HealthWatch: Headshaking

There are times when a horse can’t stop shaking or tossing its head to a seemingly inapparent sensation; such incessant behavior is known as headshaking.

Headshaking behavior is considered to be caused by overactivity of branches of the trigeminal nerve that supply sensation to the face and muzzle. A horse’s behavioral reflex causes him to flip his head, snort or sneeze, rub his head, or take evasive action. Most headshaking horses (89% of them) flip their heads vertically, according to research findings.

In general, the horse behaves as you might expect if a bee flew up its nose, making it difficult or dangerous for it to be ridden or handled.

“The specific trigger for an individual horse is variable—triggers include heat, cold, wind, dust, particles, irritant gases, moisture, dryness, pressure, or anything that stimulates and sensitizes the respiratory surface, such as allergies,” said Dr. Derek Knottenbelt of the University of Liverpool.

Bright sunlight seems to trigger headshaking behavior in half of affected individuals, termed photic headshakers.

Dr. John Madigan, a professor of veterinary medicine at the University of California, Davis, is recognized as the leading expert on equine headshaking syndrome. He emphasizes that an owner should realize headshaking comes and goes, and once gone, it’s likely to come back.

That said, he has heard of as many as 20% of cases resolving spontaneously.

Madigan emphasizes the importance of working with your veterinarian to identify whether your horse’s headshaking behavior is mediated by the trigeminal nerve or is caused by something else. Knowing this means you’ll more likely achieve therapeutic results. He emphasized, “Season certainly plays a role in headshaking syndrome. It’s usually not the owner, bridle, bit, rider, gender, technique, or athletic pursuit. Because this is a medical condition and is not necessarily behavioral, it is inappropriate to administer punishment to a horse with trigeminal-mediated pain.”

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Caring for older horses
Lameness, weight loss, colic, and equine Cushing’s syndrome are the four top reasons for euthanizing an older horse, said Dr. Catherine McGowan at the American College of Veterinary Internal Medicine Forum, held June 3-6 in Montréal, Quebec.

Horse owners in Queensland, Australia, reported 91 deaths in a survey conducted by Dr. Thomas McGowan. Of these, 11% of the deaths reflected horses found dead with the remaining 89% euthanized. Age was an important risk factor with the risk of mortality increasing by 14% per year over the age 15. Other risk factors included dietary management, historical long hair coat or delayed shedding or laboratory diagnosed equine Cushing’s syndrome, signs of dental disease (difficulty eating), colic, lameness (Grade 4/5, including laminitis), low body condition score (2.5 to 5 or less), and elevated fibrinogen.

According to McGowan, the most important risk factors included preventable or manageable conditions, including weight loss, dental disease, and equine Cushing’s syndrome.

General health screening—in particular, attention to management, diet, dental prophylaxis, and endocrine function—is important for aged horses.

Tapeworms in the Western U. S.
New data show tapeworm prevalence on West Coast farms as 17.3% in California, 36.5% in Oregon, and 25.3% in Washington. A 2003 study in equine parasitology by Dr. Craig Reinemeyer of East Tennessee Clinical Research, uncovered the high prevalence of equine tapeworms throughout the United States. That original study indicated a lower risk of tapeworm exposure on the Pacific coast compared to other areas of the country. Researchers recently repeated the study using more than 300 farms and 600 samples from across the three Western states. Owners can ensure protection by incorporating a praziquantel dewormer into their deworming program.

Excerpted from The Horse: Your Guide to Equine Health Care. Free weekly newsletters at