The problem with pain

Recognizing when a horse is in pain can be a difficult task. Here's why.

Everyone is talking about pain right now. Given the recent scandals that have exposed violent training methods and abusive equipment in horse sport, this comes as no surprise. Yet the discussion often over-simplifies a hugely complex topic.

There is a lot of misunderstanding around pain and pain-related behaviours in horses, so I will try to unpack some of the complexity. I want to warn you before you read any further: this is a long post. I have split it into the following sub-headings so you can read it in chunks:

• What is pain?

• What does pain in horses look like?

• How can we tell if a horse is in pain?

• Can we tell if a horse is not in pain?

• The bottom line

But before we dive in, let’s start with an example from the real world.

A few days ago, one of my horses had a choke episode. It was immediately obvious to me that something was wrong. I had just brought them in for the night, and normally they go into their stables and settle down to eat. But after a short while, my horse came back out, walked around the yard with his head low to the ground, and then parked himself outside my pony’s stable.

My horse during his choke episode last week. You can see his uneven stance and the contracted neck.

This was a clear change in his normal behaviour in this context, and my first red flag that something was wrong. As he stood there, I noticed some other behaviours that also did not fit his normal behavioural repertoire:

• uneven stance

• sometimes extending one of his front legs in front of him

• lifting and contracting his neck upwards-backwards

• stretching and moving his jaw around

• unresponsive to the environment

• clear ‘pain face’ (more on what a ‘pain face’ is further down)

My horse showing a clear ‘pain face’ - tension around the jaw and muzzle, tension around the eyes (‘worry wrinkle’), lowered ears pointing backwards, flared nostrils.

At this point I was confident that something was wrong (and suspecting choke), so I called the vet. While I was on the phone to the clinic, he regurgitated a large batch of feed and saliva, confirming that it was indeed a choke episode (I have this on video but will spare you the sight), and then went back into his stable.

I knew he was not well yet, because he was:

• standing tucked away in a corner

• not showing any interest in his feed

• still showing a clear pain face

Withdrawing to the back of his stable and facing a corner - note also the uneven stance and the slightly lifted tail.

Fortunately, while I was still on the phone to the vet, the choke resolved on its own, and after a bit of hand walking and hand grazing he was back to normal. But the whole progression of behaviours makes an interesting example of how pain can manifest behaviourally in a real-life situation.

That was the anecdote. Now let’s dive into the science.

What is pain?

Pain science is a vast field of multidisciplinary research in which I am not an expert, so this section will only provide a top-level explanation of the main considerations.

Essentially, pain has two components: a physiological response and a subjective experience. The International Association for the Study of Pain defines it as ‘an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage’¹.

For the purpose of this post, the key takeaways are that pain 1. is unpleasant, 2. has an emotional component, and 3. does not have to involve actual tissue damage.

The sensation of pain is called nociception, and it involves specific nerve endings that respond to pressure, temperature, or chemicals and send electric impulses to the spinal cord (for reflexive action) and to the brain (for perception and action).

The experience of pain is subjective and affected by things such as stress and emotional state. This means that even seemingly ‘small’ injuries can cause an individual to experience a high level of pain and associated emotions.

What, then, is the difference between ‘pain’ and ‘discomfort’? None that matters.

This is a huge pet peeve of mine. ‘Discomfort’ is often used to diminish or dismiss a horse’s experience of pain, and in my opinion, trying to assign degrees of severity to someone else’s experience is nothing but an exercise in futile anthropocentrism.

For the purpose of dealing with pain in our horses, we need to understand that pain is an unpleasant sensation that involves negative emotions and that there doesn’t have to be a correlation between the severity of damage and the intensity of the experience.

It is not up to us to decide what our horses are feeling, or how strongly. If a horse tells us they are in pain, they are in pain, and that’s all we need to know.

So how can a horse tell us that they are in pain?

What does pain in horses look like?

There has been considerable research into the behavioural markers of pain in the last decade or so. In 2021, Torcivia and McDonnell published the Equine Discomfort Ethogram (EDE) based on decades of clinical research into equine pain behaviours².

The EDE describes 64 behaviours associated with pain and/or discomfort. (The paper is open access and has video links for each behaviour, so you can see what they look like in real life.)

My horse displayed a number of behaviours from the EDE during his choke episode, for example stretching, camping under, withdrawing (called ‘guarding’ in the ethogram), atypical jaw movement, raised tail, and a depressed demeanour.

An example of a behaviour in the Equine Discomfort Ethogram, screenshot from Torcivia and McDonnell (2021).

In 2018, Dyson et al. published The Ridden Horse Pain Ethogram (RHPE), a list of 24 behaviours that may indicate the presence of musculoskeletal pain in a ridden horse³. According to the researchers, if a horse exhibits 8 or more of these behaviours within the same 5-minute period, that should be taken as indication of a potential problem. The RHPE has been applied in a number of follow-up studies since, and there are many online resources available that describe how to use it.

The Ridden Horse Pain Ethogram, screenshot from Dyson et al. (2018).

The attentive reader will notice quite a few similarities between the EDE and the RHPE. This overlap makes perfect sense given that both describe pain-related behaviours. The EDE is a more general and comprehensive pain ethogram, whereas the RHPE is a diagnostic tool for a specific type of pain under ridden conditions.

In addition to the ethograms, we also have the Horse Grimace Scale by Dalla Costa et al. (2014)⁴ and the Equine Pain Face by Gleerup et al. (2015)⁵. My apologies to the two research teams for saying what I am about to say, but they essentially describe the same thing in different words: a specific facial expression associated with pain.

The components of this ‘pain face’ are present in a number of species - including humans - and involve tightening of the areas around the eyes and nostrils, clenching of the jaw, and lowering the ears and pointing them backwards (in species that have mobile ears).

An illustration of the Equine Pain Face (b and c), screenshot from Gleerup et al. (2015). You can compare the illustration with the photo of my horse further up.

How can we tell if a horse is in pain?

In December 2022, I was interviewed by Horse Network about a video of Karl Cook’s horse Kalinka which had garnered some criticism online. Most of the criticism centred around the fact that Kalinka’s behaviour was indicative of pain.

Here’s what I said in that interview: “Professionally, I would not be able to look at this video and say this horse is in pain. I would also not be able to look this video and say this horse is not in pain because there’s just not enough information.”

So what would be ‘enough information’ to determine if a horse is in pain? Well, as with all behaviour, it’s complex. Let’s start with the caveats.

First of all, if you look at the behaviours in the pain ethograms, it is clear that many of them may be displayed in situations not necessarily associated with pain. Examples of such behaviours are the ‘frustration head toss’, ‘bucking’, ‘rolling’, ‘tail swishing’ and ‘pawing’.

This illustrates how important context is to the interpretation of behaviour. Behaviour is often ambiguous, and we need to consider the whole situation. For example, a swatting tail may be completely normal insect-repelling behaviour in a summer field, but stand out as odd in the middle of winter.

Another important consideration when observing pain-related behaviours in horses is that they generally don’t like to show them. Prey species have evolved to mask overt signs of illness or disability, because predators quickly learn to watch out for such tell-tale signs of an easy meal.

In fact, a 2020 study by Torcivia and McDonnell, where they recorded pain-related behaviours in equine patients in a clinical setting through 24-hour video surveillance, found that they decreased by a mean of 77.4% as soon as a person appeared. And 30% of horses stopped showing any signs of pain whatsoever!

Interestingly, Gleerup et al. noted in the Equine Pain Face study a (statistically not significant) increase in human-directed contact-seeking in the horses in their study. This increased contact-seeking may contribute to masking some of the pain-related behaviours and facial expressions.

Another important caveat is that pain and stress are closely linked. Lundblad et al. (2021) found that pain-free horses display facial expressions similar to the ‘pain face’ when exposed to mildly stressful situations⁶. As pain leads to a physiological and emotional stress response, it can be hard to disentangle whether a behaviour or facial expression is due to pain or ‘just’ stress.

There are also the usual personality aspects to consider: different individuals will show pain in different ways. A horse with a more active coping style might engage in more overt behaviours, while a horse with a more passive coping style might be more likely to ‘shut down’ and show very subtle signs. As with everything, it pays to know your own horses and what is ‘normal’ vs. ‘abnormal’ for them.

So, what can we do to evaluate whether a horse is in pain?

This will depend on whether we are looking for signs of injury or illness in our own horses, or signs of painful equipment and handling in other people’s horses. Most of us are concerned with taking good care of our own horses, so the suggestions below are geared towards daily management of familiar horses rather than assessing the effect of handling techinques.

Rather than looking for specific behaviours, I often find that a change in behaviour is the strongest indicator that something is wrong, particularly if the change is sudden or very pronounced. As in the example with my horse, when a horse does something it normally wouldn’t do in a particular situation, that is a red flag. Paying close attention to changes, particularly if they involve behaviours from the pain ethograms or a ‘pain face’, is important.

In a recent webinar for World Horse Welfare⁷, Equine Clinical Animal Behaviourist Gemma Pearson said that one of the clearest indicators of pain for her is a horse not progressing in its training. I think this is worth keeping in mind for those horses who are in consistent training - a ‘plateau’ may be an indication that something is wrong.

Another thing to pay attention to is the number and frequency of the pain-related behaviours. A sudden buck may indicate a horse fly bite - painful, yes, but not something that needs veterinary attention. But several pain-indicating behaviours displayed synchronously and/or consistently over a period of time is a red flag.

And finally, in my experience, aggression is a major red flag, particularly for chronic pain. Under natural conditions, horses rarely engage in overt aggression, so increased aggression levels are always a sign that something is wrong.

To sum up, the main things to look out for when assessing the presence of pain are:

• changes in behaviour or facial expression, particularly if they are sudden and/or involve behaviours from the pain ethograms

• ‘plateaus’ in training (both from the ground and under saddle)

• repeated pain-related behaviours over a period of time

• increased levels of aggression against other horses or people

However - and this is really important! - given that most signs of pain in our horses will be very subtle and hard to spot, I strongly argue in favour of erring on the side of caution when suspecting pain - because once we notice it, it’s probably quite bad.

Furthermore, in most cases the main risk is confusing pain-related behaviours with stress-related behaviours. As stress is also associated with a negative emotional experience, there is never any disadvantage to taking signs of stress seriously, too.

Can we tell if a horse isn’t in pain?

The short answer to this is: no. Not reliably, anyway.

This is because of three reasons:

1. The nature of pain.

2. The nature of horses.

3. The nature of our relationship with horses.

First of all, pain is a subjective experience. It is not necessarily associated with any underlying tissue damage. This means that lack of injury or illness does not equal lack of pain, and that we can never reliably know if another individual is experiencing pain unless they tell us.

This leads us to the nature of horses. They cannot speak; the only way they can communicate that they are in pain is through their behaviour and facial expressions. Unfortunately, they have evolved to hide pain to a great extent, and combined with the fact that we are generally lousy at reading our horses, it makes spotting when they are in pain very difficult.

Additionally, there will be individual variations in how horses express pain. For example, research into orthopedic pain in horses found low-to-moderate association between pain-related facial expressions and degree of lameness, with considerable individual variation - and some lame horses showed no ‘pain face’ at all!⁸

Finally, the way we use horses gives them ample opportunities to experience pain, but few opportunities to express it.

Most common riding aids work through the targeted application of pain. In textbooks, this is often called ‘pressure’, which is a euphemism for pain, because in order for a horse to learn from the ‘release of pressure’, the pressure needs to be unpleasant in the first place. (More progressive and scientifically savvy trainers admit that pressure-release training requires ‘discomfort’, but I’ve already explained why I don’t like that term.)

On top of this, much of the equipment we use (leveraged bits, nosebands, draw reins, martingales etc.) is designed to restrict horses’ ability to communicate, which includes pain- and stress-related behaviours. As a secondary consequence, they often cause pain either through direct mechanical pressure or through soreness from being forced to move in a restricted, static position.

One example: a horse opens its mouth to get relief from painful bit pressure⁹. What do we do in response? We tighten the noseband even harder. Now the horse stops showing the pain-related behaviour ‘opening the mouth’. Does it mean it is no longer experiencing pain?

Additionally, our reliance on using punishment to deal with unwanted behaviours means we risk punishing a lot of pain-related communication, too. Scroll back up and take a look at the behaviours in the Ridden Horse Pain Ethogram. How many of these behaviours have you heard some online guru say are due to ‘disrespect’, followed by a suggestion to ‘correct’ the horse for showing them?

One example: your horse rears because of pain in his back. You crack an egg on his skull when he does to ‘discourage’ the ‘vice’. (This is a real method! Please don’t do this to your horses.) He finds it so frightening and unpleasant that he stops rearing under saddle. Is his back no longer painful?

While many of the ethograms and diagnostic tools for behavioural pain assessment in horses are great, I want to be very clear on this point: while they can help diagnose the presence of pain, they cannot be used to rule out pain.

The bottom line

Thanks for reading this far! I hope it was worthwhile, and that I have managed to get across at least some of the complexity and nuance of pain from a behavioural perspective.

The 5 key things I hope you take away from this post are:

• Pain is a subjective experience.

• Individuals will experience and express pain differently.

• Pain and stress are closely linked, and often manifest in similar behaviours.

• It is important to consider context when evaluating pain-related behaviours.

• Never assume that a lack of pain-related behaviours is the same as alack of pain.

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All opinions expressed here are my own.

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1. https://www.iasp-pain.org/publications/iasp-news/iasp-announces-revised-definition-of-pain/

2. Torcivia C, McDonnell S. 2021. Equine Discomfort Ethogram. Animals 11: 580.

3. Dyson S, Berger J, Ellis AD, Mullard J. 2018. Development of an ethogram for a pain scoring system in ridden horses and its application to determine the presence of musculoskeletal pain. Journal of Veterinary Behavior 23: 47-57.

4. Dalla Costa E, Minero M, Lebelt D, Stucke D, Canali E, Leach MC. 2014. Development of the Horse Grimace Scale (HGS) as a pain assessment tool in horses undergoing routine castration. PLoS One 9(3): e92281.

5. Gleerup B, Forkman B, Lindegaard C, Andersen PH. 2015. An equine pain face. Veterinary Anaesthesia and Analgesia 42(1): 103-114.

6. Lundblad J, Rashid M, Rhodin M, Haubro Andersen P. 2021. Effect of transportation and social isolation on facial expressions of healthy horses. PLoS ONE 16(6): e0241532.

7. Training horses: where to begin? Webinar by World Horse Welfare, 29 November 2023.

8. Ask, K. 2022. The look of lameness - Behaviors and facial expressions associated with orthopedic pain in horses. Doctoral thesis, Swedish University of Agricultural Sciences.

9. Eisersiö M, Yngvesson J, Hartmann E, Egenvall A. 2023. Gaping for relief? Rein tension at onset and end of oral behaviors and head movements in unridden horses. Journal of Veterinary Behavior 59: 8.14.