Are stereotypies a form of OCD?

A recent study has looked at similarities between equine stereotypical behaviours and human Obsessive-Compulsive and Related Disorders.

Stereotypical behaviours in horses, such as crib-biting, weaving, and box walking, are often misrepresented as “vices”. They are not vices, but rather pathological behaviours caused by the way we keep them. In fact, a recent study by Stephanie Megan Plato at the University of Winchester compares them to human Obessive-Compulsive and Related Disorders (OCD).

There is precedent with regards to categorizing certain behaviours in non-human animals as OCD. Tail chasing in dogs, fur pulling in mice, and fence pacing in polar bears, for example, have previously been classified as OCD. So far, however, no equine stereotypies have made the cut (which is a bit surprising given the analogy between pacing in a captive polar bear and box walking in a stalled horse).

To categorize behaviours in non-human animals as OCD, there need to be certain similaritites with regards to aetiology, neurological mechanisms, presentation, and treatment. The study, Comparing the pathology of equine stereotypical behaviours to obsessive-compulsive and related disorder in humans: An exploratory Delphi study (2022)¹, used a Delphi protocol to facilitate a discussion between five acknowledged experts on equine stereotypies and OCD, in order to get them to agree on a set of similarities and differences.

Below, I’ve summarized the main points of the study, beginning with the similarities.

Similarities between equine stereotypical behaviours and OCD

Background:

• Genetic predisposition.

• Similar neurological dysfunction (altered basal ganglia functions and changes to the cortico-striatal-thalamic circuitry²).

• Coping mechanisms that help the individual deal with stress.

Causes:

• Inadequate environment.

• Inadequate companionship.

Diagnosis:

• Repetitive behaviours without a clear function or goal.

• Prioritized over other behaviours, leading to altered time budgets in the affected individuals.

Prognosis:

• Will not subside without treatment.

Differences between equine stereotypical behaviours and OCD

• Different presentations due to different behavioural biologies.

• Environment plays a more important role in equine stereotypies than in OCD.

• Equine stereotypies have a dietary connection (concentrated feed increases the risk of crib-biting), whereas human OCD doesn’t.

What we don’t know (yet)

• OCD patients suffer from intrusive, obsessive thoughts. Horses have the same neurological pathways (cortico-striatal-thalamic circuitry, see above) that are responsible for obsessive thoughts in humans, but we don’t know whether they experience obsessive thoughts, and if they do, whether they are similar or different to those experienced by humans.

So, what’s the bottom line?

The study concludes that there are some notable similarities between equine stereotypical behaviours and OCD, but not enough to fully categorize stereotypies as OCD. More research is needed, particularly when it comes to the neurological mechanisms and the presence of obsessive thoughts in horses.

From my perspective, the categorization of stereotypies as OCD isn’t nearly as important as educating horse owners about the origin and function of stereotypic behaviours, something the study also touches on. There are still many misconceptions about stereotypies which, to quote the study, can lead to “extreme cruelty” when owners revert to physical prevention and punishment.

Stereotypies are a welfare concern, because they are a sign that the horse is or has been living in stressful conditions. When horses experience pain and/or stress, for example because of hunger, social isolation, or confinement, they revert to certain coping behaviours. These are often “empty” behaviours associated with the type of stress they experience: a horse that wants to move but can’t may start to weave or pace, while a horse that isn’t fed an optimal diet may start to crib-bite.

When a horse performs these behaviours, enorphins are released. They reduce the pain and stress the horse is experiencing, thus negatively reinforcing the behaviours. If the environment isn’t changed, the behaviours will be repeated, eventually becoming stereotypies.

While stereotypical behaviours are often defined as having no function, I argue that the function is, in fact, to alleviate some of the stress caused by the environment. The endorphin release and the fact that stereotypical behaviours become established so quickly imply that they are important coping mechanisms. From this it follows that horses should not be prevented from doing them, as prevention will likely increase their stress levels.

1. Plato, S. M., 2022. Comparing the pathology of equine stereotypical behaviours to obsessive-compulsive and related disorder in humans: an exploratory Delphi study. Applied Animal Behaviour Science ,248. https://doi.org/10.1016/j.applanim.2022.105571

2. One expert disagreed with this and said that CSTC involvement has not been proven in horses.