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Facial Expressions of Horses Using Weighted Multivariate Statistics for Assessment of Subtle Local Pain Induced by
Júlia R G Carvalho1, Pedro H E Trindade2, Gabriel Conde1
1Department of Animal Morphology and Physiology, School of Agricultural and Veterinarian Sciences, São Paulo State University, FCAV/UNESP, Jaboticabal 14884-900, SP, Brazil.
Animals : an Open Access Journal From MDPI
|September 23, 2022
Summary
Facial expression analysis methods failed to detect low-grade pain in horses after polymer implantation. Objective measures like cutaneous temperature and nociceptive threshold showed changes, but facial expression scores did not reliably indicate pain.
Area of Science:
- Veterinary Science
- Animal Welfare
- Pain Assessment
Background:
- Facial expression analysis is a common method for assessing pain in horses.
- Polylactide-based polymer implantation is a veterinary procedure requiring pain evaluation.
- Objective pain indicators may not always correlate with observable facial expressions.
Purpose of the Study:
- To evaluate the efficacy of five statistical methods for facial expression analysis in detecting pain in horses.
- To compare facial expression analysis with objective measures like mechanical nociceptive threshold and cutaneous temperature following polymer implantation.
- To determine if facial expression analysis can identify low-grade inflammatory pain in horses.
Main Methods:
- Horses underwent either polymer implantation or a sham surgical incision.
- Facial expressions were filmed before and at 24 and 48 hours post-procedure.
- Five methods were used to analyze seven facial expressions: individual scoring, SUM, Principal Component Analysis (PCoA), SUM.W, and General Facial Score (GFS).
- Mechanical nociceptive threshold (MNT) and cutaneous temperature (CT) were measured concurrently.
Main Results:
- No significant intra- or intergroup differences were found using individual facial expression scores or the General Facial Score (GFS).
- The control group exhibited higher SUM, PCoA, and SUM.W scores at 48 hours post-procedure compared to the implanted group.
- Despite non-significant facial expression results, implanted horses showed greater alterations in CT and MNT.
Conclusions:
- The five tested facial expression analysis strategies were insufficient for detecting low-grade inflammatory pain in horses.
- Objective measures (CT, MNT) provided more sensitive indicators of pain than facial expression analysis in this study.
- Further research is needed to refine facial expression analysis techniques or rely on complementary objective pain assessment methods in equine veterinary practice.
