New Treatment for Headshaking in Horses

All horses will shake their heads to rid themselves of flies, dust, or a minor discomfort. It is a simple reflex action. But when it is persistent, intense, almost dangerous, and the horse is jerking his head up, rubbing, blowing, or constantly shaking as though a fly flew up his nose, it’s time to take a much closer look.

Headshaking syndrome in horses is similar to facial pain syndrome in people. It is a sensation of tingling, pricking, or unpleasant nerve pain known as trigeminal neuralgia. In horses, the condition can be triggered by overactivity of various branches of the trigeminal nerve that brings sensation to the face and muzzle.

“Usually, trigeminal-mediated headshaking is sudden in onset, although may be gradual, often [seen] between the ages of six and twelve, and may be more common in geldings,” says Dr. Veronica Roberts, European specialist in equine internal medicine at the University of Bristol. “Approximately one third of horses are seasonally affected, usually spring/summer. So far, the only fact about the pathogenesis of trigeminal-mediated headshaking of which we can be sure is that the trigeminal nerve of affected horses is sensitized, firing at too low a threshold.”

According to Roberts, the syndrome occurs due to neuropathic facial pain, perhaps from a nerve disease or a change in facial sensation due to a neuropathy of the trigeminal nerve, which is the main sensory nerve to the face.

“We do not know why this neuropathy occurs or indeed what it is that goes wrong in the nerve,” she said. “The nerve appears normal when it is examined under a microscope.”

In the past, the prognosis for the condition has been poor. Some 25 percent of horses will improve, 70 percent of them with the use of a nose net. Various medications, used to some degree of success with people, have been tried on horses but with mixed, short-term results. The costly drugs, though, come with side effects including drowsiness, which prohibits the horse from competing. 

“We were involved at the University of Liverpool in developing a surgical procedure, caudal compression of the infraorbital nerve. It carries a long term approximate success rate of 50 percent, but there is a significant risk of severe side effects which may require euthanasia and about a quarter of the cases relapsed. We therefore only recommend this procedure where euthanasia is the only other option.”