How do horses demonstrate pain?

How do horses demonstrate pain?

An analysis of videos with horse facial features provided new insights into their non-verbal communication of pain.

Evolution equipped almost all animals with sensitivity to pain. Complex pathways behind those unpleasant feelings assure that organisms avoid harmful stimuli and notify individuals about damage bothering the body.

The second case is especially important for anyone caring for animals – as they cannot run away from diseases which can cause pain. At the same time, people often can relieve the animals from suffering by proper treatment, but in the first place we need to notice the pain. This, depending on the species, can be not a trivial task, as some animals avoid any vocalization and have limited facial features. That can be said about horses – which is why scientists tackled the problem with advanced analysis of parts of equine face.

Causing pain to help other horses in pain

In the study, six horses (five mares and one gelding) were subjected to a short period of pain. Scientists placed a tight cuff around a forelimb for no longer than 10 minutes and filmed horse reactions to such “ischemic” pain.

Analysis with EFACS – Equine Facial Action Coding System – surveyed differences in 17 features of horse face. Out of them, researchers confirmed previously known identificators of pain and found a new one.

Indicators of pain sensed by a horse

  • Raise of chin
  • Strained nostrils
  • Rotation of ears
  • Raise of inner brows
  • Half blink

All those features make what scientists called “a horse pain face”. However, usually only some of them are present. Most frequently encountered reactions to pain – raised chin and strained nostrils – were manifested only in half of cases. They were also present in 3 out of 10 situations with no pain. Therefore, the research proposes longer observation of horse’s face, around 10 seconds. In this situation, 90% of horses in pain show at least a few of mentioned reactions – in contrast to pain-free horses, which are closer to 30-60% frequency of at least few features.

As the authors note, quite limited dataset and only six individual horses did not allow to notice large statistical differences.

Progress in pain research

The study is built on previous knowledge about pain communication. In particular, horses were assessed on the basis of images – here, the videos in various length windows (up to 30 seconds) were coded to find new, dynamic features. They succeeded in it, writing in the conclusion:

We defined the “half blink” as a new indicator for pain in horses, and raised some doubts about the pain indicating value of the “inner brow raiser”.

Preprint by M Rashid et al.

The paper is available at bioRxiv: doi:10.1101/2020.03.31.018374

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