Headshaking is a pain, metaphorically and literally. There can be nothing more frustrating than being able to neither ride your otherwise healthy horse nor understand why. Many owners spend years worrying about the state of their tack or their own riding ability in an attempt to explain this bizarre and potentially dangerous behaviour. However, many equine scientists now believe that headshaking is the result of a pain in the nose.
What is headshaking?
Excessive headshaking is usually only apparent when the horse is ridden or exercised, especially after warming up. However, severe headshakers may still show signs when grazing in the field. Most noticeable is the twitching or shaking movements of the head, which may be vertical, horizontal or rotary. Most headshakers show other signs of irritation of the head area and may rub their noses along the ground, on fence posts or the riders leg. They may try to strike their nose with their foreleg, clamp their nostrils shut, snort excessively or twitch their top lip. Progressive exercise or stress seems to exacerbate these behaviours and can lead to a manic, uncontrollable animal. Headshaking is commonly a seasonal problem, beginning in the spring, worsening over the summer and disappearing by the autumn. But there are always exceptions, some which were seasonal now headshake all year round and a few actually start in the autumn.
Headshaking is a presenting sign (a symptom) of over 60 diseases in the horse, including ear, respiratory and neurological disorders. Unfortunately, in the vast majority of cases, no other sign of disease can be found that would explain the behaviour and the horse is labelled an idiopathic headshaker- of unknown cause.
What causes it?
At the moment it seems that every case is different and most owners find that no amount of dietary, tack or management changes make the slightest bit of difference. Some researchers have suggested that this is because idiopathic headshakers are suffering from a form of human trigeminal neuralgia (Tic douloureux). Branches of the trigeminal nerve supply sensation to the nose, face and mouth and neuralgia in these may result in shooting pains within the nose. The head-snatching is an involuntary reaction to this and the rubbing is an attempt to remove the unpleasant sensation. The horse may be affected bilaterally (on both sides of the face) or unilaterally, with the head movements moving towards the affected side. Researchers are not sure why certain horses may have this neuralgia. As yet unconfirmed theories include; previous trauma to the muzzle area resulting in damaged nerves, hypersensitivity reactions to some vaccinations or neuralgia caused by the bit pressing on the sensitive tissues of the mouth.
Certain situations may make the nerve more sensitive and spark off a bout of headshaking. Common triggers seem to be exercise, wind, heat and sunlight. These elements can exacerbate the problem in the human form of neuralgia so it is likely that the same is happening here. Many owners feel their horse is allergic to a range of allergens in the countryside including pollen from crops, grasses and trees in the spring and summer, and moulds or dust throughout the year. But due to the lack of success of conventional treatments for allergies, the idea that the majority of headshakers have hayfever per se is losing interest within the veterinary community. It maybe more likely that it is a variety of triggers acting together that causes the reaction. For example, the culmination of exercise, sunlight and the stress caused by swarming flies (i.e. a typical hack!) can have the effect of triggering the neuralgia.
Getting a diagnosis
Whilst it may be fairly easy to get your vet to agree that your horse has a headshaking problem, it is still very hard to find the exact cause of the problem. Nerve blocks may be successful and can be used to make a diagnosis of neuralgia, but as a treatment, severing the nerves surgically is not without its problems nor failures. Luckily Liverpool Vet School has been having success with some new drugs.
A variety of tests such as riding indoors or with a sun-blocking facemask on may help eliminate sunlight as a trigger. Likewise, a mask over the muzzle may suggest that wind or air borne allergens are a factor. Lungeing in just a head collar may eliminate the bit as a cause but, unfortunately, if the neuralgia has been present for a long time or is particularly severe it is likely that some of these tests will be inconclusive. Work at De Montfort University is focusing on how we can use tests like these to form a reliable diagnosis. We have already shown that headshaking occurs in all breeds and ages of horses and that type of use, diet and other management factors are unlikely to be reliably related to the cause of headshaking.
Whatever the reason your horse headshakes, it is unlikely that he has a simple behaviour problem. Once the source of the pain has been removed the headshaking usually stops.
What can I do?
Any owner that has acquired a headshaker (or suspects they have) or has a headshaker whose symptoms have improved and are willing to help by completing a questionnaire or by participating in field trials of treatments, such as masks and bridles, should contact Katy Taylor at Dept of Medical Statistics, De Montfort University, Leicester LE1 9BH or email email@example.com or visit the website: http://www.medstats.dmu.ac.uk/headshaking