Pain is a physical and psychological experience that occurs when an animal is exposed to elements that could damage their body. While the ability to feel pain is essential for life, pain can also compromise a horse’s welfare or performance, and cause them to behave in undesirable ways.

When pain is detected by specialized nerves called nociceptors, two things happen. First, a signal is sent to the brain. Second, the horse’s brain processes that signal. As every horse is different, some horse brains may ignore or endure the painful sensation, while others will react, and will show a wide range of behavioural responses. This variation in response is what leads to differing levels of pain tolerance among horses.

The limbic system is a group of brain structures responsible for the regulation of emotions and behavioural responses that can aid in survival. Pain is always processed through the limbic system, so when horses experience pain, they also experience unpleasant emotions. Some horses may become anxious or frightened, while others may become irritable or angry. In all instances, the horse will show these emotions through their behaviour.

Pain can be situational, in that it only appears in certain contexts. For example, a horse smacked with a whip will experience pain when struck. Or pain may be chronic, such as with osteoarthritis. While horses display behaviours caused by either type of pain – the whipped horse may kick out, the horse with osteoarthritis may refuse to trailer load – horses experiencing chronic pain are more likely to develop negative changes in their overall mood.

The brain “practices” experiencing pain; the more chronic or severe the pain, the greater the likelihood the horse will experience new pain more severely. This can even result in the horse developing a maladaptive pain condition, where non-painful things like touch are perceived as painful sensations by the horse.

Why pain identification is important

Both short-and long-term pain can be welfare issues that lead to a decreased quality of life, and to negative emotional states such as anxiety, fear, or even depression. Pain also causes chemicals and hormones to be released in the horse’s body that negatively impact physical health and reduce immune responses. Pain depletes a horse’s ability to pay attention to other events happening in the moment; pain can also greatly hamper the ability to learn and perform.

All horses learn through a few basic processes. They learn that their voluntary behaviour leads to consequences that are desirable or undesirable, thus shaping their behaviour in similar future events. Horses also learn through a ‘this predicts that’ process, whereby certain events predict feeling positive or negative emotions. When pain is a regular part of training, such as with osteoarthritis, when a saddle fits poorly, or when techniques like punishment are routinely used, horses often begin to behave in undesirable ways even before the event occurs. For example, a horse experiencing pain in the canter may start to rush in the walk. Or the horse who experiences pain when shod may start to become anxious and difficult to handle when the farrier’s truck arrives on site.

While regular veterinary care is critical to ensure that our horses experience minimal pain, horse owners and trainers are well-suited to spot early indicators of pain by observing changes in behaviour. These changes may be obvious or subtle, depending on factors such as the origin of the pain and how long it has been occurring. Sharp, sudden pain often results in more obvious, dramatic-appearing behavioural responses. Dull, chronic pain can be harder for observers to identify.

Both types of pain can result in behaviours viewed as problematic by owners and trainers. A horse with osteoarthritis may move in an abnormal or restricted manner when ridden, may refuse to trailer load, or may display aggressive behaviours to prevent or delay events which increase their pain. Horses experiencing more situational types of pain – for example a horse experiencing a pinched nerve exacerbated by a particular ridden movement – may buck or bolt, and a horse experiencing dental pain may avoid being bridled.

Thankfully, there is a way horse owners and professionals can detect early signs of possible pain.

Identifying pain in horses

Behavioural observation is a reliable way to identify pain in horses. Standardized pain scales are tools to help identify behaviours consistent with pain in a given species.

Pain scales were developed to identify behavioural differences between animals known to be experiencing pain, and animals not experiencing pain. The scale is then assessed by training observers how to use the scale to score animals, and then having the trained observers score animals whose pain status is unknown to them.

In horses, these scales may focus on a specific part of the body, or they may be composite, considering changes in numerous parts of the horse. Most scales have been tested for specific types of pain in adult horses. For example, the Horse Grimace Scale (HGS) considers slight changes in facial expressions that result from pain, and has been tested with horses experiencing pain because of castration, laminitis, and dental pain. These behaviours can be subtle, such as changes in the horse’s ear position, tension around the eye or jaw, and changes in behaviour related to the chin and mouth.

This subtlety can make it difficult for untrained observers to detect pain in horses. To complicate matters, more obvious behaviours that can be consistent with pain, such as biting, kicking, or bucking, may even be mislabelled by untrained observers; the horse may be called aggressive, dominant, explosive. In such instances, attempts may be made to train the behaviour out of the horse, but the underlying pain will remain. While equine veterinarians are the best professionals for diagnosing and treating pain in horses, even horse owners can learn how to detect early signs of pain which may warrant a call to the vet. By understanding what is normal behaviour for horses, how pain can impact their lives and experiences, and which behavioural indicators may be consistent with pain, we can help our horses experience less pain, sooner.