Behavioral Laterality, Facial Hair Whorls, and Heart Rate Variability in Horses
The objective of this study was to test for an association between facial hair whorl characteristics and behavioral responses to a fear-inducing stimulus as well as heart rate variability in horses. This was a pilot study in which a small sample size was used. Nineteen well-trained riding horses (7-30 years old) were categorized based on their facial hair whorl height (high, medium, or low), lateral location (right or left of midline), and rotation (clockwise or counterclockwise). Each horse was subjected to a novel object test where an umbrella was suddenly opened as a person approached the horse from the front. The turning response (right or left) was recorded. A Polar RS800CX Heart Rate Monitor was used to continuously measure heart rate and heart rate variability. The standard deviation of the inter-beat interval (SDNN) was used for analysis of heart rate variability. Two horses had double facial hair whorls, and analysis was done both including them in the category of the dominant hair whorl and excluding them. Facial hair whorl rotation showed a correlation with turning response to the fear-inducing stimulus with P = 0.04 including the double hair whorls and P = 0.11 excluding the double hair whorls. Clockwise hair whorls were associated with turning to the right and counterclockwise hair whorls were associated with turning to the left. There were no significant correlations between facial hair whorl lateral location or height and direction turned (P > 0.05). All horses showed a decrease in the SDNN after the presentation of the fear-inducing stimulus (P = 0.0024). Horses with high facial hair whorls showed a tendency for a greater decrease in SDNN compared to horses with medium/low facial hair whorls (P = 0.06). There was no significant correlation between rotation of facial hair whorl or lateral location and heart rate variability (P > 0.05). In conclusion, facial hair whorls are associated with turning response and heart rate variability in horses. Facial hair whorls may be used as a non-invasive method to predict how a horse will respond when frightened and how stressful the event will be. Further studies are needed to develop this method for use by horse owners and trainers.
Keywords: Facial hair whorls; Behavioral laterality; Heart rate variability.