Eye Blink Rates and Eyelid Twitches as a Non-Invasive Measure of Stress in the Domestic Horse.
Authors: Merkies Katrina, Ready Chloe, Farkas Leanne, Hodder Abigail
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary: Eye Blink Rates as a Stress Indicator in Horses Researchers evaluated whether changes in spontaneous blinking and eyelid movements could serve as practical, non-invasive markers of equine stress, comparing these behavioural measures against heart rate responses during four different scenarios: normal paddock conditions, feed restriction, social separation, and a startle test across 33 horses. Video analysis revealed that both full blinks and half blinks decreased significantly during all three stressor conditions—with full blinks dropping from 16 per three minutes in control conditions to 13 per three minutes during separation, and half blinks declining from 34 to 25 per three minutes across the same comparison—whilst eyelid twitches paradoxically increased (particularly during feed restriction) alongside elevated heart rates. The inverse relationship between blink suppression and stress appears consistent across different types of stressors, suggesting that reduced eyelid movement reflects genuine physiological stress responses rather than simple fatigue or environmental variation. For practitioners working with horses, monitoring eye blink patterns offers a rapid, equipment-free assessment tool that could complement existing behaviour and heart-rate observations during handling, transport, training or veterinary procedures, potentially enabling earlier detection of stress-related welfare concerns.
Read the full abstract on PubMed
Practical Takeaways
- •Monitor eye blink patterns and eyelid twitches as quick, non-invasive indicators of stress in horses during handling, transport, or management changes — increased twitching and decreased blink rates signal acute stress
- •Changes in blink behaviour may help identify when horses are experiencing stressful situations (feed disruption, separation, or fear-inducing events) before more obvious stress signs appear
- •Use eyelid movements alongside heart rate monitoring for rapid stress assessment in field conditions where other physiological measurements are impractical
Key Findings
- •Full blink rates increased significantly during startle test (26±20 blinks/3min) compared to control, feed restriction, and separation conditions (13-16 blinks/3min, p<0.006)
- •Half blink rates decreased during feed restriction, separation, and startle test (25-27 half blinks/3min) compared to control (34±15 half blinks/3min, p<0.0001)
- •Eyelid twitches increased significantly during feed restriction compared to other conditions (p<0.0001) and correlated with elevated heart rate (p<0.0001)
- •Spontaneous eye blink rate and eyelid movements provide non-invasive behavioural indicators of acute stress in horses