checked carefully by the vet for any unusually sensitive spots. The horse should also be scoped to examine the nasal passages and gutteral pouches; have head X-rays done if indicated.
If nothing is found to explain the headshaking, the details of when your horse does it (only in the light, only in spring, etc.) may help your vet decide what treatment to try first.