Headshaking Syndrome

CHAPTER 23 Headshaking Syndrome

The term headshaking describes both a syndrome that includes many other behaviors and a specific behavior within this collection. Not all horses that are reported by their owners to shake their head or to be headshakers necessarily have a medical problem involving the head, and it must first be established that the behavior observed in a given horse is not an expression of normal behavior. Shaking the head is a natural behavior in horses and is typically seen as a manifestation of facial irritation, such as from flies, or an expression of frustration, as might arise when the horse is being held back at a race or separated from other horses or food. Head nodding describes a repetitive up-and-down movement of the head and commonly occurs in two contexts. First, in the housed horse, head nodding is often seen in response to locomotor frustration, as in a horse restrained by a barrier, such as the stable door, which prevents access to things the horse wants, including other horses. Like weaving, head nodding is reduced by increased social contact (see Chapter 24, Management of Stereotypic Behavior [Stable Vices]). Second, in exercised horses, head nodding arises with lameness and is often most evident at the trot.


Owners typically present horses with a headshaking problem in spring, summer, or fall with recurrent, intermittent, sudden, and apparently involuntary bouts of head tossing that may be so extreme as to throw the horse and rider off balance. For this reason, headshakers can be dangerous to ride, and owners commonly report an inability to train or compete effectively on them. With such horses, sneezing or snorting, nasal discharge, and attempts to rub the nose on the ground, a forelimb, or other nearby objects frequently accompany the headshaking. Other common behaviors include clamping the nostrils as if to close them, wriggling or flipping the top lip, and engaging in protective behaviors to avoid contact between human handlers and the head (Table 23-1). Horses in the stages of a headshaking attack may be best described as acting as though an insect has flown up their nostril. Video footage of the behavior should be considered an essential prerequisite to assessment and is relatively simple to obtain.

Table 23-1 Reported Causes of Headshaking

Diseases of the nasal cavity Allergic or vasomotor rhinitis
Nasal sinus tumors
Trombicula autumnalis (harvest mite) infestation
Diseases of the ear Psoroptes spp. mites in the ear canal
Otitis media or interna
Diseases of the eye Melanotic iris cysts
Diseases of the nervous system Equine protozoal myeloencephalitis
Cervical spinal injury or other cause of cervical instability (e.g., subclinical wobbler syndrome)
Trigeminal neuralgia (many causes)
Glossopharyngeal neuralgia
Diseases of the skeletal system Maxillary osteoma
Temporohyoid osteoarthropathy, with or without associated cranial nerve damage
Premaxillary bone cyst
Periapical dental abscess
Diseases of the soft tissues of the head Parotid gland melanomas
Guttural pouch mycosis
Irritation from poorly fitting tack

Readers are referred to Mills DS, Taylor KD, Cooper JJ: Weaving, headshaking, cribbing, and other stereotypies. In Proceedings. Annual Convention of the American Association of Equine Practitioners 51:221-230, 2005. Available on-line at http://www.ivis.org/proceedings/aaep/2005/mills/chapter.asp?LA=1.for a more extensive list of putative causes.

Although the condition can occur at rest, headshaking is more obvious during exercise in most horses, especially at the trot and after a brief warmup period. The prevalence of headshaking remains unknown, but it seems to be increasingly common and has been reported in Europe, North America, and Australasia. The problem may start at any age, but the median age of onset is approximately 5 years. An association is often made with ridden exercise or regular work, but this may be coincidental.

Headshaking has been reported in both sexes and various breeds, including warmbloods, ponies, and crossbreds. It has been suggested that Thoroughbreds may be at particular risk, despite the fact that the condition is uncommon in racehorses, possibly because of their age or the nature of the discipline. The high representation of Thoroughbreds described in reports may be a reflection of their high value. It has also been suggested that geldings are overrepresented, but castrated males are also more common in the general working population, so this, too, may be a misleading assumption. The problem has been reported in horses of various disciplines and levels of sporting achievement, although horses used for dressage may be at increased risk. This may be a response to the bit or of the tension and flexion of the neck in dressage work. Alternatively, dressage riders may be more sensitive to the horse’s head movements because mild cases of head nodding could impact scoring in this sport, which requires stillness in head and body carriage.

Approximately 60% of headshakers appear to be affected only during the spring and summer months; the remaining horses are typically affected year round, either intermittently or persistently. In the latter group of horses, the condition may initially have been seasonal and the severity of headshaking may continue to worsen during the warmer months. Given the seasonal pattern of onset, many associations have been made, by owners and in the literature, between the season and the condition with little solid supporting evidence. The condition’s seasonality has been explained by the effects of increased exercise, heat, bright sunlight, and changes in air quality (such as the presence of irritants and allergens). In the United States, none of these trigger factors has been reported to reliably elicit the problem except exercise and exposure to ultraviolet (UV) light. In the United Kingdom, even ultraviolet light does not appear to consistently induce headshaking in horses known to have the condition. Increased workload during the spring and summer seems an unlikely explanation for the seasonality of the problem, and it is more likely that headshaking is more common in those months because of an accumulation of risk factors rather than because of any single factor.

Diagnosis is often complicated by the intermittent nature of the problem, which can result in absence of the behavior at the time of examination, especially if the horse was moved to a different location. This underscores the value of obtaining video footage of the problem. In determining the potential causes and treatment of an affected horse, the veterinarian should not overlook the intermittent nature of the problem.


The intermittent and apparently involuntary nature of headshaking, together with the presence of other behaviors (see Table 23-1), suggests that headshaking is frequently a response to nasofacial irritation or pain, but it is important to appreciate that there is no single cause of headshaking and owners must be prepared for a potentially lengthy diagnostic process that ultimately reveals little. Case reports in the veterinary literature suggest that a number of disease syndromes can be associated with headshaking.

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May 28, 2016 | Posted by in EQUINE MEDICINE | Comments Off on Headshaking Syndrome

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