Nodding away flies and giving the odd head bob is normal horse behaviour, but full-blown headshaking in horses could mean something rather more serious is going on. In this article, an equine vet explores its causes and management, a clinical animal behaviourist explains post-inhibitory headshaking and a leading researcher helps three owners whose horses headshake.

Your horse is uncontrollably and involuntarily shaking his head in a violent fashion, jerking it up and down while also snorting and sometimes rubbing his muzzle. They seem distressed. They are a headshaker, and while the number of affected horses is low, those who do suffer with this distressing condition may also (less commonly) shake their head horizontally or rotationally in a movement that’s neither behavioural nor stereotypical in nature and which shouldn’t be confused with head tossing.

Causes of headshaking in horses

According to vet Leona Bramall MRCVS, many questions about headshaking remain unanswered, and research into it is ongoing. It’s thought that headshaking results from trigeminal nerve pain (known as trigeminal-mediated headshaking/trigeminal neuralgia) which frequently involves the branch of the trigeminal nerve supplying the nasal cavity.

Occasionally a physical cause of the pain is identified but, more often than not, the precise cause of the pain cannot be found, meaning that the vast majority of cases are termed ‘idiopathic’ (cause unknown). A trigger factor generally precipitates headshaking in horses and can include certain climatic conditions (bright lights, warmth, cold, wind, rain and so on), environmental allergens, insects, and other possibilities.

Headshaking often has a seasonal link, with clinical signs starting in the spring and getting worse over the summer before abating in the winter. In some horses, though, clinical signs aren’t season-dependent. Other horses may only headshake intermittently, or under certain conditions.

How to manage headshaking in horses

Sadly, idiopathic (unknown) headshaking in horses isn’t curable, but a number of treatments may be tried in the hope of reducing the problem. Many of these are unproven and lack sound scientific evidence, so take care if you decide to use them and seek advice from your vet.

Nose nets, UV masks and ear covers may help, either individually or in combination. Equine-specific contact lenses can be used in cases where corneal sensitivity is considered a trigger factor. Horses who show a positive response to topical, local anaesthetic eye drops gain the most benefit from contact lenses.

Your vet may also recommend an intranasal inhaler, especially if endoscopy has indicated inflammation of the nasal passages or upper respiratory tract. Oral antihistamines, steroids or non-steroidal anti-inflammatory medications (NSAIDs) can have varying degrees of success. Other drug options include carbamazepine and cyproheptadine, though results are variable and often short lived.

Recent scientific research suggests that EquiPENS (Percutaneous electrical stimulation) neuromodulation is showing promise as a minimally invasive procedure. The procedure involves placing a probe directly over the nerve and stimulating it for a set period. Current research indicates that 50% of horses treated have benefited.

Caudal compression of the infraorbital nerve can also improve clinical signs in more than 50% of cases. However, reoccurrences and post-operative complications may occur.

Behavioural headshaking in horses

Some horses habitually twist and shake their heads at certain times when ridden, for example after jumping a fence. They may be displaying post-inhibitory headshaking, as Debbie Busby, clinical animal behaviourist, explains.

“Some of the motivations for headshaking can be impatience, anxiety, pain or pathological disorder. A vet check for a physical or neurological issue is always advisable,” Debbie explains. “Post-inhibitory headshaking is a type of behavioural rebound. This is in the context of behavioural or ethological needs that are specific to individual species and necessary for maintaining their optimal wellbeing.

“Think about what happens when stabled horses are turned out in an arena or paddock. Often, they will run around for a few minutes first, because their species-specific need to move around – including trotting and cantering – was prevented for a number of hours.

“These rebound behaviours indicate that stabled horses become frustrated by the inability to perform their species-specific movement behaviours through exercise.”

Such headshaking in horses can also occur if a horse is held together on a strong contact or tight rein during jump schooling, often the only time the rider decreases or even loses contact is on the landing or away phase of negotiating a fence. Sometimes it might also be displayed by a buck or change of rhythm.

Debbie suggests the following ways to minimise behavioural headshaking in horses:

  • Loose school, lunge or long-rein before riding. If time is tight, increase turnout time instead, including turnout before riding – perhaps while you do other jobs. All of these activities afford opportunities for the horse to express species-specific behaviours and thus reduce the likelihood of rebound.
  • During schooling sessions, take regular, frequent breaks on a loose rein.
  • Warm up with a relaxing hack before schooling.

Headshaking in horses: real life case studies

Dr Veronica Roberts, an RCVS specialist in equine internal medicine and senior lecturer at the University of Bristol Vet School, helps three owners whose horses headshake.

The problem: hair loss

My mare experiences hair loss on her face in spring and summer, can be snotty and is a seasonal headshaker. Could these things be connected? What medical management strategies could be tried?

Dr Veronica answers: I’m sorry to hear that, it certainly sounds difficult to manage. The first step is to see whether the headshaking and the hair loss and snotty nose are connected. There is a complex — and not yet understood — association between environment and trigeminal-mediated headshaking, but it isn’t a ‘normal’ allergy.

With the hair loss, work out whether the itch or the hair loss comes first. Does she become itchy after the hair falls out, or is it coming out because she’s itching and rubbing? Is she rubbing due to discomfort from trigeminal-mediated headshaking triggers, or are they separate things? Does hair loss/itch start before or after her seasonal headshaking signs return? Working out these things will be helpful to your vet.

When she has a snotty nose, have an endoscopy carried out and take a sample to see if she has asthma. These things can be connected. If she does, discuss treating it with steroids with your vet, if appropriate for her. This will allow you to see which of her problems resolve with this treatment, which might help you work out any association. Steroids are a more effective treatment for any allergy in horses than antihistamines, as their immune system works a bit differently to ours.

The problem: pesky bugs, rain and group riding

My thoroughbred mare is a headshaker, but only when ridden in three specific situations: when there are flies or midges; in light rain; when she isn’t in front of a group hack when trotting or cantering. Could she be getting cross, as there isn’t always a physical trigger, or is she experiencing something?

Dr Veronica answers: Trigeminal-mediated headshakers appear to be suffering neuropathic pain in response to stimulation of their trigeminal nerve, which is the main sensory nerve to the face. Horses with this condition have a trigeminal nerve that is about 10 times more sensitive than normal.

This seems to cause neuropathic pain — people who suffer from this describe as varying from pins and needles, bearable to unbearable burning, and bursts of electric shock-like pain. It is this pain and altered sensation that makes horses throw their heads.

The increased sensitivity means some horses will experience pain when exposed to anything that stimulates the nerve, such as flies or rain, and whether they are ridden or not. I advise seeing if the mare does it on the lunge, or on a lead or long-reins if safe, or if it’s only when on a ride. Trigeminal-mediated headshaking becomes a more likely diagnosis if she does do it when exercised but not ridden.

If she isn’t affected at rest by the presence of flies, then it doesn’t rule out either anxiety or trigeminal-mediated headshaking, as trigeminal-mediated headshakers are more likely to suffer pain at exercise than at rest. When she’s doing it behind the others, think about whether she is in the firing line for dust or particles kicked up by them, or even wind disturbance, which could stimulate the nerve, or whether this is just her way of expressing anxiety.

The problem: considering PENS treatment

How extreme would headshaking need to be for a horse to be considered for PENS treatment?

Dr Veronica answers: EquiPENS™ is minimally invasive and low risk. It works through inserting a small electrode into the trigeminal nerve while the horse is under sedation, with the aim of returning the nerve to its ‘normal’ state and function.

The RCVS published a study on its use in 168 horses (530 procedures) in the UK and Europe. It is suitable for any properly diagnosed trigeminal-mediated headshaker who either doesn’t respond at all or sufficiently to use of a nose net, or where a nose net isn’t suitable (they are not allowed for all competition types and levels).

We expect half of horses to go into remission – where they are able to perform ridden work at their previous level – but only 18% are cured. The others will need repeat procedures when they start headshaking again. The majority of these will go back into remission again and for longer, but there are a small number of horses which do cease to respond. Where horses do not respond to treatment, we have to consider their welfare and quality of life.

Some horses only experience the pain at exercise and can be retired, but this isn’t always an option for the owner or even the horse. Others will be affected even at rest and, for them, they would be in pain even in retirement. This does mean that, sadly, some trigeminal-mediated headshakers do have to be euthanised.

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