What causes headshaking in horses?
Sensitization of the trigeminal nerve running down the side of the face causes it to fire at a lower-than-normal threshold. The problem is one of neuropathic pain that is a functional rather than a structural problem. Neuropathic pain creates itching, tingling, and electric-shock-like sensations that cause a horse to jerk its head suddenly, snort, rub or strike its face, or shake its head. Many horses have an anxious facial expression in anticipation of the “electrical shock.” Many horses experience this seasonally during longer sunlight hours during spring, summer, and early fall. Exercise can be a trigger or amplify clinical signs. The specific trigger for an individual horse is variable – heat, cold, wind, dust, irritant gases, moisture, dryness, pressure, or anything that stimulates and sensitizes the face or respiratory surface, such as allergies.
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How Veterinarians Diagnose Headshaking in Horses
Affected horses move their head and neck vertically, horizontally, or in a rotational motion. Some display strong and excessive snorting, nasal or facial rubbing, or striking their nose with a foreleg. Exercise often elicits more dramatic reactions but some horses experience headshaking issues even at rest. Other causes of headshaking should be ruled out through a variety of diagnostic procedures.
A definitive diagnosis relies on a thorough history provided by the owner, along with a physical exam and videotape of the horse. Possible diagnostic tools include head radiographs, nasopharyngeal and guttural pouch endoscopy, and anesthetic nerve blocks of branches of the trigeminal nerve and/or infraorbital nerve. Other non-invasive diagnostic strategies include the temporary use of contact lenses, goggles, or eye shades to reduce light as well as the use of nasal occlusion masks.
Equine Headshaking Treatment
A number of remedies are tried: Face masks with ultraviolet light protection, nose nets, melatonin (12-16 mg at 5 pm), cyproheptadine, magnesium, transelectrical nerve stimulation, caudal compression of the infraorbital nerve, or alkalization of the blood with sodium bicarbonate to reduce headshaking by 50%. Supplementing hay with a combination of magnesium citrate (24.2 mg/kg) and boron (40 mg/kg) in a pelleted diet potentially reduces trigeminal-mediated headshaking by 64%.
Prevention: Unfortunately, prevention is not possible until a horse begins to show signs, and then preventive measures are the same as the treatment measures mentioned above.
Preventing Headshaking in Horses
Unfortunately, prevention is not possible until a horse begins to show signs, and then preventive measures are the same as the treatment measures mentioned above.
