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Detecting equine pain

by Frauke Musial & Celina Skogan

Why we wrote this article - Celina Skogan

 

Did you follow the latest studies in equine orthopedics? One was broadly shared on Facebook. It was a study by the world renowned equine vet Sue Dyson. She published about subtle lameness in horses, and the signs horses are showing during training. In the past, the grand dame of orthopedics always stood out as an advocate for the horse. Her latest efforts in rising awareness to the equine condition in therapists, trainers as well as horse owners is therefore no surprise.  What was surprising though was the public response. A more than average amount of people had to admit that they were unable to detect the lameness shown on screen. 
That might explain why we see, even in our time and age when riding is a choice , not a necessity, so many horses with unclean gates in any average riding arena. Often, pain is not recognized in early stages, where it might be “just” an issue of bad training, natural unstraigthness or imbalance, but nonetheless, the issue is already established in the equine body. Even more often, problems are first recognized when severe bone or tendon damage occurs (such as arthrosis, kissing spines, etc.). It cannot be emphasized often enough that pathologies in the hard tissue / bone structures are appearing late, and after the soft tissue has been damaged for a very long time, undetected. Fascial or muscular issues, and everything that is categorized in the field of subtle lameness, appears to be even more difficult to spot. I guess that is a good for reason for ambitious scientists to pick up on that topic, trying to categorize pain issues and signs.  

Science is taking a first step towards what a well-schooled trainer or rider should be able to detect in the blink of an eye.

 


The equine «pain face»

 

Horses, similar to other prey animals, are not able to communicate pain vocally. They do not have a pain sound. This distinguishes horses from other animals who may live in close proximity or in a more or less symbiotic relationship with humans such as dogs and cats. In addition, the fact that horses express pain more subtle and in silence imposes a challenge for horse husbandry and welfare. In particular, since painful procedures such as castration or branding are routine practice in horse management. Fortunately, there has been increasing awareness of pain in animals and considerable efforts have been made in order to physiologically understand and to alleviate pain in animals, including the horse.

 

Nonetheless, even though there has doubtlessly been considerable progress in how to treat pain states in horses, how to diagnose and determine pain in an animal, which expresses pain very subtle and without vocalization remains a challenge.

 

In addition, several behavioral scientists suggest, that horses may even suppress pain expressions when a human is present. Such a behavior would be typical for a prey animal in a vulnerable situation, especially with a predator (the human) present.

 

 

Attempts to measure pain in horses are often based on behavioral measures and/or biomarkers such as heart rate. Nonetheless, behavioral measures are difficult to interpret as a horse can be agitated or in agony during pain. Biomarkers, such as e.g. heart rate suffer the disadvantage that they may not be able to distinguish a stress reaction from a pain state.

 

Over the last decade, the focus has shifted towards facial expression and facial expression scales have been developed for laboratory animals such as mice and rats. 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) for the systematic evaluation of pain in horses. The results of these studies conclude that there is a typical pain face in horses, even though the changes are subtle.
The good news is that primates, which includes us humans, are as social animals very good in interpreting emotions through facial expressions, even when a person is trying to hide their emotions.

 

 

But how does the equine pain face looks like? What cues can we use to figure out, whether our horse is in pain and not just stressed? 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.

 

 

Based on these characteristic features Dalla Costa and coworkers ((Dalla Costa, Minero et al. 2014) have developed a pain rating scale for horses, the Horse Grimace Scale (HGS) which has been proven to be a useful instrument for the assessment of equine pain states (Dalla Costa, Pascuzzo et al. 2018). For readers, who are interested in deepening their knowledge and would like to see more pictures and descriptions of horse pain faces, all references below in this article are “open access” which means that they are freely accessible through the internet and can be downloaded without any charges.

 

 

To be able to identify a pain state in a horse is relevant for everybody who rides or handles horses. Moreover, I find it also a fundamental matter of an ethical attitude that comes with the responsibility of a rider or horse owner. I have myself experienced, that an unwillingness of my horse to go forward, which, as I know well now, was related to him experiencing pain, was interpreted as unwilling behavior by a riding instructor with a clear instruction towards me, to not “let him go away with it” and ride forward with whatever means it took.

 

 

The episode elucidates two things:

 

i)                    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. Some may exhibit unwanted or dangerous behaviors, such as bucking, because they have no other means to express themselves. In these cases, it is really important 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.

 

ii)                   Trust your horse! If it is a horse, that you know or even your own, 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.

 

Changes in a horse’s behavior can have many reasons, e.g. stress due to events which happened in the herd, possible changes in the environment, that are new and may feel awkward, other health problems, which make the horse feel uncomfortable. The identification and description of the equine pain face allows for the identification of a possible pain state related to unwanted behavioral changes. It provides a means for us equestrians to identify a potential pain problem more easily so that the appropriate diagnostics and treatment can be arranged for. We as equestrians owe this awareness of potential pain states to our four legged companions, we are responsible for their well-being, because they have no means to tell us!

 


Practical tips for every day

Especially when the exercises advance, the horse should show an attantive, but open face.
Especially when the exercises advance, the horse should show an attantive, but open face.

 

As a trainer or horse owner, what is it that you can do in your everyday life to detect issues early, before pain is established or for detecting pain early?

Listen to your horse – literally.

If you do have the chance, ask someone to lead your horse over hard surface. Close your eyes and listen to the beat. It helps to mentally count the beat – meaning, 1-2-3-4 in walk and 1-2 in trot. Is the beat even? Is one step softer or harder? Is one beat longer or shorter?
When lunging, try as well to count the beat in canter. A clean, normal canter is a 3-beat. Count 1-2-3.
Use each possibility to look at horses in the arena, for training your eye and schooling your ear.

 

 

 

Listen to your own body – some signs of stiffness
When you are sitting at your horse – is the beat clean? Do you feel one hoof harder than the others? Is it easy to sit in trot, or do you prefer rising trot? If your horse feels uncomfortable in trot and canter, chances for backpain in your horse are very high.

Look at your horse from behind – some signs of hip or lumbar issues
Do both sides of the pelvis / hip move evenly? Do both hindlegs step straight, without any twisting or turning in fetlock or hoof? Do both hindlegs have the  same length of a step? Is the tail swinging evenly from right to left and back?

 

Look at your horse from the side – some signs of imbalance.
How are the legs moving? How is the balance? Is the horse leaning towards  one side? Is it using one diagonal more than the other? Are the front legs swinging forward straight? Is your blacksmith complaining about one hoof being used more / being smaller or bigger?

 

Look at your horse from the front – signs of lameness in the limbs.
Is the head moving left - right and up-down evenly? Or is one leg / one diagonal emphasized more?  Are all hooves lifted from the ground? Or is one / more scratching the surface?

 

Touch our horse!
Detect any changes in warmth / coldness. Have you checked the DIY-Massage (1) ? Check it out! If your horse is reacting very sensitive on a certain spot when you feel the upper line, chances for an issue there are high.

 

Changes in behavior /behavior issues
Is your horse suddenly changing? Is it not its normal happy self? Is it chewing on just one side?
Or is it generally not happy to be touched or brushed. Is it flattening the ears when you come with a saddle? Turing away the head when you show a halter or bridle? Is it difficult for the blacksmith to pick up all four hooves? Can you easily brush all hooves? Is your horse grumpy, biting? Is it showing signs of pain when seeing the saddle? Can it stand alone and with loose reins on the mounting block? Is it grumpy when fastening the saddle girth?

 

 

If you answer just one of these questions with no, it is your horse communicating you that it doesn’t feel well.  Remember that a vet is not a professional rider, and a trainer does not have to be well schooled in biomechanics. You, as a horse friend or a horse owner, as a rider and caretaker, do have the responsibility to detect possible problems as early as possible and to respond to your horses needs. We all can have a bad day, but we cannot have a bad week. Get help and clarification as soon as possible.

Each rider has also the responsibility to say “NO” to riding if e.g. a school horse is not sound. If you need more strength for pushing, if the jump is too high, if your horse needs “extra motivation” from a more distinct bit, the whip or more and more leg use or if your trainer tells you to “ride over it”. Either the exercise is simply not on your level, and then only better preparation and time will help, or your horse is in serious trouble. For the sake of your own safety and the well-being of the horse, be truly brave and say no. 


 

References:

 

For readers, who are interested to deepen their knowledge about the facial expression of pain in horses: All references in this article are “open access” which means that they freely accessible through the internet and can be downloaded without any charges.

 

 

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.

 

 

 

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.

 

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