# Headshaking

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{{short description|Horse behaviour}}
'''Headshaking''' is a behaviour displayed by [horses](/source/Horse), where the horse continuously shakes its head vertically and/or horizontally.<ref name=":0">{{Cite journal|last=Roberts|first=Veronica|date=Jan 9, 2019|title=Trigeminal-mediated headshaking in horses: prevalence, impact, and management strategies|journal=Veterinary Medicine: Research and Reports|volume=10|pages=1–8|pmc=6330979|pmid=30666296|doi=10.2147/VMRR.S163805 |doi-access=free }}</ref> In the 1980s it was considered a bad behaviour, but instead it turned out to be a painful medical condition.<ref>{{Cite web|url=https://www.horseandhound.co.uk/horse-care/vet-advice/headshaking-in-horses-89386|title=Headshaking in horses: Horse & Hound veterinary library|date=2019-11-13|website=Horse & Hound|language=en-US|access-date=2019-12-02}}</ref>

Minor head tossing is quite common in most horses as a response to insects and airborne irritants, however headshaking is a separate, severe issue.<ref name=":1">{{Cite book|title=Equine Behavioral Medicine|last=Beaver|first=Bonnie V.|publisher=Elsevier Inc.|year=2019|isbn=978-0-12-812106-1|location=London, UK|pages=311–345}}</ref> The headshaking needs veterinary attention if it occurs spontaneously with no sign of any external stimuli that may cause the motion.<ref name=":2">{{Cite book|title=Equine Medicine, Surgery and Reproduction|last=Lane|first=J. Geoffrey|publisher=Elsevier Ltd.|year=2012|isbn=978-0-7020-2801-4|location=Edinburgh, UK|pages=77–109|edition=Second}}</ref> The behaviour is most commonly described as a vertical flicking of the head, as if an insect has flown up the animal's nostrils.<ref name=":8">{{Cite journal|last=Crabbe|first=Barb|date=January 2018|title=The facts of headshaking|journal=Horse & Rider|volume=57|pages=54–56, 58|id={{ProQuest|1980700610}}}}</ref> Many horses also show nasal irritation and engage in rubbing or striking the muzzle off of stationary objects, such as walls and fences.<ref name=":1" />
thumb|275x275px|A horse displaying headshaking
The behaviour is most commonly displayed while the horse is being led, [lunged](/source/Longeing), or ridden, and typically subsides while the horse is at rest.<ref name=":3">{{Cite book|title=Equine Sports Medicine and Surgery|last1=Carr|first1=Elizabeth A.|last2=Maher|first2=Omar|publisher=Elsevier Ltd.|year=2014|isbn=978-0-7020-4771-8|location=Edinburgh, UK|pages=503–526|edition=Second}}</ref> This makes riding a horse with the syndrome dangerous, as they may begin to violently toss their heads and thus, throw off the rider's balance.<ref name=":1" /> Because of its prevalence during exercise, many riders incorrectly attribute headshaking to a behavioural problem or to poorly fitted [tack](/source/Horse_tack).<ref name=":3" />

Although other causes have been noted, the most common cause of headshaking is the [neurological disorder](/source/neurological_disorder) known as trigeminal neuralgia.<ref name=":3" /> It has been found that many factors, such as environment, sex, and breed, contribute to the prevalence of the behaviour.<ref name=":1" /> Many treatments have been proposed to help control the symptoms of the condition, but a solution to cure the behaviour has yet to be found.<ref name=":6">{{Cite journal|last=Roberts|first=Veronica|date=May 2018|title=Managing headshaking in horses: An update|journal=In Practice|volume=40|issue=4|pages=157–161|doi=10.1136/inp.k1493|s2cid=79847134|id={{ProQuest|2210117315}}}}</ref>

== Causes ==
thumb|230x230px|Equine facial nerves
Headshaking may be caused by a variety of medical issues, such as [ear ticks](/source/Tick) or [mites](/source/Mites_of_domestic_animals), dental diseases, airway abnormalities, skull trauma, sinusitis, etc.<ref name=":1" /> However, the most common and well-researched cause is trigeminal neuralgia, a neurological condition that affects the animal's [trigeminal nerve](/source/trigeminal_nerve) and results in abnormal firing.<ref name=":0" /> The [somatosensory- evoked potential](/source/Somatosensory_evoked_potential) was tested and is in healthy horses established at 10mA, while affected horses show a result of 5mA. Research shows that the infraorbital nerve branch of affected horses is sensitized and has an increased threshold compared with unaffected horses.<ref name=":0" /> The branch, therefore, has a lower firing threshold and can be triggered by various, even minor stimuli.<ref name=":4">{{Cite book|title=Equine Internal Medicine|last1=Aleman|first1=Monica|last2=Nout-Lomas|first2=Yvette S.|last3=Reed|first3=Stephen M.|publisher=Elsevier Inc.|year=2018|isbn=978-0-323-44329-6|location=Missouri, USA|pages=580–708|edition=Fourth}}</ref> But some seasonally affected horses seemed to have a normal threshold, when tested out of season. If the clinical symptoms are in fact connected to the threshold of the nerve, it holds the possibility of a reversible condition.<ref name=":0" /> 

The maxillary branch of the trigeminal nerve plays a major role in facial sensation, thus causing the horse to feel intense pain in the face and muzzle area.<ref name=":3" /> It was distinguished that there is no difference in the involvement of the left or right branch from the trigeminal nerve.<ref name=":0" /> The horse's pain is expressed in its obsessive headshaking and evasive behaviour.<ref name=":6" /> The condition is known as "trigeminal-mediated headshaking" or "facial pain syndrome".<ref name=":3" />  
{| class="wikitable"
|+Potential non-neurological causes of headshaking<ref name=":4" />
!Oral cavity disorders
!Eye disorders
!Ear disorders
!Airway disorders
!Skull disorders
!Cervical pain
!Other
|-
|Dental disorders
|Vision abnormalities
|[Otitis](/source/Otitis)
|[Rhinitis](/source/Rhinitis)
|Fractures or trauma
|[Osteoarthritis](/source/Osteoarthritis)
|Avoidance behaviour
|-
|Buccal ulceration
|[Cysts](/source/Cyst), masses, [cataracts](/source/Cataract)
|[Ear mites](/source/Ear_mite) or [ticks](/source/Ticks_of_domestic_animals)
|[Guttural pouch](/source/Guttural_pouch) disease
|[Temporomandibular joint](/source/Temporomandibular_joint) disorders
|[Neuropathy](/source/Peripheral_neuropathy)
|[Stereotypy behaviour](/source/Stereotypy_(non-human))
|-
|Pharyngeal lesions
|[Nasolacrimal duct](/source/Nasolacrimal_duct) disorders
|Masses, [abscesses](/source/Abscess), [granuloma](/source/granuloma)
|Laryngeal disorders
|[Hyoid apparatus](/source/Hyoid_apparatus) disorders
|[Myositis](/source/Myositis)
|Ill-fitting tack
|-
|Tongue lesions
|
|
|[Sinusitis](/source/Sinusitis)
|
|
|Rider behaviour
|}<br />

== Diagnostic ==

The veterinarian has to observe the horse during exercise, at rest and under the influence of different environments and possible triggers.<ref name=":0" /> It sometimes can be helpful to have video materials of the owner and observe the horse on different days, to distinguish certain triggers. 

After the inspection, the horse has to be examined for other causes of the headshaking not related to the trigeminal- nerve.<ref name=":9">{{Cite web|url=http://www.newmarketequinehospital.com/headshaking-in-horses/|title=Headshaking in horses|date=2018-04-19|website=Newmarket Equine Hospital|language=en-GB|access-date=2019-12-02}}</ref> 

Additional diagnostics should be considered as well. These include:<ref name=":9" /> 

* MRI 
* X-Rays 
* CT
* Endoscopy

Even though there can be a variety of different causes, 98% of the affected horses in need of veterinary care turned out to have no connection to external causes, leading to a connection to the trigeminal-nerve.<ref name=":0" /> 
== Influences on prevalence ==

=== Environmental triggers ===
Research has shown that trigeminal-mediated headshaking may be triggered by various external factors, such as temperature, season, time of day, wind, light, and many others. Approximately 1.4% of horses are affected by headshaking and of those with the condition, 64% are affected seasonally.<ref name=":1" /> Light availability seems to play the biggest role in triggering the behaviour.<ref name=":1" /> Affected horses tend to experience more symptoms when outdoors on sunny days.<ref name=":1" /> Therefore, headshaking occurs most often during the spring and summer months when sunlight is more prevalent.<ref name=":1" /> This side of the syndrome is termed "photic headshaking" and is thought to occur due to the close proximity of the optic and trigeminal nerves.<ref name=":3" /> The symptoms of photic headshakers lessen when indoors and during the nighttime.<ref name=":4" />

Headshaking appears to occur in horses all over the globe, but variations in the symptoms can be based on region.<ref name=":5">{{Cite journal|last1=Pickles|first1=Kirstie|last2=Madigan|first2=John|last3=Aleman|first3=Monica|date=July 2014|title=Idiopathic headshaking: Is it still idiopathic?|journal=The Veterinary Journal|volume=201|issue=1|pages=21–30|doi=10.1016/j.tvjl.2014.03.031|pmid=24821361}}</ref> In the USA, 91% of affected horses were found to experience increased headshaking during the spring and early summer.<ref name=":5" /> While in the UK, only 39% of affected horses displayed worsened symptoms during only the spring and summer months, with more horses being affected during the spring, summer and fall.<ref name=":5" />

Other individuals have been found to be triggered by the wind conditions, rain conditions, and the presence of loud sounds, although the reasoning behind these influences are currently unknown.<ref name=":5" />

=== Age and sex ===
Headshaking seems to be an acquired condition that develops during the prime of the horse's life.<ref name=":0" /> It affects a wide age range, but the majority of horses develop the behaviour after reaching maturity, usually between 6-10 years old.<ref name=":0" /> A larger percentage of [geldings](/source/Gelding) appear to be affected by the condition  when compared to [mares](/source/Mare) and [stallions](/source/Stallion).<ref>{{Cite journal|last1=Madigan|first1=John E.|last2=Bell|first2=Stephanie A.|date=Aug 1, 2001|title=Owner survey of headshaking in horses|journal= Journal of the American Veterinary Medical Association|volume=219|issue=3|pages=334–337|doi=10.2460/javma.2001.219.334|pmid=11497047|doi-access=free}}</ref> In some studies, as high as 90% of headshakers were found to be geldings.<ref name=":5" /> It is thought that geldings may be more susceptible to headshaking, as they do not have testosterone feedback, therefore during the spring when horses typically mate, the gelding's [gonadotropins](/source/Gonadotropin) will be incredibly heightened.<ref name=":5" /> The gonadotropins alter the sensitivity of the trigeminal nerve, making it unstable and more susceptible to stimuli.<ref name=":5" />

=== Exercise ===
Exercise can also influence the intensity of headshaking behaviour. Intense or more frequent exercise provides more stimulation to the brain causing increased firing of the trigeminal nerve.<ref name=":5" /> The increased airflow over the muzzle and nostrils while riding or lunging may also play a factor.<ref name=":3" />

=== Breed and discipline ===
thumb|237x237px|A horse and rider performing dressage
Headshaking has been observed in a wide variety of horses and is thought to be able to occur in any breed.<ref name=":0" /> Some studies show that the behaviour is more common in [Thoroughbreds](/source/Thoroughbred) and [Warmbloods](/source/Warmblood), however this point is refuted by other researchers who argue that headshaking is equally likely to be seen in any breed.<ref name=":4" />

When it comes to discipline, headshaking horses are typically found to be [pleasure riding](/source/pleasure_riding) or general all-purpose riding horses.<ref name=":5" /> Other disciplines that restrict the movement of the horse, such as [dressage](/source/dressage) or [eventing](/source/eventing), also tend to have more cases of headshaking.<ref name=":2" /> Intense, high activity disciplines like [racing](/source/Horse_racing) and [showjumping](/source/Show_jumping), show a decreased amount of affected horses.<ref name=":2" />

== Impact ==
Headshaking is a condition which impacts the life and the welfare of affected horses.<ref name=":1" /> Since the behaviour is caused by facial pain, the horse may be in constant discomfort.<ref name=":0" /> The intensity of the behaviour can range and therefore, some horses may experience greater pain than others. Various scales have been created and used to rank the intensity of headshaking behaviour.<ref name=":0" />
{| class="wikitable"
|+Roberts headshaking behaviour grading system<ref name=":0" />
!Scale
!Description
|-
|0
|No headshaking behaviour
|-
|1
|Mild headshaking behaviour, insufficient enough to not interfere with riding
|-
|2
|Headshaking behaviour severe enough to make riding dangerous or impossible
|-
|3
|Headshaking behaviour occurs even at rest
|}
Humans who suffer from [neuropathic facial pain](/source/Trigeminal_neuralgia) describe their symptoms as anything varying from tingling sensations to feelings similar to intense electric shocks.<ref name=":0" /> [Translational research](/source/Translational_research) may be possible to infer similarities in pain between affected humans and horses.<ref name=":6" /> It is thought that the horses feel sensations of tingling, itching, burning and electric-like shocks.<ref name=":7">{{Cite journal|last=Madigan|first=John|date=October 2000|title=Therapy for headshaking|journal=Journal of Equine Veterinary Science|volume=20|issue=10|pages=630|doi=10.1016/S0737-0806(00)80416-5}}</ref> They attempt to alleviate this pain by throwing and tossing their heads, as well as rubbing the nose, snorting and sneezing.<ref name=":7" /> This behaviour can cause the horse to become dangerous to ride, or even handle on a daily basis.<ref name=":7" /> The condition can also become an economic burden on the owner, as depending on the method, the treatment may be costly to keep up with.<ref name=":0" />

== Treatment ==
Various treatment methods have been proposed to lessen the effects of headshaking, however, the behaviour has yet to completely cured.<ref name=":4" /> The success of a technique may vary depending on the horse's particular characteristics.

=== Nose nets ===
Nose nets may cover the horse's entire muzzle (nostrils and lips) or only the nostrils.<ref name=":5" /> The net prevents irritants from entering the nostrils, decreases the amount of stimuli affecting the horse's muzzle area and may provide a constant [counter-stimulation](/source/Counterstimulation) to the nerves of the face.<ref name=":5" /> This method is noninvasive, cheap and is also permitted to be worn in most equestrian competitions.<ref name=":0" /> It is one of the most successful treatment methods, although it does not eradicate the problem completely.<ref name=":0" /> Approximately 70% of owners who attempted this method reported at least somewhat of an improvement in the symptoms of their horse.<ref name=":5" /> It appears to be more effective if used immediately after diagnosis, as older horses who have lived with the condition for longer, were found to be less likely to show any improvement.<ref name=":5" />

=== Face masks ===
thumb|249x249px|A horse wearing a face mask
Face masks can be successful in reducing the symptoms of photic headshakers. Usually the mask contains ultraviolet shades to block out any sunlight.<ref name=":5" /> This method works to reduce the stimulation affecting the ophthalmic branch, thus reducing the stimulation of the trigeminal nerve.<ref name=":6" />

=== Eye drops ===
[Sodium cromoglycate](/source/Cromoglicic_acid) eye drops are used to stabilize [mast cell](/source/mast_cell) membranes and has been effective in a limited number of seasonally affected horses.<ref name=":0" /> It is thought that eye drops may only work as a treatment for horses who experience headshaking as a result of environmental allergies.<ref name=":5" />

=== Surgery ===
Infraorbital [neurectomy](/source/neurectomy), in which the trigeminal nerve is cut or blocked, has been used to attempt to treat headshaking.<ref name=":5" /> This method is not used anymore, as the rate of success was quite low and the surgery had serious side-effects on the horse.<ref name=":0" /> More recently, compression of the caudal infraorbital nerve via platinum coils has been attempted as a last option treatment, although the rate of success is only 50% and the chance of injury post-surgery is quite high.<ref name=":5" />

=== Medication ===
A wide variety of pharmaceuticals have been used in trials attempting to reduce headshaking in horses. Many may have adverse side-effects and may also be banned from use in show horses.<ref name=":5" /> [Cyproheptadine](/source/Cyproheptadine) is an [antihistamine](/source/antihistamine) and [serotonin antagonist](/source/Serotonin_receptor_antagonist) which has been effective in significantly reducing headshaking symptoms in many horses.<ref name=":0" /> It can be used alone or in conjunction with [carbamazepine](/source/carbamazepine), an [anticonvulsant](/source/anticonvulsant) used to treat nerve pain in humans.<ref name=":8" /> Other past and presently used forms of medication include: [Gabapentin](/source/Gabapentin), [dexamethasone](/source/dexamethasone), [fluphenazine](/source/fluphenazine), and [phenobarbitone](/source/Phenobarbital).<ref name=":6" />

=== Supplements ===
[Magnesium](/source/Magnesium) supplemented into the diet of affected horses has shown some successful reduction of headshaking behaviour, especially when combined with [boron](/source/boron).<ref>{{Cite journal|last1=Sheldon|first1=Shara A.|last2=Aleman|first2=Monica|last3=Costa|first3=Lais R.R.|last4=Weich|first4=Kalie|last5=Howey|first5=Quinn|date=May 2019|title=Effects of magnesium with or without boron on headshaking behavior in horses with trigeminal‐mediated headshaking|journal=Journal of Veterinary Internal Medicine|volume=33|issue=3|pages=1464–1472|doi=10.1111/jvim.15499|pmid=30990929|pmc=6524471|id={{ProQuest|2247641608}}}}</ref> It is thought that magnesium may have calming effects on the over-sensitive nature of the trigeminal nerve.<ref name=":8" /> However, magnesium supplementation can be dangerous, as high doses need to be used to create an effect.<ref name=":5" /> [Melatonin](/source/Melatonin) has also been used as a treatment for horses suffering from photic headshaking.<ref name=":8" /> It works to alter the horse's internal clock and shows the best results when administered at the same time every night, so that its effects will kick in during the day.<ref name=":5" /> Many researchers argue that the effects of feed supplements are mere [placebo effects](/source/Placebo) and do not actually help with the symptoms of the condition.<ref name=":0" />

Percutaneous electrical Nervous stimulation (PENS) is used as a treatment for human patients with trigeminal facial nerve pain. It was tested on horses recently and could turn out to be a working treatment, more research on this method is necessary.<ref>{{Cite journal|last1=Roberts|first1=V. L. H.|last2=Patel|first2=N. K.|last3=Tremaine|first3=W. H.|date=2016|title=Neuromodulation using percutaneous electrical nerve stimulation for the management of trigeminal-mediated headshaking: A safe procedure resulting in medium-term remission in five of seven horses|journal=Equine Veterinary Journal|language=en|volume=48|issue=2|pages=201–204|doi=10.1111/evj.12394|pmid=25475743|issn=2042-3306}}</ref> 

== References ==
{{Reflist}}
Category:Horse behavior

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Adapted from the Wikipedia article [Headshaking](https://en.wikipedia.org/wiki/Headshaking) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Headshaking?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.