I feel your pain: Individual differences in welfare indicators after castration in horses.
Authors: Briefer-Freymond Sabrina, Dalla Costa Emanuela, Jolivald Aurelie, Bruckmaier Rupert M, Atallah Elie, Giorgia Riva Maria, Ijichi Carrie
Journal: Veterinary journal (London, England : 1997)
Summary
Castration remains a common equine procedure, yet individual horses show markedly different pain responses that aren't fully explained by standard physiological measures alone. Researchers monitored 19 horses undergoing surgical castration, measuring infrared eye temperature, salivary cortisol, the Horse Grimace Scale (HGS) and pain-related behaviours before, during and after the procedure. All four indicators changed significantly post-castration (p < 0.005–0.03), but individual variation was substantial and inconsistent within horses—suggesting that personality traits substantially modulate pain expression. Notably, horses scoring higher for neuroticism showed lower cortisol responses (estimate = −0.275), whilst more extroverted individuals displayed elevated cortisol (estimate = 0.406), and the veterinarian's technique appeared to influence outcomes, emphasising the skill-dependent nature of surgical pain management. The HGS emerged as particularly valuable for clinical practice, as this facial pain indicator correlated with cortisol levels (r = 0.568) and wasn't confounded by personality differences, offering farriers and veterinarians a potentially reliable, standardised tool for recognising pain at the individual level—though the authors note that larger, more methodologically standardised studies are needed to establish HGS sensitivity across different surgical protocols and baseline welfare states.
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Practical Takeaways
- •The Horse Grimace Scale may be a reliable tool for objectively assessing pain in individual horses regardless of their personality type, potentially improving pain recognition and management decisions
- •Consider that personality traits (neuroticism and extroversion) influence how horses physiologically respond to painful procedures; more extroverted horses may show larger cortisol elevations requiring attention to their welfare
- •Veterinarian technique and skill significantly affect how horses respond to castration, emphasizing the importance of selecting experienced practitioners and maintaining high standards of clinical execution
Key Findings
- •Eye temperature, salivary cortisol, Horse Grimace Scale, and maintenance behaviour all significantly changed from baseline following castration (p<0.03)
- •Personality traits explained differences in cortisol responses, with Neuroticism negatively associated (estimate=-0.275, p=0.035) and Extroversion positively associated (estimate=0.406, p=0.001) with pain response magnitude
- •Horse Grimace Scale was not confounded by personality and correlated with cortisol levels (r=0.568, p=0.027), suggesting it reflects underlying affective pain states independent of individual differences
- •Clinician skill appeared to influence individual pain responses, though physiological and behavioural responses were not consistent within individuals across measurement intervals