Decoding the Headshaking Study

When respected equine scientists publish a study that could revolutionize our understanding of a perplexing condition, we at Curious Equestrian prick up our ears.

Dr. Kirstie Pickles and her team have done just that with their recent paper on using accelerometers to quantify headshaking in horses. Let's dive into this research that's making waves in equine neurology.

Understanding Trigeminal-Mediated Headshaking (TGMHS)

Before we dive into the study's findings, let's clarify what we're dealing with:

TGMHS is an idiopathic facial pain condition in horses. Here's what you need to know:

1. Root Cause: It's believed to be caused by a sensitisation of the trigeminal nerve, leading to a lowered threshold for activation. This results in neuropathic pain - essentially, the horse experiences pain sensations without any actual tissue damage.

2. Symptoms: Affected horses exhibit a range of behaviours, including:

   • Violent head flicks (predominantly vertical, but can be horizontal or rotatory)

   • Signs of nasal irritation (muzzle rubbing, snorting)

   • Striking at the face with a forelimb

3. Severity: The intensity and frequency of these behaviours can vary significantly. In severe cases, horses may headshake even at rest, potentially compromising their welfare to the point where euthanasia might be considered.

4. Prevalence: TGMHS affects approximately 1% of the UK equine population severely enough to require veterinary intervention.

5. Impact: TGMHS can significantly affect a horse's quality of life and performance capabilities. It can make riding unsafe or impossible, leading to career-ending consequences for sport horses.

6. Diagnosis Challenges: Currently, diagnosis is made through careful observation and exclusion of other causes, often requiring advanced imaging like computed tomography of the head.

7. Treatment Difficulties: TGMHS has a poor prognosis, with current treatments lacking consistent efficacy. This makes objective measurement of treatment outcomes crucial for improving horse welfare.

The Study in a Nutshell

Researchers led by Dr Kirstie Pickles used a triaxial accelerometer—think of it as a Fitbit for horses—attached to the poll to measure head movements. Their goal? To differentiate between regular head movements and those associated with TGMHS.

The Science

Here's where it gets interesting:

1. Sample Size: The study included 56 horses—18 with TGMHS, 10 with non-TGMHS, 12 with forelimb lameness, and 16 controls.

2. Methodology: Horses trotted on a lunge for 5 minutes while the accelerometer collected data at a whopping 800 Hz. That's 800 measurements per second!

3. Data Analysis: They looked at various metrics, including the number of head movements, their intensity (measured in g-force), and the ratio of upward to downward movements.

The Findings: More Than Meets the Eye

TGMHS horses shake their heads more violently and frequently. This probably doesn't come as a surprise, but dig deeper, and you'll find some intriguing nuggets:

1. Quantifiable Differences: Compared to other horses, TGMHS horses had over twice as many positive peaks per minute and 12 times more peaks above 2g.

2. Discrimination Power: The study found that specific metrics, like the percentage of peaks above 2g, could excellently discriminate TGMHS horses from others.

3. Non-TGMHS Insights: Interestingly, the accelerometer could also differentiate between TGMHS and non-TGMHS horses, something that's visually challenging even for experienced vets.

Opening New Doors: The Questions This Research Inspires

We're intreagued by the questions this study prompts us to ask:

• While the accelerometer provides quantitative data, experienced horse owners and vets can often spot TGMHS. So, does this technology truly add value to the diagnostic process?

• The researchers suggest this tool could pick up early signs of TGMHS before they're visually apparent. If true, could this be a game-changer for early intervention, and how might it alter our approach to managing horses at risk?

• How might objective measurement of headshaking frequency and intensity standardise our assessment of treatment efficacy over time? Could it lead to more personalised treatment plans?

• How could this method standardise measurements across studies, and what impact might this have on the comparability and reliability of TGMHS research outcomes?

The Limitations:

Every study has its limitations, and we must acknowledge them:

1. Sample Size: With only 56 horses, we need to be cautious about generalising these results.

2. Controlled Environment: The study was conducted during a 5-minute lunging session. How would results differ in varied real-world conditions?

3. Potential for Overdiagnosis: Could this lead to labelling normal variations in equine behaviour as pathological?

Our Take

Quantifying what has previously only been observed opens up new possibilities. Further study and practical application in varied real-world conditions will reveal its true value in time.

Dr Kirstie Pickles, Dr David Marlin, Professor Jane Williams, and Dr Veronica Roberts are highly-esteemed equine experts who make up the team at Animalweb – an independent, unbiased information resource for all animal enthusiasts, and a source of science-based research. 

You can read the full paper here:

Use of a poll‐mounted accelerometer for quantification and characterisation of equine trigeminal‐mediated headshaking (wiley.com)

We want to hear from you, curious equestrians. Here's our poll question:

Share your experiences and opinions in the comments.