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Horse Grimace Scale: An Effective Tool to Quantify Equine Pain

How do I know if my horse is in pain?

This is by far the most common question asked by clients. Many inquisitive owners looking for knowledge on identifying pain indicators in their horse. While we cannot teach every assessment measure learned through post-secondary education, there is a simple scale that anyone can apply quite easily once they know what to look for.

This invaluable tool is the Horse Grimace Scale (HGS).

The research on facial indicators of pain is often overlooked or completely unapplied in mainstream equine practices despite its simplicity. With no equipment required and solely learning through image identification, this scale is a no brainer for the horse owner.

Some of the answers are right in front of us, if we know what we are looking for.

The HGS is a standardized method of assessing for pain through systematic reading of facial expression. Through evaluation of the ears, eyes, jaw, mouth, and nostrils, we may obtain a simple scoring system that is proven to correlate with pain experience in the horse.

This research was conducted in 2014! Almost ten years ago from the time this blog is written yet still unrecognized by many professionals. I am here to change this.

Summarized below are the key points from the journal article to provide ease of understanding. As well, thoughts on therapeutic relevance are provided.

Included in this blog is also a free download of the HGS checklist, so read on till the end to get your copy today.

Emanuela Dalla Costa, Michela Minero, Dirk Lebelt, Diana Stucke, Elisabetta Canali, Matthew C. Leach

Purpose of Study:

To develop and validate a standardized pain scale based on facial expressions in horses.


Forty stallions were assigned to one of two treatments and all animals underwent routine surgical castration under general anaesthesia. Group A (n = 19) received a single injection of Flunixin immediately before anaesthesia. Group B (n = 21) received Flunixin immediately before anaesthesia and then again, as an oral administration, six hours after the surgery. In addition, six horses were used as anaesthesia controls (C). These animals underwent non-invasive, received the same treatment as group A, but did not undergo surgical procedures that could be accompanied with surgical pain. Changes in behaviour, composite pain scale (CPS) scores and horse grimace scale (HGS) scores were assessed before and 8-hours post-procedure.


Only horses undergoing castration (Groups A and B) showed significantly greater HGS and CPS scores at 8-hours post compared to pre operatively. Further, maintenance behaviours such as explorative behaviour and alertness were also reduced. No difference was observed between the two analgesic treatment groups.

The Horse Grimace Scale offers a potential for an effective and reliable method of assessing pain. While auxiliary studies are required to evaluate different painful conditions and analgesic timing, this research paves the way for ethical pain identification of our equines.

Therapeutic Relevance:

Understanding the application of the HGS and being able to recognize common pain indicators can provide the horse owner and therapeutic practitioner with valuable insights. Additionally, understanding how to measure the horse's facial indicators for pain provides a valuable baseline from which to monitor changes. These signs may be combined with the other components of the assessment process enabling a comprehensive evaluation of the horse while identifying specific areas of pain.


HGS_Scoring Sheet_Updated Oct 2023
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