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Unlocking Pain's Puzzle

from contributor Anna Sochocky of Equi-Libris

A headshaking diagnosis in a horse can demolish a promising future as well as an owner's hope of any cure. Characterized by a horse incessantly and involuntarily thrashing or jerking its head in response to unseen stimuli, the affected animal often lives in a physical but unforeseen prison of pain and discomfort.

I know because ten years ago, my veterinarian thought my horse was a headshaker.

Leading British researcher Derek Knottenbelt, BVM and S, DVM and S, MRCVS, Dipl. ECEIM of the University of Liverpool notes that a host of “triggers” can set off a headshaking episode. According to Knottenbelt, headshaking is a “loaded gun disease” waiting for a trigger like heat, cold, wind, dust, moisture, dryness, or anything else that might stimulate and sensitize the respiratory surface to initiate a reaction. Enabling factors are thought to increase nerve activity in and around the trigeminal ganglia spawning the inappropriate "firing" of sensation in the horse's head.

I was a desperate new horse owner grasping at medical straws I did not fully understand. Yet, so many questions surfaced for me. Can my horse be exhibiting commonly recognized headshaking behavior but be suffering from another disorder? Is my horse suffering from an acute allergenic reaction to his environment? Is there a relationship between headshaking and equine allergies?

My evenings melted away as I read page after page of information about the types and causes of equine allergies, sinusitis, recurrent airway obstruction, and headshaking and its relationship to allergies. I read about traditional and alternative therapies, including acupuncture and Chinese herbs. I searched chat rooms and e-mailed other horse owners to ask what treatment options they had pursued their allergic and headshaking horses. But rather than finding answers, I grew increasingly overwhelmed, confused, and heartbroken.

I decided to have a full skin allergy panel done by an equine dermatologist. Though it can take up to a day for an allergic reaction to manifest in this test, dot after dot of puffy, red wheals sprouted on my horse’s neck within minutes. My horse was so reactive, I joked with the vet that my horse was allergic to the entire state of New Mexico. Finally, I had some answers.

Six months after starting my horse on immunotherapy, he was a new animal.

I was lucky, but so many horse owners are not and are saddled with a headshaking diagnosis. However, there is hope for both horses and the owners who love them. While the headshaking syndrome lacks a cure, pioneering new research at the University of Bristol and the University of California – Davis suggests that a more permanent management plan may be on the horizon.

Dr. Veronica Roberts, MA(Oxon), MA, VetMB (Cantab), PGCert (HE) DipECEIM MRCVS, and Senior Clinical Fellow in Equine Medicine at the University of Bristol’s School of Veterinary Sciences in the United Kingdom is charting an innovative treatment protocol which has yielded positive results. Two forms of treatment – the EquiPENS™ protocol in the UK and Europe and electroacupuncture and the role of nutrition in the United States – show promise for providing at least temporary remission from headshaking behavior in horses.

A team of University of Bristol’s School of Veterinary Sciences clinical researchers working with a neurology team at Southmead Hospital in Bristol and led by Roberts conducted a study of seven horses diagnosed with trigeminal-mediated headshaking. Results published in the Equine Veterinary Journal indicated that a new therapy called percutaneous electrical nerve stimulation, trademarked as EquiPENS™, in the United Kingdom has the potential to manage the debilitating disorder that has long stymied horse owners and veterinarians alike.

Performing the PENS protocol on 168 horses in the UK and Europe and enlisting over five hundred procedures, nearly forty percent of horses returned to their previous work level for at least two months, with others remaining asymptomatic for up to four years.

In a 2013 study from UC Davis, veterinary neurologist Monica Aleman, DVM, Ph.D., put 12 mature geldings under anesthesia and placed electrodes on their faces to measure their sensory nerves' reactions. Six of the geldings had idiopathic headshaking, and six were non-headshaking "control" geldings. The researchers found that when electrical stimulation was applied to the gums behind the study horses' upper canine teeth, the nerves of the headshakers fired at a much lower threshold than did those in the control group. The study proved that the trigeminal nerve was functioning differently in headshaking horses.

Internationally recognized equine headshaking expert John Madigan, DVM, DACVIM, of the University of California, Davis, and his team have explored how nutrition may influence headshaking. Varying blood levels of electrolytes might affect neural function. A 2018 study by UC Davis researchers tracked the effects of temporarily altering a horse's blood pH with different electrolytes levels. In horses where the blood pH was increased, headshaking behavior was reduced by fifty-eight percent compared to control horses. Changes only lasted an hour but changing a horse's chemical balance might be achieved through diet, encouraging the trigeminal nerve to act naturally.

Horse owners recognize that a headshaking diagnosis is a serious one, but scientific advancements show promise, and what was once a career-ending condition may become another treatable condition. For more information, go to the website and read the feature article about headshaking and consider joining the site’s blog, Nicker Notes. ( )

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