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Equine veterinary journal2025; 57(6); 1520-1530; doi: 10.1111/evj.14481

Objective assessment of acute pain in foals using a facial expression-based pain scale.

Abstract: Pain assessment based on facial expressions has been described in foals. Objective: To extend previous pilot findings of the Equine Utrecht University Scale for Facial Assessment of Pain in Foals (EQUUS-FAP FOAL). Methods: Prospective blinded case-control study (known groups analysis). Methods: Video recordings (30-60 s) of n = 100 foals (38 patients and 62 controls) were collected. Videos were randomised and scored by two observers, blinded for the condition of the animals. Inter- and intra-observer agreement was tested by Intra Class Correlation (ICC) analysis. Differences between patients and controls were tested using Mann-Whitney U test, differences before and after analgesic treatment were tested with Wilcoxon signed rank test. Multilevel binomial logistic regression was performed for statistical weighting of each pain scale item. Receiver operating characteristic (ROC) analysis was performed to determine sensitivity, specificity and cut-off values. Results: EQUUS-FAP FOAL showed good inter- and intra-observer reliability (ICC coefficient of 0.85 and 0.90 respectively, p < 0.001). Patients had significantly higher pain scores (median score 7, IQR 5.3-7.5) compared with controls (median score 2.5, IQR 1-3, p < 0.001) and the patient pain scores decreased after analgesic treatment (median score 6.5, IQR 5-8 vs. median score 4.5, IQR 3.5-6.5, p < 0.05). Multilevel binomial logistic regression showed the relative importance of the individual scale items. Using the original scale, sensitivity and specificity were 88.2% (95% CI 76%-96%) and 87.9% (81%-98%) respectively, with an area under the ROC curve of 94.9% (92%-98%), based on a cut-off value of ≥4. These values remained similar with the weighted scale based on logistic regression output. Conclusions: Videos of included patients were short and acquired by a person in front of the stable. Conclusions: The current study shows that EQUUS-FAP FOAL can be effectively used to assess acute pain in young foals.
© 2025 The Author(s). Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
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Publication Date: 2025-01-30 PubMed ID: 39888021PubMed Central: PMC12508273DOI: 10.1111/evj.14481Google Scholar: Lookup
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  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study validates the use of the Equine Utrecht University Scale for Facial Assessment of Pain in Foals (EQUUS-FAP FOAL) as a reliable and objective tool to measure acute pain in young foals by analyzing their facial expressions.

Background and Purpose

  • Facial expression-based pain scales have been developed to provide objective pain assessment in animals, including foals.
  • Previous pilot studies suggested the potential of the EQUUS-FAP FOAL scale but required further validation.
  • The objective: to extend the earlier findings by rigorously evaluating the EQUUS-FAP FOAL pain scale’s reliability, validity, and sensitivity in a larger, controlled research setting.

Study Design and Methods

  • The study was a prospective blinded case-control study involving 100 foals: 38 patients experiencing acute pain and 62 healthy controls.
  • Short video recordings (30-60 seconds) of each foal’s face were created to capture facial expressions potentially related to pain.
  • Videos were randomized and evaluated by two independent observers who were blinded to the foals’ health status.
  • Several statistical analyses were performed:
    • Inter- and intra-observer agreement was assessed using Intraclass Correlation Coefficients (ICC).
    • Differences between pain scores from patients and controls were tested using the non-parametric Mann-Whitney U test.
    • Pre- and post-analgesic treatment pain scores in patients were compared using the Wilcoxon signed-rank test.
    • Multilevel binomial logistic regression analyzed the relative importance of each item on the pain scale.
    • Receiver Operating Characteristic (ROC) curve analysis assessed the sensitivity, specificity, and optimal cut-off point for the pain scale scores.

Key Findings

  • The EQUUS-FAP FOAL scale demonstrated excellent reliability:
    • Inter-observer ICC = 0.85, indicating strong agreement between different observers.
    • Intra-observer ICC = 0.90, showing consistent scoring by the same observer over time.
  • Foals experiencing pain had significantly higher median pain scores than healthy controls (7 vs. 2.5), proving the scale’s ability to differentiate pain status.
  • Pain scores in patients decreased significantly after receiving analgesic treatment (median reduction from 6.5 to 4.5), indicating the scale’s sensitivity to changes in pain intensity.
  • Logistic regression highlighted the relative weight or importance of specific facial expression items in the pain scale, confirming a data-driven approach to scale refinement.
  • ROC analysis produced an area under the curve (AUC) of 0.949, reflecting very high accuracy for the scale in detecting pain.
    • At a cut-off score of ≥4, sensitivity was 88.2%, and specificity was 87.9%.
    • The weighted scoring system derived from regression analysis maintained similar diagnostic accuracy.

Conclusions and Implications

  • The EQUUS-FAP FOAL is a valid, reliable, and practical tool to objectively assess acute pain in young foals using facial expressions.
  • The use of short video recordings taken by someone positioned in front of the stable emphasizes the method’s applicability in clinical or on-farm settings.
  • This scale can aid veterinary practitioners and researchers in identifying and monitoring pain more accurately, potentially improving pain management and welfare for foals.
  • By providing an objective measure, the scale reduces subjective interpretation and may enhance consistency across observers and time.

Cite This Article

APA
van Loon JPAM, Trindade PHE, da Silva GV, Keus J, Huberts C, de Grauw JC, Lanci A. (2025). Objective assessment of acute pain in foals using a facial expression-based pain scale. Equine Vet J, 57(6), 1520-1530. https://doi.org/10.1111/evj.14481

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English
Volume: 57
Issue: 6
Pages: 1520-1530

Researcher Affiliations

van Loon, Johannes P A M
  • Department of Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
  • Sporthorse Medical Diagnostic Centre (SMDC), Heesch, The Netherlands.
Trindade, Pedro Henrique Esteves
  • Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA.
  • Laboratory of Applied Artificial Intelligence in Health (LAAIH), Department of Anesthesiology, Botucatu Medical School, São Paulo State University (Unesp), Botucatu, São Paulo, Brazil.
da Silva, Gustavo Venâncio
  • Laboratory of Applied Artificial Intelligence in Health (LAAIH), Department of Anesthesiology, Botucatu Medical School, São Paulo State University (Unesp), Botucatu, São Paulo, Brazil.
Keus, Jiska
  • DAP Suylighem, Zuilichem, The Netherlands.
Huberts, Carlijn
  • DAP De Meierij, Sint-Oedenrode, The Netherlands.
de Grauw, Janny C
  • Department of Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
  • Department of Clinical Sciences and Services, Royal Veterinary College, Hatfield, Hertfordshire, UK.
Lanci, Aliai
  • Department of Veterinary Medical Sciences, University of Bologna, Bologna, Italy.

MeSH Terms

  • Animals
  • Horses
  • Horse Diseases / diagnosis
  • Pain Measurement / veterinary
  • Pain Measurement / methods
  • Case-Control Studies
  • Facial Expression
  • Female
  • Male
  • Acute Pain / veterinary
  • Acute Pain / diagnosis
  • Prospective Studies

Conflict of Interest Statement

The authors declare no conflicts of interest.

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Citations

This article has been cited 1 times.
  1. Bolesławska-Szubartowska J, Kucharczuk M, Skrabska A, Zbysław A, Adamowicz J, Alszko A, Domagalska-Stomska K, Durska M, Dziekcierów A, Janiszewska Z, Korzeniowska R, Kraujutowicz K, Kulesza K, Marciniak P, Pacyna Z, Przeborowska J, Siwek Z, Leonard M, Rapacz-Leonard A. Introducing an Innovative Pain Scale for Assessing Postpartum Pain in Mares: Preliminary Clinical Evaluation.. Animals (Basel) 2025 Nov 30;15(23).
    doi: 10.3390/ani15233454pubmed: 41375512google scholar: lookup
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