A new study has shown that which eye a horse uses to look at a new object may affect his heart rate, giving clues to his stress level.
The two hemispheres of the equine brain have important functional differences, particularly regarding the sensory systems. The left hemisphere seems to be involved in the analytical categorization of stimuli; the right hemisphere processes negative stimuli and responds to threats, causing a stress response.
Dr. Martina Felici of the University of Pisa in Italy noted that the eye a horse uses to look at novel stimuli may help detect a horse's stress level in a non-invasive way. She said that these findings may have physiological and behavioral consequences, as well as possible practical implications for horses.
To test their theory that eye use affects cardiac response, the researchers used 20 horses, 11 mares, and nine geldings from two stables. They tested the horses by rapidly inflating an orange balloon in their presence.
The team predicted that horses using their left eye (the right hemisphere of their brain) to look at the balloon would have a greater degree of variability seen on electrocardiograms (therefore, would be more stressed), compared to horses that used their right eye to look at the novel stimuli (and used the left side of their brain).
Each horse was videoed to determine which eye it used to look at the balloon and had a five-minute EKG recorded. The horse was not tied, so was able to view the balloon out of whichever eye it preferred.
Five minutes of electrocardiograms were recorded for each horse, and video analysis was used to determine which eye each of the horses used to view the balloon. The balloon was presented randomly depending on where each horse was positioned in the stall.
They found that horses that spend longer looking at the balloon with their left eye had ECGs that showed greater variability than the horses that looked at the balloon out of their right eye, supporting the hypothesis that horses that looked at novel objects out of the left eye had more emotional reactions.
The scientists concluded that which eye a horse uses to look at a novel object can be related to a horse's heart rate response, which can reflect that the animal is stressed.
Read more at HorseTalk.
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