Headshaking In Horses

Headshaking in horses is a mysterious condition that can manifest in various ways, from minor tics to chronic and severe shaking.

Headshaking In Horses? The cause of head shaking in horses remains a mystery, and it may be very challenging to diagnose, manage, and find a cure for the illness. There is a broad range of possible manifestations, from a minor “tic” that only occurs sometimes to chronic and often severe head shaking. The shaking of the head manifests itself most often in a horizontal or vertical plane, although it may also occur in a vertical plane. The vibration of the head is involuntary, and while we do not understand a significant amount about the illness, we are aware that it is a painful condition that, in its most extreme form, might justify euthanasia.

Causes of Headshaking in Horses

Headshaking In Horses

Horses may show headshaking behavior due to various factors such as dental issues, nerve damage, improper equipment, sinusitis, eye disease, or ear mite infestation. However, when we refer to headshaking, we usually mean idiopathic headshaking. Approximately 2% of horses in the UK suffer with idiopathic headshaking, which may potentially impact up to 6% of horses.

Idiopathic Headshaking

Idiopathic is a broad word for a sickness that manifests suddenly without apparent explanation. Put differently, idiopathic headshaking refers to head shaking that has no discernible reason, not even one of the ones above. Although it is not exclusive to any breed, onset often occurs in geldings between the ages of six and nine. The term “seasonal headshaking” originates from approximately 60% of instances occur in spring and summer and often disappear entirely in fall and winter. With time, many of these horses will become worse; their headshaking will become more noticeable and last longer each year. After much research in recent years, the correct name for idiopathic headshaking is now trigeminal mediated headshaking.

Trigeminal headshaking may include triggers (rather than causes) with touch, light (photic headshaking), and sound. Motivation is anything that induces the facial nerves to fire. Despite pollen becoming a common cause of trigeminal headshaking, the disorder appears no longer thought to have an allergic origin.

Trigeminal Mediated Headshaking

Trigeminal Mediated Headshaking

Now, we know that neuropathic pain of the trigeminal nerve causes headshaking in most idiopathic cases (trigeminal-mediated headshaking). Neuropathic pain remains the term for pain from sensory nerves that result from stimuli that would not typically cause pain.

The brain receives sensory data from the face via the trigeminal nerve. The ophthalmic nerve (the eye), the maxillary nerve (mid-face, including the nose, cheeks, and upper lip), and the mandibular nerve (the jaw) are its three main branches. One explanation for head shaking is trigeminal nerve sensitization. Studies in science (especially in the maxillary region) have shown that horses who move their heads have a lower activation threshold. This suggests that causing pain requires a lot less effort. 

This explains why everyday stimuli-like light, may result in painful shocks. Regretfully, we still don’t know why this hypersensitivity may happen.

While neuropathic pain is a well-established illness in humans, numerous causes do not correlate with horses shaking their heads. Like shingles, these viruses finally became eradicated and became widely utilized. The most similar human condition to headshaking is trigeminal neuralgia, characterized by hypersensitisation of the trigeminal nerve. But this doesn’t come from headshaking; rather, it happens when the nerve’s covering falls off.

Common genetic, physiological, and environmental variables contribute to headshaking, making the etiology complicated and challenging to investigate.

Treatment options for headshaking in horses: can drugs help?

Certain medications, such as gabapentin, are effective in treating neuropathic pain in humans but not suitable for use in horses. Antihistamine and anti-epileptic medical combinations are not permitted in horses due to licensing requirements and potential sedative side effects, despite various attempts at their use.

There is no evident improvement after using the steroid dexamethasone. Many horse owners have also experimented with homeopathy and vitamins. Still, they must stand up to thorough scientific testing, though some may have anecdotal evidence of benefit.

Neurosurgery

Neurosurgery

Most horse owners are aware of lameness therapy, which involves a neurectomy, which involves cutting off a nerve to make the horse painless. Could trigeminal-mediated headshaking benefit from this? Eighteen horses underwent the experiment in the 1980s. Three recovered, but it seriously compromised the horses’ well-being since they were no longer able to feel their faces. It was not compassionate, even if it advanced the field of veterinary medicine’s knowledge of the illness.

Coil procedures

Coil procedures

The only approved procedure for treating headshaking is implanting platinum coils behind the intraorbital canal. The locks progressively enlarge, pressing on the nerve. Under general anesthesia, it carries a high risk. It may cause discomfort for the horse and its handlers and irritate the nasal cavity and nostrils after surgery. It has a 50% success rate on average. However, significant adverse effects resulted in the death of four of the 58 horses in the trial that had the procedure. It often goes for situations in which one has no other choice but to die, and less intrusive therapy has not lessened the severe shaking.

Surgery

Some 3/19 horses benefited from a bilateral infraorbital neurectomy, but there were often significant side effects. Therefore, while it helped identify the affected nerve at the time, it isn’t an appropriate procedure today.

The caudal ablation of the infraorbital nerve by coil compression had a 50% success rate in 57 horses, but 26% relapsed within nine months. Most horses had temporary adverse effects from scratching their noses. Nevertheless, due to the severity or persistence of these negative effects, 4 out of the 58 got to sleep.

The suggestion of this procedure is often not recommended due to potential negative outcomes and the need for more effective methods.

EQUIPENS 

EquiPENS is one such therapeutic method that is now in use. Initially used in humans, this kind of neuromodulation (also known as PENS treatment) modifies nerve activity by delivering an electrical or chemical stimulation. The procedure involves inserting a skin-piercing probe across the facial nerve to provide an electrical impulse, all while the horse becomes conscious while sedated.

Of the 168 horses in the research, half had good responses, but only 25% of them had long-term remission. On the other hand, some patients who went back to headshaking could prolong their remission with further treatments.

While PENS treatments are pretty safe and don’t often cause side effects or difficulties, the cost of each treatment is high, at around £700. Initially, horses get three treatments; however, further ones can be necessary. Thus, the ordinary owner may find the expense exorbitant.

Electromuscular Therapy

The Royal Veterinary College is studying electroacupuncture, which stimulates the nerve with electric impulses. Three of the six horses in different research that used the same horses exhibited hopeful remission periods.

Electroacupuncture is a cost-effective alternative to PENS, and if thoroughly investigated, it may be a suitable choice for many owners. The surgery could end up done in the stable yard, saving the horse from having to travel.

Current research

Amino acids that stabilize neuronal membranes in humans, rats, and cats are the subject of a research project at Bristol University. Compared with other drugs, amino acids are less harmful and may compete with one another. New research from the University of California, Davis, California, has shown that giving some afflicted horses supplements of magnesium and boron will lessen their headshaking behavior.

Summary

The variable nature of this disease leaves much to be learned, with most cases occurring during lunges and tacking, and fewer horses exclusively displaying this behavior in the field or stable.

Headshaking in horses is a mysterious condition that can manifest in various ways, from minor tics to chronic and severe shaking. Ear mite infestations, sinusitis, eye conditions, ill-fitting equipment, dental problems, and nerve damage are often the causes of it.

Idiopathic headshaking, a common issue in 6% of UK horses, is often caused by trigeminal nerve neuropathic pain.

Trigeminal-mediated headshaking may include triggers with touch, light, and sound. Even though pollen became a common cause, their allergic origin was no longer considered when it became present. Treatment options for horse headshaking include medications like gabapentin, neurectomy, coil procedures, electroacupuncture, and amino acids. Neuromodulation, such as PENS treatment, modifies nerve activity by electrical or chemical stimulation. Electroacupuncture is less expensive and may be a good choice for many owners. Current research explores amino acids that stabilize neuronal membranes in humans, rats, and cats. Nevertheless, more investigation needs to happen to comprehend the cause of horses’ headshaking completely.

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