Eye Blink Rates and Eyelid Twitches as a Non-Invasive Measure of Stress in the Domestic Horse
2019
Katrina Merkies | Chloe Ready | Leanne Farkas | Abigail Hodder
Physiological changes provide indices of stress responses, however, behavioural measures may be easier to determine. Spontaneous eye blink rate has potential as a non-invasive indicator of stress. Eyelid movements, along with heart rate (HR) and behaviour, from 33 horses were evaluated over four treatments: (1) control&mdash:horse in its normal paddock environment: (2) feed restriction&mdash:feed was withheld at regular feeding time: (3) separation&mdash:horse was removed from visual contact with their paddock mates: and (4) startle test&mdash:a ball was suddenly thrown on the ground in front of the horse. HR data was collected every five s throughout each three min test. Eyelid movements and behaviours were retrospectively determined from video recordings. A generalized linear mixed model (GLIMMIX) procedure with Sidak&rsquo:s multiple comparisons of least squares means demonstrated that both full blinks (16 ±: 12b vs. 15 ±: 15b vs. 13 ±: 11b vs. 26 ±: 20a full blinks/3 min ±: SEM: a,b differ p <: 0.006) and half blinks (34 ±: 15ab vs. 27 ±: 14bc vs. 25 ±: 13c vs. 42 ±: 22a half blinks/3 min ±: SEM: a,b,c differ p <: 0.0001) decreased during feed restriction, separation and the startle test compared to the control, respectively. Eyelid twitches occurred more frequently in feed restriction (p <: 0.0001) along with an increased HR (p <: 0.0001). This study demonstrates that spontaneous blink rate decreases while eyelid twitches increase when the horse experiences a stressful situation.
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