Pain Measured

Horses don’t speak, but we can ‘hear’ what they’re telling us if we pay attention. That’s what pinned ears, tail IMG_5943swishing, and lip-licking are all about. Problems arise, though, with the our interpretations: one person can ‘hear’ something different than the next.

Temple Grandin recognized that subjectivity in the cattle industry, where terms like “Properly,” “Adequate,” “Sufficient,” and “Undue Pain and Suffering” once ruled the day.

“What do those terms mean?” she asked rhetorically.

Grandin helped bring measurable protocol to stockyards and slaughter facilities. As a result of her research and lobbying, an increasing number of plants and individual handlers are now scored on the percentage of animals in their care that run, fall, vocalize, and are moved by electric prod. She has arguably made that world a better place for those animals in their final moments. Read article.

Now, researchers have taken steps to quantify what horses ‘say’ about pain. In the recently published “Development of the Horse Grimace Scale (HGS) as a Pain Assessment Tool in Horses Undergoing Routine Castration“ an international team of scientists developed protocol for assessing and measuring horse pain as interpreted through facial expressions. Read their research.

This horse demonstrates low pain, according to HGS.
This horse demonstrates low pain, according to HGS.

They monitored 40 stallions undergoing castration. The studs were divided into two groups, receiving different medications before and after surgery. Another six horses were monitored and managed similarly, but did not undergo surgery. (They had their teeth floated or hooves trimmed.)

The changes in facial expressions were assessed and ranked using the Horse Grimace Scale before and after castration. The Horse Grimace Scale (HGS) asks, for example:

  • Are chewing muscles strained?
  • Are nostrils strained?
  • Is there tightening around the eye?
  • Are the ears back?
The same horse now shows significant pain, according to HGS
The same horse now shows significant pain, according to HGS

The group recorded video footage with two cameras in each stall and selected random still frames to grade the presence or absence of six indicators. Five trained observers evaluated and scored the facial expressions. The researchers pooled and tabulated the results, arriving at HGS scores for all of the horses, before, during, and after the procedures.

Only horses undergoing castration showed high HGS scores.

  • Does this study mean that ranchers, who routinely castrate horses in the field with no sedation or painkillers, are going to change their ways?
  • Might the findings lead to increased scrutiny of those practices which ignore or fail to acknowledge horses’ suffering?
  • Can it help vets, vet techs, trainers, and us Regular Joe horse owners with identifying horses’ discomfort in a wide array of scenarios?

Horses don’t fake it. We can take their expressions at face value and infer that they are experiencing pain. We also assume that heart rate and blood cortisol levels increase with pain. It should be noted that the researchers also collected heart rate and other physiological data in order to study the relationship of those changes with facial expression changes.

Developing a standard to recognize pain in horses is an excellent step towards treating them more humanely. In addition, the Horse Grimace Scale is easy to understand and requires no special equipment. Everyone – from veterinarians to barn workers – can learn to identify HGS markers.

Dr. Emanuela Dalla Costa

“I think that pain assessment in animals is really difficult and probably this is the reason why it is often underestimated. I hope that this study can help people to understand that horses can suffer from painful conditions,” said Dr. Emanuela Dalla Costa, co-author of the study, and a veterinarian and PhD at the University of Milan.

“Horses are a very expressive species. They communicate their emotions and feelings not only with the body posture, but also with their facial expressions. I personally hope that this method can help horse owners in identifying and assessing pain.”

Why the Long Face?

Don’t mistake grazing for zoning out. Horses are still very much alert.

Horses – like zebras, deer, and other large prey animals foraging mostly on grass – have a head that’s perfect for what they’ve been doing for millennia: grazing in mostly open spaces and steering clear of predators.

Despite the perceived calmness and neurological homeostasis in the act of grazing, the horse’s nervous system, fueled by sensory input, is always on some level of alertness. Its senses continually assess and monitor the environment.

The size, placement, and functionality of their eyes, ears, mouth, whiskers, and nostrils are essential to who and what horses are. When you mess with horses’ features through training, care, and management, you unwittingly may cultivate stress or unhealthy situations.

A simple observation of pasture grazing can help us appreciate horses’ beautiful, long-faced design:

The whiskers (better known as vibrissae which have individual nerves to sense forage, novel objects, other horses, etc.) and lips do most of the

Vibrissae, crucial sense organs

investigating on the ground. Not coincidentally, the vibrissae compensate for one of the horse’s blind spots. Trim the vibrissae and you eliminate horses’ crucial sense of feel. Trimming may result in injury and stress, not because trimming hurts. Without this sense, horses are robbed of feel.

The eyes of an average horse are more than 12 inches above its mouth. At first glance, you might think that a grazing horse is looking at the ground. Not so! It’s looking around, scanning for predators or for changes in its environment (like other horses’ movement).

Here’s an equine optics primer, from The Mind of the Horse, by Michel-Antoine Leblanc:

  • Horses have the largest eyes of all land mammals. Their eyes are about eight times bigger than human eyes.
  • They have a large field of vision of about 330 degrees with two small blind spots – right in front of their nose and directly behind them. The horse will check the blind spots by moving its head.
  • Given the visual streak of their eye structure, they see in an ultra-panoramic format. If we had an extra pair of eyes positioned near our ears, we’d have that, too
  • Panoramic perspective, limited color spectrum, and excellent night vision typify equine vision
    Night vision? Horses got that!


Read more about vision here.

Academic research and empirical evidence suggest restraining horses’ heads with rein pressure or by mechanical means (martingales or tie-downs) is precisely the wrong thing to do when encountering tricky footing or obstacles.

The nostrils and horses’ sense of smell may be its most overlooked sense. Both are huge, anatomically and neurologically speaking.

Unlike the other senses, the neural pathway of a horses’ sense of smell does not travel through the thalamus (the sensory relay center that helps integrate sensations into a coherent “this is happening to me” experience).

The olfactory bulbs are situated on the underside of the brain and wired to the brain’s olfactory cortex. Horses may assess predation risk, potential mates, good or bad forage all by smell.

Letting the horse move its head will help it relax and optimize use of its senses

The ears pivot independently. Ten distinct muscles allow them to rotate 180 degrees. Horses can distinguish the direction and distance of sounds and seem to be especially attuned to sounds that could indicate possible threat or a need to move.

Many horses become noticeably more anxious when their hearing is compromised or overwhelmed, like when high winds or loud speaker announcements drown out the more crucial but mundane sounds of their environment.

Horses are motor sensory creatures. Their long-faced features have been shaped over thousands of generations by natural selection (and, to a much lesser extent through domestication) to serve them optimally.

Over time, us humans have gotten away from sensory use:

  • We don’t sniff the air to determine which way it is to the beach. We read a sign or follow a phone app.
  • We don’t evaluate someone’s intention through watching his approach or body movement, we use language: “What’s your intention?”

But for the horse, sensory input, maximized by its long face, rules!