( ask the vet ) Headshaking in Horses By Emily Haggett BVSc, DipACVIM, MRCVS
heads for a variety of reasons – for example, in response to pain caused by an ear or sinus infection, colic or arthritis, or as a response to flies, pollen or dust. Repeated and seemingly involuntary headshaking may, however, be indicative of a nerve disorder called trigeminal-mediated headshaking, or ‘trigeminal neuralgia’.
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Headshaking can be very distressing to deal with and can be a significant welfare issue for affected horses, affecting their performance and daily functions and can vary in severity, with symptoms frequently becoming worse over a period of time. The condition can also pose a significant safety hazard to the horse’s handler or rider and needs to be correctly diagnosed by a vet and treated appropriately. This may require referral to a specialist at a veterinary hospital for a range of diagnostic tests. Headshaker cases are complex and require a ‘multidisciplinary’
approach including orthopaedic, neurological, ophthalmological, respiratory, and oral assessment. This can help to give a more accurate diagnosis and eliminate other causes of pain-related responses.
he condition of headshaking has been well described as a syndrome for many years, but it is an area that requires further research to be fully understood. Horses shake their
can make the symptoms worse. What causes Headshaking?
In a small percentage of horses a true ‘physical’ reason exists as the cause of headshaking. Examples of this include an infected tooth root or other dental problem, a cyst or other mass in the sinuses, or pain elsewhere in the horse’s body. For a large proportion of horses with headshaking no physical abnormality can be found and the condition is caused by facial pain caused by trigeminal neuralgia. In this situation, the trigeminal nerve (which is responsible for facial sensation) becomes overactive. The threshold for stimulation of the nerve reduces and the nerve will ‘fire’ excessively causing facial pain. It is still not completely understood what causes the nerve to function abnormally.
Many horses who headshake display clinical signs only during spring or summer, when pollen can be one of the trigger factors.
What are the clinical signs?
There are a number of variable signs of headshaking but clinical signs can include:
• Up/down or side to side shaking or twitching of the head - this can vary from mild to severe
• Ear and eyelid flicks • Snorting or high-blowing • Nostril clamping (closing) • Face rubbing - a common sign that probably relates to areas of pain or numbness, possibly linked to severely damaged parts of the nerve
• Sweating • An anxious facial expression • Distracted behaviour, such as striking at the muzzle during exercise, stopping and rearing
These behaviours can occur at different times but are oſten worse when the horse is exercised. In some horses distinct ‘triggers’ such as bright sunlight, high pollen counts, wind or rain
18 SUMMER SPECIAL 2019
CT imaging is useful for evaluating teeth or sinus problems Seasonality
In a large number of cases, headshakers show the signs only at a particular time of year, most commonly during the spring and summer months. Trigger factors can include pollen, bright sunlight, insects, dust, warmth, cold, rain or wind.
Treatment options
Treatment can be challenging. Specific treatments may be indicated for horses in which a physical problem is identified. These will depend upon the results of the investigations but may involve joint medication, dental/sinus surgery, or medical treatment of allergies and lower airway disease.
Trigeminal neuralgia can be difficult to manage. Avoiding or reducing exposure to trigger factors is oſten the best way of
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