A nose net remains the simplest and arguably most effective strategy found thus far to provide relief to horses whose headshaking is caused by trigeminal nerve issues, according to a just-published review.
A nose mask is the first treatment to try as it is cheap, non-invasive, risk-free, and is allowed in most competitions at most levels, says Veronica Roberts, of the University of Bristol Veterinary School.
“It is reported to give up to 70% relief in 25% cases,” she says.
Roberts, a senior clinical fellow in equine medicine with a research interest in headshaking, says this affordable option is accepted by many competition regulatory bodies, but not all.
Trigeminal-mediated headshaking is a little-understood nerve-related facial pain condition in horses.
It may affect around 1% of the equine population to a degree that requires veterinary attention.
“As a pain condition, this represents a significant welfare issue,” says Roberts, whose review is published this week in the journal Veterinary Medicine: Research and Reports.
“Horses are usually more severely affected at exercise which can leave them unable to perform, or even dangerous to ride and handle.”
With little known about the condition and the response to treatment variable, badly affected horses are often euthanized.
Roberts says occasional shaking of the head by a horse is normal, but a pathological cause should be considered if it becomes frequent, violent, is accompanied by flicks or jerks of the head, causes nasal irritation, triggers signs of distress, or affects riding or handling of the animal.
Conditions which can cause headshaking include ear mites, cranial nerve problems, neck injury, eye disease, guttural pouch mycosis, dental issues and sinusitis.
However, there is a 98% chance that no physical cause can be identified, leading to a diagnosis of headshaking of unknown cause.
“As knowledge of this condition has developed, it is likely that most of these horses were suffering what is now termed trigeminal-mediated headshaking.”
Clinical signs tend to be seasonal in around 60% of headshaking horses, with most affected in spring or summer, although a recent study found that owners reported only a quarter of affected horses ever being completely free of signs in the off seasons.
“Even in non-seasonally affected horses, signs may vary with an apparent correlation to weather conditions,” she notes.
Signs of trigeminal-mediated headshaking are consistent with pain in the trigeminal nerve, something which was suspected even in the 19th century. Indeed, it has only been confirmed recently in research.
These studies showed that the trigeminal nerve below the eye sockets in affected horses becomes sensitized, with a lower threshold for activation than unaffected horses. The reason for this sensitization remains unknown, Roberts says.
While herpes virus is involved in some nerve-related pain syndromes in people, it is not involved in trigeminal-mediated headshaking. No abnormalities in the nerve have been found so far in affected horses.
This suggested there was a functional, rather than structural abnormality of the nerve, which means there is potential for developing a treatment which reverses the functional problem.
The condition usually starts to affect adult horses in their prime, with median ages of onset varying from 6 to 10 years. Geldings appear over-represented, comprising 63% to 71.5% of cases. All breeds appear susceptible.
Finding effective treatments is challenging, she says, given that neither the pathology nor cause is known. “It is possible that there is more than one cause with the same clinical manifestation, leading to different response rates to treatment.
“It is recognized in human medicine that response to treatment for neuropathic pain varies among individuals, even with the same diagnosis.
“Therefore, even if all trigeminal-mediated headshakers have the same underlying condition, response
to the same treatment may vary.”
Among scientifically proven methods, the use of a nose net provides some relief in a significant number of causes.
Roberts discussed a number of drugs which have been tried, with varying success. Given that some individuals can respond well, these drugs are worth trying as long as expectations are managed, she says.
“It should be noted that use of these medications would not be allowed in competition, and this fact may be sufficient to limit further research in this area.”
Turning to surgery, she noted that a bilateral infraorbital neurectomy was effective in 3 out of
19 horses, with serious side-effects being common. “However, it was important in that it added to the weight of evidence of involvement of the trigeminal nerve.”
Caudal ablation of the infraorbital nerve (the section of nerve below the eye sockets) via coil compression had better results, with about a 50% success rate in 57 horses, but 26% had relapsed within an average of nine months or so.
“Most horses developed side-effects of nose rubbing which were short-term in most cases, but 4 out of 58 were euthanized due to severity or nonresolution of these side effects.”
She says neuromodulation has been used, which involves electrical nerve stimulation. It is technique that has proved effective for people with nerve-related pain. An initial trial in horses has shown promise and it may be a good first line of treatment for horses who do not respond to a nose net.
Electroacupuncture has also shown promising results in a small group of horses.
Around 93.3% of owners felt their horses improved following homeopathic treatment of varying regimes, as part of a larger study into homeopathy.
Roberts notes that researchers have surveyed owners of headshaking horses to learn about owner-reported diagnoses and outcomes. The owners variously reported the use of antihistamines, antimicrobials, corticosteroids, nonsteroidal anti-inflammatory drugs, melatonin, chiropractic treatment and acupuncture. Based on owner reports, none stood out as more successful than the others.
Roberts says trigeminal-mediated headshaking in horses has both welfare and economic implications.
“Further research is required to fully demonstrate proportions of horses affected worldwide and proportions of horses of each degree of severity.
“There is also an absence of longitudinal data which would reveal whether and how the condition may be expected to progress and in what fashion, as well as the proportion of horses which may be expected to experience spontaneous resolution.
“Without this information, the detailed full scale of the problem to the population is unknown.”
She continues: “Even in the absence of this information, impact on the individual horse and horse owner can be severe, even resulting in the euthanasia of the horse and all that implies to the
“There is no one safe and effective treatment and, even if aiming for management rather than cure, results are variable.”
She says that while advances are being made in understanding the condition and in progressing new treatments, major progress is unlikely until the cause and subsequent development of the condition is fully understood.
“In the meantime, the author recommends a thorough investigation to be as sure as possible of diagnosis, followed by logical trials of published treatments.”
Trigeminal-mediated headshaking in horses: prevalence, impact, and management strategies
Veterinary Medicine: Research and Reports, January 9, 2019, Volume 2019:10 Pages 1—8