Head-shaking has long confused and frustrated horse owners, leading some to euthanize their mounts.

In the past, a horse that regularly displayed violent up and down motion of the head, often along with excessive snorting or sneezing, under saddle and at rest, with no identifiable cause, was labelled an idiopathic (unknown cause) head-shaker.

These days, the term idiopathic head-shaking has been replaced with trigeminal-mediated head-shaking. Researchers now believe it is related to hypersensitivity of the trigeminal nerve in the head. A recent study by British researchers from the Animal Health Trust highlights the importance of being able to tell the difference between head-tossing behaviour related to musculoskeletal pain and trigeminal-mediated head-shaking.

After studying six horses referred for investigation of “head-shaking” – including review of case histories and video footage, plus physical assessments at work and at rest – the researchers were able to identify musculoskeletal issues as potential causes of head-tossing in all of the animals.

They reported that all six of the horses showed head-tossing behaviour when ridden, and two also tossed their heads on the lunge. In five of the horses, dramatic improvement was seen when the causes of the lameness – including poor saddle fit – were addressed. In the sixth horse, head-tossing was eliminated on the lunge, but not completely resolved when ridden or at rest. This led them to believe there was some element of trigeminal-mediated head-shaking behaviour involved.

The team says these results show how important it is for vets to recognize pain-related behaviours, like head-tossing, and be able to separate them from trigeminal-mediated head-shaking to avoid misdiagnosing horses.