Headshaking in horses may also be referred to as equine headshaking syndrome, idiopathic headshaking or trigeminal-mediated headshaking. It is characterised by abnormal jerky movements of the horses head, usually in an upward/downward motion. This is often accompanied by lip movements, a desire to rub their nose, snorting and general agitation.
In many cases headshaking can make a horse unrideable (symptoms are usually much worse during work) and is considered to be the result of pain, so it is important that the condition is addressed.
Causes of Headshaking in Horses
There are many possible causes of headshaking-type behaviour including dental problems, traumatic nerve damage (from an accident for example), ill-fitting tack, sinusitis, eye disease or ear mite infestation. But normally when we talk about headshaking we are referring to idiopathic headshaking, a condition which may affect as much as 6% of the UK equine population to some degree and around 2% notably.
Idiopathic Headshaking In Horses
Idiopathic is a general term used to refer to a disease which occurs spontaneously and without known cause. In other words, idiopathic headshaking is headshaking that cannot be attributed to a cause such as those listed above. Onset most often occurs between six and nine years of age, it is slightly more common in geldings but is not associated with particular breeds.
Around 60% of cases appear in spring and summer, often disappearing altogether over autumn and winter, giving rise to the term seasonal headshaking. Many of these horses will worsen with time, their headshaking becoming more pronounced and persisting for longer each year.
Idiopathic headshaking has been subject to considerable study in recent years and is now more accurately termed trigeminal mediated headshaking.
Triggers (as distinct from causes) for trigeminal headshaking can be anything that stimulates the facial nerves and includes touch, light (photic headshaking) and even sound. Although pollen is still commonly associated with headshaking, trigeminal headshaking is no longer considered to be the result of allergy.
Trigeminal Mediated Headshaking
We can now attribute the vast majority of cases of idiopathic headshaking to neuropathic pain of the trigeminal nerve (trigeminal mediated headshaking). Neuropathic pain simply describes pain from sensory nerves caused by stimuli that would not ordinarily be painful.
The trigeminal nerve transmits sensory information from the face to the brain. It comprises of three major branches, the ophthalmic nerve (the eye), the maxillary nerve (mid-face including the nose, cheeks and upper lip) and the mandibular nerve (the jaw).
Headshaking has been attributed to sensitisation of the trigeminal nerve. Scientific research (focusing on the maxillary portion) has demonstrated a reduced threshold for activation in horses that headshake. This means that a much lower stimulus is needed to illicit a pain response. This is why a normal stimulus, such as light, can cause shocks of pain.
Unfortunately we still have no explanation for why this hyper sensitisation may occur.
Neuropathic pain is a well-documented condition in humans but common causal factors do not tally with headshaking in horses. Herpes viruses have been considered (as with shingles) but ruled out.
The most similar human condition to headshaking is trigeminal neuralgia, a condition also characterised by hypersensitisation of the trigeminal nerve. But this occurs when the nerve loses its protective coating, this does not seem to be the case with headshaking.
It is likely that the cause of headshaking is multifactorial, with genetic, physiological and environmental factors all contributing (making it very difficult to study).
Treatment of Trigeminal Headshaking in Horses
Headshaking is a painful condition meaning that you should seek advice from your vet if your horse is showing notable symptoms.
The inability to use prescription medication in competition means that it is rarely a viable option for most horse owners. Neuropathic pain is also known to be quite resistant to pain medication and sometimes, when there is improvement, it is short-lived. Similarly, medication for allergy seems to have very limited benefit. There are also side-effects to consider. None the less, some horses will benefit more than others, so you should discuss available options with your vet.
Surgical intervention for trigeminal headshaking involves the physical compression of the nerve by the insertion of a small platinum coil. However, as well as being invasive and expensive, surgery is only thought to be effective in around 50% of cases, many revert back within the first nine months.
Many vets now offer PENS (percutaneous electrical stimulation) therapy as a less invasive measure for headshaking. This is similar to TENS except that rather than being transcutaneous (over the skin), the electrodes are inserted percutaneously (under the skin). The aim is to try and reprogram the nerves, although the scientific mechanism is not understood. PENS is thought to improve headshaking in around 50% of cases but benefits are short term (anything from 2days to 5months).
Management of Headshaking Horses
The difficulties of treating trigeminal headshaking mean that effective management is always important.
Take note of triggers and avoid them wherever possible. This may mean not riding when the pollen count is high or in the brightest part of the day, and turning out overnight. Triggers can be different for each horse, so consider your horse individually. Other triggers include dappled light (moving through trees for example), wind, rain or midges.
Horses are usually worse in work, so you may need to limit the intensity of their exercise. Also consider your horses’ tack as it may create discomfort. Remember that physically restricting your horse from headshaking will not address the pain and may increase distress.
Using a nose net is one of the simplest things you can try. Effective for around 25% of headshakers, a nose net is safe, economical and often allowable in competition (check with your association). Owner reports do suggest a much higher efficacy, but these are likely to be overstated due to the subjective nature of owner feedback. It is thought that a nose net works by providing a constant, non-painful stimulus that helps to normalise the nerve communication.
As a general safeguard for good health, ensure a good diet with the full spectrum of vitamins and minerals. Magnesium, in particular, is known as an essential nutrient that plays an important role in nerve conduction, so you should ensure an ample dietary supply. Be aware that there are many supplements marketed toward the allergy concept of headshaking, these are unlikely to help your horse but probably will have a placebo effect on you!
Try to be objective in how you asses your horse, taking note of scale and frequency. This will help you to identify patterns, track your horse’s progress year on year and will help you to give your vet reliable feedback. A problem with headshaking research has been unreliable reporting from owners.
At present, there is no unified grading system for headshaking. Vets often use a simple three scale approach (mild - difficult to ride – headshaking at rest and impossible to ride) but more detail will help you to monitor your horse. You may find the following descriptions useful.