Pain – Let’s talk about it

I dedicate this blog to Hege Kristin Dahlbäck and her „healing hands“.

We, who love horses, would probably all agree that pain is a nasty, often a sad topic, yet it is of utter importance. We would all like to protect our four-legged friends from pain and we intend to make any effort to ease their pain as good as we can. However, the silent suffering from pain in horses is often difficult to recognize for us humans. As prey and flight animals, horses try to hide their pain as good as they can. This is quite different from humans, who tend to be so much more openly expressive about feelings of pain. And here comes the next challenge for us humans: Horses, similar to other prey animals do not have a pain sound. This distinguishes horses from other animals who may live in a more or less symbiotic relationship with humans such as dogs and cats. It is so much easyer for us humans to identify pain in these four-legged companion animals, because as „fellow“ predators, they are so much more similar to us!

What can make the situation for a horse in pain even more difficult is the fact that the experience of pain will always have behavioral consequences. Thus, we who care for our horses do not only need to recognize the often hidden and less obvious signs of pain, moreover, we also need to understand the behavioural consequences of pain. A horse who bucks or shows other forms of unwanted or dangerous behavior may not be a „nasty“ horse, in many cases chances are, that this unwanted behavior is an expression of pain. Nonetheless, to have the behavioral consequences of pain in mind may actually be helpful in order to pick up the subtle signs of pain horses as flight animals exhibit. Let‘s take a broad approach in our understanding of pain because it may help to identify pain issues in our four-legged companions before they progress beyond help.

It is legitimate and useful to study a phenomenon across species in order to gain deeper knowledge and to better understand it. Therefore, I would like to first investigate the phenomenon of pain in a species, that we are supposed to know well, the human. Most of us humans know what pain is. I guess, almost all of us have exerienced pain at some point in time in their life. Interestingly, even though everybody knows what pain is, pain is in fact not so easy to define in scientific terms. Everyone would probably agree upon, that pain is a necessary and important signal from the body that something is wrong. However, how about chronic pain states, where the origin of the pain is difficult to determine and the acute warning function of pain is not so easy to identify? Even though our understanding of pain as a complex and multifacetted phenomenon has definitely increased over the last decades, what causes pain and in particular, what it is that causes chronification of pain states is still not fully understood.

We would probably all agree that pain is quite unpleasant, that it can be terrible, and that it is often accompanied by intense emotions. The International Association for the Study of Pain (IASP) defines pain as "an unpleasant sensory or emotional experience that is associated with or resembles actual or potential tissue damage" (Raja et al., 2020; https://www.iasp-pain.org/resources/terminology/, 11.3.23). 

What I find interesting in this definition is the acknowledgement of emotions in this context. In humans, pain is always associated with negative emotions such as fear, anxiety, as well as depression. This has to do with the evolutionary co-development of emotions and pain and how the experience of pain is subsequently hardwired in the brain. With regard to humans, this fundamental entanglement of the pain experience with feelings of fear and helplessness/depression goes so far, that very sad and sometimes traumatic experiences such as the loss of a beloved person are expressed in terms of pain „ … it hurts so bad…. It breaks my heart“. Thus, in humans, depression may in fact express itself through pain, while likewise a pain state may lead to fear, withdrawal, and depression.

Why should that be so? Well, the principal function of a pain is to warn the individual, that something is wrong, that tissue is injured, and that it is important to attend to the problem. An injured animal is at risk to be the victim of a predator and may not survive. Thus, if an injured animal has the possibility to hide because e.g. it lives in a burrow, it will show a withdrawal response and stays hidden as long as it is not fully recovered and functional. Biologically and evolutionay, this „withdrawal/depression“ response makes a lot of sense and is very useful as it helps the individual to survive. Thus, what do we humans do, when we are in pain? We stay at home, we may stay in bed with a migrane, and even if we are for some reason forced to go out, we sure wished we could have stayed at home…

Let’s have a closer look at the options our four-legged companions the horses have. Horses are flight animals and confronted with a threat, they are very likely to choose the flight part of the fight-flight stress response. Only when there is no other option, a horse will resume to fight. A stallion may fight, for the defense of his herd, against a predator or another stallion, nonetheless, horses in general are prone to run.

What happenes to a horse in pain, possibly lame? Horses as flight animals have the ability to hide pain to an almost unimaginable (for us) extend. It is simply a matter of survival as any potential predator will try to identify the weakest individual of the herd and will go for that herd member! As flight animals out in the open field the only chance for survival a predator attack is to run as fast as possible. Now imagine, a horse in pain: He will most likely have the lowest threshold of all his herd members to show a flight reaction in response to a threat! A horse in pain will be extra vigilant and watch out for predators because to be the fastest herd member off is his only chance to survive! Nonetheless, when there are no other options a horse may resume to fight. What would a horse in pain do under an ill-fitting saddle? He will probably buck and bolt as he does not have other means to communicate his pain (remember, no pain sound!).

And there is one (of possibly many) more aspect to the challenge of a horse in pain: We, as humans, will seek a safe place when we are in pain. Most often (hopefully) this will be our home. Now consider the horse: Where is his home? It is the herd, it is his friends, his family. A horse in pain seeking nothing but a safe place will always try to stay with his herd. Because only the herd will give the extra protection a horse in pain needs. For us the human handler this desire may show itself as separation anxiety. Admittetly, separation anxiety can occur without a pain issue, however, a pain issue will in any case increase the risk for separation anxiety substantially.

 A bucking horse, a horse who tends to bolt, a horse who turns uncontrollably and runs back to his herd is admittetly a dangerous horse. These horses are the typical „problem horses“ and they are often judged as being „nasty“ and dangerous. However, after all we have considered up to now, it may just be a desperate horse bereaved of any other possibility to cope and to communicate his pain!

What can we as humans do? Probably the most important thing is to not label the horse as beeing a „bad“ horse. Rather, to be open for the possibility that something is just not right or even terribly wrong. This holds especially true for a horse, that shows an unexpected change of behaviour. As mentioned before, what makes the identification of pain in horses difficult ist the fact, that all prey, but flight animals in particular, will hide pain and discomfort to the absolutely largest extend possible. In horses, this goes even so far that horses show pain or discomfort behavior when alone but stop it as soon as a human caregiver is present (Torcivia & McDonnell, 2021).

Over the last decade, the interest in the horses’ well-being beyond aspects of husbandry have substantially increased and considerable efforts have been made to help people working in the equestrian industry, but also us, the normal “horse lovers” and equestrians, to identify pain in horses. Most of these scientific publications are “open access” which means, everybody can access them through the internet and read them. Thus, my intention with todays’ blog is to raise awareness and make these resources available to all the good horse people out there, who would like to learn how to recognize pain in their four-legged friends.

The first paper I would like to recommend is written by Catherine Torcivia and Sue McDonnell from the University of Pennsylvania School of Veterinary Medicine. They have collected and analyzed thousands of hours of video recordings from hundreds of healthy horses as well as equine patients and have developed a most elaborated Equine Discomfort Ethogram, published in the scientific journal “Animals” in 2021. Their work identifies and classifies a total of 73 pain and discomfort behaviors and depicts them in very instructive drawings. Each category is completed with a videorecording of a patient. All these data are free to access to the public and I can only recommend to at least have a look at the video recordings:

I deem this publication one of the best and most applicable in the realm of equine welfare. The way the paper is structured, and the Ethogram is described and presented by including video material makes it understandable for everyone with an interest in horses. I can only wholeheartedly recommend this to every “horse lover”, lay persons as well as professionals. I believe this publication could really help many of us to recognize pain related behaviors in our four-legged friends.

Another feature horses may exhibit during pain, and which may help us humans to identify pain states is the so-called “pain face”. In recent years, attempts have been made to identify typical features of an equine pain face (Gleerup, Forkman et al. 2015) and to develop rating scales (Dalla Costa, Minero et al. 2014, Dalla Costa, Pascuzzo et al. 2018; the Horse Grimace Scale (HGS)) (https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0092281) for the systematic evaluation of pain in horses measured as typical changes in their facial expression. This publication also depicts a couple of very instructive photographs of equine facial pain expressions.

But how does the equine pain face look like? What cues can we use to figure out, whether our horse is in pain? Figure 1 (adapted from (Gleerup, Forkman et al. 2015) shows a picture of a pain free and relaxed horse. The horse shows attentive ears, the chewing muscles, the muzzle, the nostrils, and the lower lip are relaxed, and the horse gazes with an attentive, open eye.

Figures 2 and 3 (adapted from Gleerup, Forkman et al. 2015) show different variations of an equine pain face: One or both ears are turned backwards, the eye is tense and angled, the gaze is withdrawn or characterized by a tense stare, the nostrils are dilated, the muzzle is tense, and the tonus of the lips, chin, chewing, and mimic musculature is increased. The general impression is that the whole profile flattens.  

I must admit that I found it at first not so easy to identify a pain face in horses however, once you have seen it, it cannot be “unseen”. Moreover, there is also another factor to keep in mind, a stressed horse will also show a facial expression like a horse in pain and of course, this is not surprising and quite similar to humans (remember the discussion of the connection between emotions and pain). However, I do not see the possible confounding with stress as a problem, because pain and stress go hand in hand and the consequences for us handlers are the same, we need to find out, what is wrong and how we can help our four-legged friends.

A pain issue is always a case for a veterinary checkup. Thus, even when uncertain, it is important to have the possible reasons for pain investigated. I do not think that there can be any doubt about this…. However, the challenge for us equestrians and horse lovers lies probably more in how to find out whether our four-legged companion is in pain.

Signs of pain in horses are subtle and their willingness to hide their pain and to please their human makes them particularly vulnerable to be inappropriately treated. Trust your horse! If it is a horse, that you know, think first whether this is a typical or atypical behavior. If this behavior is new, chances are that something is wrong. A horse, that always goes willingly forward and has suddenly lost all motivation, may be in pain and show signs of subtle lameness, that are possibly difficult to pick up. Some horses may even exhibit unwanted or dangerous behaviors, such as bucking and bolting. And what else could they do to protect themselves? Horses have no other means to express themselves and their suffering in particular, because they have no pain sound. Especially in these cases, it is of utter importance to identify, whether the behavior is related to pain. Not only, because anything else would be unethical, but also, because everything else can be dangerous.

Equestrian researchers have made tremendous efforts and progress in identifying pain in horses over the last decade (e.g. check out Dr. Sue Dyson Documentary on the 24 behaviors of the ridden horse in pain: https://www.youtube.com/watch?v=hrZgtrqbMVI ). The identification and description of equine pain behaviors as well as the so-called equine pain face allows for the identification of a possible pain state. It provides a means for us equestrians to identify a potential pain problem so that the appropriate diagnostics and treatment can be arranged for. We as equestrians owe this awareness to our four-legged companions. It is us, the humans, who are responsible for their wellbeing because we control their world, while they have no means to tell us!

References:

All references in this article are “open access” which means that they are freely accessible through the internet and can be downloaded without any charges.

Pain in humans - definition:

Raja, S. N., Carr, D. B., Cohen, M., Finnerup, N. B., Flor, H., Gibson, S., Keefe, F. J., Mogil, J. S., Ringkamp, M., Sluka, K. A., Song, X. J., Stevens, B., Sullivan, M. D., Tutelman, P. R., Ushida, T., & Vader, K. (2020). The Revised IASP definition of pain: concepts, challenges, and compromises. In Pain (Vol. 161, Issue 9, pp. 1976–1982).

https://www.iasp-pain.org/resources/terminology

Pain behavior in horses:

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

https://doi.org/10.3390/ani11020580

Dyson, S. The 24 behaviors of the ridden horse in pain.

https://www.youtube.com/watch?v=hrZgtrqbMVI

Pain face in horses:

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

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0092281

Dalla Costa, E., R. Pascuzzo, M. C. Leach, F. Dai, D. Lebelt, S. Vantini and M. Minero (2018). "Can grimace scales estimate the pain status in horses and mice? A statistical approach to identify a classifier." PLoS One 13(8): e0200339.

Gleerup, K. B., B. Forkman, C. Lindegaard and P. H. Andersen (2015). "An equine pain face." Vet Anaesth Analg 42(1): 103-114.

https://www.vaajournal.org/article/S1467-2987(16)30132-5/fulltext