Head-shaking: Study points to musculoskeletal pain as a cause

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The importance of eliminating musculoskeletal pain as a potential cause of head-shaking in horses has been highlighted in a British study.

Researchers reported a dramatic resolution of head-shaking behaviour in five of the six horses at the centre of the study after resolving their musculoskeletal problems.

Katy Thompson, Cheryl Chan and Sue Dyson, from the Animal Health Trust, set out to report on the clinical findings of six horses referred for investigation of head-shaking.

The case records of the horses were studied and video footage was examined where available.

A comprehensive clinical examination at rest and exercise, including a ridden assessment, was performed on each horse several times over at least two days. Diagnostic analgesia was used and imaging was carried out.

The researchers, writing in the journal Equine Veterinary Education, reported that all the horses showed head-tossing behaviour when ridden, and two horses also tossed their heads on the lunge.

All were found to have various sources of musculoskeletal pain, based upon on-the-ground assessments by Dyson, a specialist in equine orthopaedics, and the other diagnostic work carried out.

Most horses had more than one source of pain contributing to lameness.

When poor saddle-fit was corrected (two of the horses had ill-fitting saddles with tight tree points) and pain causing lameness was eliminated using diagnostic analgesia, there was a dramatic resolution of head tossing behaviour under all circumstances in five of the horses.

In the sixth horse, head tossing was eliminated on the lunge but not completely resolved when ridden.  This horse also displayed clinical signs at rest and it is likely that there was an element of trigeminal-mediated head-shaking — a condition relating to hypersensitivity of the trigeminal nerve in the head.

The condition, formerly known as idiopathic head-shaking, can be distressing to both the horse and its caregiver. Severe cases can result in euthanasia. It is often diagnosed based on the exclusion of all other potential causes.

The authors noted that many horses with trigeminal-mediated head-shaking showed clinical signs both at rest and when ridden, often worsening when ridden.

However, all horses in the study showed additional signs of musculoskeletal pain when ridden compared with in-hand and on the lunge, the trio noted.

“None of these horses displayed excessive sneezing or snorting, acting like an insect was flying up the nostril and rubbing and/or striking at the nose with the forelimbs which can often be seen in horses with trigeminal-mediated head-shaking.”

None had a history of seasonality of clinical signs, which can be another indicator of the nerve-related condition.

The study team says it is important for vets to recognise behaviours that suggest pain, such as head-tossing during riding, and to be able to separate this behaviour from trigeminal-mediated head-shaking, which research has shown affects between 1% and 4.6% of British horses.

The researchers acknowledge that nerve-related head-shaking is very hard to diagnose because of the nonspecific and unreliable nature of available diagnostic tests.

“Therefore, emphasis must be put on using the characteristic history and clinical signs and a thorough, logical, step-wise investigation to rule out any other potential cause.”

Their case series, they said, highlighted the importance of ruling out all possible causes of repeated abnormal head movement before diagnosing trigeminal-mediated headshaking.

It is entirely possible, they added, that some horses are mistakenly diagnosed with trigeminal-mediated head-shaking when in reality the horse is tossing its head because of orthopaedic pain.

“It has been shown that horse-owners and trainers are rather poor at recognising low-grade lameness and as a result, a high proportion of horses in normal work are lame,” they said.

“It is, therefore, unsurprising that the horses in the current case report had not been identified as lame and instead, the behaviour was classified as classical head-shaking.”

Trigeminal-mediated head-shaking often has a seasonal pattern, a link with sunlight or certain weather conditions, or excessive sneezing or snorting, which none of the horses in the study showed.

“This case series offers an alternative explanation for violent head tossing behaviour.

“Although trigeminal-mediated head-shaking often worsens with exercise, head tossing behaviour which is present only during ridden exercise, and not on the lunge, is likely to reflect musculoskeletal pain,” they wrote.

It is different to trigeminal-mediated head-shaking, which is likely to also be present at rest, associated with weather and seasonality and shows other specific signs.

Head tossing behaviour in six horses: Trigeminal-mediated head-shaking or musculoskeletal pain?
K Thomson, C. Chan and S. Dyson
Equine Veterinary Education, https://doi.org/10.1111/eve.13084

The abstract can be read here.

 

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