Effect of transportation and social isolation on facial expressions of healthy horses.
Authors: Lundblad Johan, Rashid Maheen, Rhodin Marie, Haubro Andersen Pia
Journal: PloS one
Summary
# Editorial Summary: Facial Expressions in Transportation and Social Isolation Researchers at the Swedish University of Agricultural Sciences examined whether common but potentially stressful management procedures—horse transportation and temporary social isolation—produce measurable changes in facial expressions that might be confused with pain indicators. Using video analysis combined with the Equine Facial Action Coding System (EquiFACS), they recorded 28 horses during trailer transport and a subset of 10 during isolation, whilst monitoring heart rate as a physiological stress marker. Both interventions significantly elevated heart rate (p<0.01) and triggered consistent facial responses including scleral exposure (eye white), nostril flaring, upper eyelid elevation, inner brow raising, tongue protrusion, ear flickering, and increased blink frequency—all statistically significant findings. The concerning implication is that several of these stress-related facial features (notably dilated nostrils, scleral exposure, and inner brow raising) overlap substantially with characteristics currently used in equine pain-assessment tools, potentially compromising diagnostic accuracy and leading to false-positive pain identification in transported or isolated horses. The authors emphasise that distinguishing genuine pain-related facial expressions from stress-related ones requires further investigation to refine the clinical utility of these observational assessment methods in practice.
Read the full abstract on PubMed
Practical Takeaways
- •When assessing horses for pain using facial expression tools, be aware that stress from routine procedures like transport and isolation can produce similar facial changes to pain—context matters in interpretation
- •Dilated nostrils, increased eye white, and ear flickering during stressful management are normal stress responses in healthy horses, not necessarily indicators of pain or illness
- •Development of better pain assessment tools requires distinguishing between stress-induced and pain-induced facial expressions; current facial coding systems may conflate the two
Key Findings
- •Transportation and social isolation increased heart rate (p<0.01) and induced specific facial expressions including eye white increase, nostril dilation, and upper eyelid raising (all p<0.001)
- •Machine-learning classifier achieved 79% accuracy in discriminating stressed horses from calm horses using identified facial action units
- •Several facial features associated with stress in healthy horses (dilated nostrils, increased eye white, inner brow raiser) overlap with pain assessment indicators, suggesting need for further research to differentiate stress from pain expressions