WHILE the exact cause of headshaking in horses – repeated uncontrolled vertical or horizontal shaking of a horse’s head at rest – is not known, facial pain is believed to be the most common cause.

That’s according to veterinary surgeon Sarah Ross, a 2008 graduate of Liverpool University, who addressed the topic at last week’s 18th Irish Equine Veterinary Conference at the Celbridge Manor Hotel (see 106-107 also).

Headshaking can be non-stop in some horses and the attending delegates heard that possible causes are many and varied – among them, poor riding, bad behaviour, cervical pain, ear mites, back pain and facial pain.

Of this long list, facial pain was said to be among the most common cause with origins in tooth root abscess or trigeminal mediated headshaker, the latter described as the most common.

Young adult horses, in the five to 10-year-old age group, can exhibit headshaking the most and it can be acute (sudden) or insidious.

Ross told the delegates that headshaking can be seasonal in approximately one third of affected horses, occurring more in spring/summer and reportedly worse outdoors or at exercise.

Affected horses may carry their heads very low on the lunge and while being ridden. They can be difficult to bridle and being dangerous or impossible to ride, the condition can lead to euthanasia.

Ross described facial pain as “a welfare issue” and told delegates that the “big recent advance is that the trigeminal nerve is hyper excited in these horses).”

Citing facial pain in people as being associated with a high suicide rate, Ross also revealed that headshaking is a bilateral problem in horses and in the case of six horses in a controlled test environment, nerves from headshaking horses were found to fire at a very low threshold compared to the normal horse group.

“Despite being structurally normal, the nerve is functionally abnormal,” said Ross.

Is it reversible?

A complete history should be documented of affected horses including what signs does the horse exhibit, does it occur at exercise versus rest, is it seasonal?

Does the headshaking occur in the stable or out in the field? If the latter, this rules out behavioural issues.

Owners of such horses were advised to take a video of it occurring to show their veterinary surgeon and provide as much detail about it as possible using the history guidelines above. If it occurs only when being ridden, Ross advised that vets see the horse being ridden.

NERVE BLOCKING

Headshakers are graded zero to three and the veterinary delegates heard that bilateral posterior ethmoidal nerve block is very useful (behind the eye) but it can be tricky for vets to get it in the exact right place.

Ross recommended veterinary delegates perform upper respiratory track endoscopy and if CT is available, then a fracture of the head can even be seen in some cases.

Delegates heard that the application of a cheap nose net can turn off the pain pathways by distracting the pain fibres and can give relief in up to as many as 75% of cases.

Treatments such as TENS and PENS can be useful with positive results from controlled tests at Bristol University.

SURVEY

Sarah Ross carried out an online questionnaire with 1,000 responses covering 932 horses and estimated the prevalence of this condition at 4.6%.

In most causes, the respondents said that 53% of horses showed signs on the lunge, one in five showed headshaking at rest. Less than one third of cases had been seen by a vet. The cause was unknown in the majority of causes. The conference heard that perhaps the lack of veterinary consultation by owners on this issue was that owners tend to see headshaking as a behavioural issue more than a health one. However the findings on facial pain should be noted. Ross said that she believed headshaking could be more prevalent among sport horses but pointed out that thoroughbred horses are usually retired by five to 10 years of age.