Validation of the Horse
Grimace Scale
Rochelle McKeown, Caralyn Kemp, Kristina Naden, Nigel Adams
Unitec, Te Pūkenga
Assessing Pain in Animals
• Recognising signs of pain in animals can be challenging but is crucial to welfare
(de Grauw & van Loon, 2016)• Effective pain management strategies rely on correct assessment of pain in real time
• Pain is a subjective experience
(Ijichi et al., 2014)• Pain can be assessed through body language and facial expressions
• Body language is often hidden by the animal
• Facial expressions are often produced
involuntarily
(Mogil et al., 2020)Grimace Scales
• Animals produce grimaces in response to pain
• Validated grimace scales – rats, mice, rabbits, dogs, horses
(see Mogil et al., 2020)• Grimace scales look at facial expressions using the position of ears, nostrils, eyes, cheeks and mouth
• Grimace scales have been validated for their depiction of pain
• Pain assessment responsibility lies with owners, trainers,
therapists etc
(Gleerup et al., 2015)Limitations
• There is limited research on the use of grimace scales by different groups of people
• Testing on the use of GS is typically conducted with veterinarians or vet students
• Training is usually from still images
• Scoring is usually from still images
(e.g. Dalla Costa et al., 2014)• Training in using the grimace scale is thought to
only need to be “short”
Aims/Objectives
• Compare the use of the HGS between different groups of participants before and after training in attempt to test the inter-rater reliability of the scale and investigate the effect of training on HGS scores.
• Hypothesis: training in the use of the
HGS, regardless of previous knowledge
or experience, would result in equalised
scoring between groups of participants
Methodology
• Self-selected groups of participants using an anonymous online survey
• Australia and NZ
• Veterinarians, horse owners/riders, equine physical therapists, animal welfare inspectors, control group (no horse experience)
• Presented with six 5s videos, 3 of horses in pain (within 24hrs of castration) and 3 not in pain (control)
• Provided with training on the HGS (0-2 or unsure) using images from a chart
• Presented with another six 5s videos, again with 3 horses in pain and 3 not in pain
• Participants were blind to the treatment
• Inter-rater correlation testing (ICC; not HGS accuracy)
Dalla Costa et al., 2014
Mean HGS scores (+ SD) by participant group, subject condition, and training status
Treatment Non-treatment Treatment Non-treatment Treatment Non-treatment Treatment Non-treatment Treatment Non-treatment Treatment Non-treatment
Veterinary pro-
fessional Equine Physical
Therapist Horse owner/rider Animal Welfare
Inspector Control Researchers
0 0.2 0.4 0.6 0.8 1
Pre-training Post-training
Participant group and subject condition
HGS score
ICC by group and 95% confidence limits for pre-training facial action unit scorings
ICC by group and 95% confidence limits for post-training facial action unit scorings
Key Findings
• Treatment (post castration) subjects were scored higher HGS than control subjects, irrespective of training
• Both post-castration and control subjects were given higher HGS scores after participants
received training
• Good to excellent reliability between all participant groups both before and after training
• Uncertainty of respondents decreased
following training
Conclusions
• Participants have an indication of pain in horses through facial expressions without extensive
previous knowledge
• Training in the use of Grimace Scales useful for fine tuning pain assessment
• However: framing of the survey: expectation
among participants that the videos presented all represented horses with differing degrees of pain:
bias in responses
• Additional training likely required to use HGS effectively
• Future validation studies needed to control for
these biases and other factors
References
• Dalla Costa, E., Bracci, D., Dai, F., Lebelt, D. & Minero, M. Do different emotional states affect the Horse Grimace Scale score? A Pilot Study.
Journal of Equine Veterinary Science 54, 114–117 (2017).
• Dalla Costa, E. Minero, M., Lebelt, D., Stuckle, D., Canali, E., Leach, M. Development of the Horse Grimace Scale (HGS) as a pain assessment tool in horses undergoing routine castration. PLoS ONE 9, e92281 (2014).
• Dalla Costa, E., Pascuzzo, R., Leach, M. C., Dai, F., Lebelt, D., Vantini, S., Minero, M. Can grimace scales estimate the pain status in horses and mice? A statistical approach to identify a classifier. PLOS ONE 13, e0200339 (2018).
• Dalla Costa, E. Stuckle, D., Dai, F., Minero, M. Using the Horse Grimace Scale (HGS) to assess pain associated with acute laminitis in horses (Equus caballus). Animals 6, 47 (2016).
• de Grauw, J. C. & van Loon, J. P. A. M. Systematic pain assessment in horses. The Veterinary Journal 209, 14–22 (2016).
• Gleerup, K. Assessing pain in horses. In Practice 40, 184(4):124 (2018).
• Gleerup, K. B., Forkman, B., Lindegaard, C. & Andersen, P. H. An equine pain face. Veterinary Anaesthesia and Analgesia 42, 103–114 (2015).
• Ijichi, C., Collins, L. M. & Elwood, R. W. Pain expression is linked to personality in horses. Applied Animal Behaviour Science 152, 38–43 (2014).
• Mogil, J. S., Pang, D. S. J., Silva Dutra, G. G. & Chambers, C. T. The development and use of facial grimace scales for pain measurement in animals. Neuroscience & Biobehavioral Reviews 116, 480–493 (2020).
• van Loon, J. P. A. M. & Van Dierendonck, M. C. Pain assessment in horses after orthopaedic surgery and with orthopaedic trauma. The Veterinary Journal 246, 85–91 (2019).
