Sympathetic Arousal Detection in Horses Using Electrodermal Activity

Abstract

The continuous monitoring of stress, pain, and discomfort is key to providing a good quality of life for horses. The available tools based on observation are subjective and do not allow continuous monitoring. Given the link between emotions and sympathetic autonomic arousal, heart rate and heart rate variability are widely used for the non-invasive assessment of stress and pain in humans and horses. However, recent advances in pain and stress monitoring are increasingly using electrodermal activity (EDA), as it is a more sensitive and specific measure of sympathetic arousal than heart rate variability. In this study, for the first time, we have collected EDA signals from horses and tested the feasibility of the technique for the assessment of sympathetic arousal. Fifteen horses (six geldings, nine mares, aged 13.11 ± 5.4 years) underwent a long-lasting stimulus (Feeding test) and a short-lasting stimulus (umbrella Startle test) to elicit sympathetic arousal. The protocol was approved by the University of Connecticut. We found that EDA was sensitive to both stimuli. Our results show that EDA can capture sympathetic activation in horses and is a promising tool for non-invasive continuous monitoring of stress, pain, and discomfort in horses.

Keywords: electrodermal activity; horses; sympathetic arousal.

Figure 1

Device placement on the horse’s body.

Figure 2

Samples of normalized skin conductance responses (SCRs) of human and horse.

Figure 3

Ensemble of the normalized power spectrum distribution during feeding for N = 15 horses.

Figure 4

Raw EDA signal and tonic component (top), and phasic component and phasic drivers that are greater than 0.05 µS (bottom) before (baseline) and during the Feeding test for a sample subject.

Figure 5

(a) Boxplot for SCL at pre-feeding and feeding stages (p-value = 0.1049). (b) Boxplot for NS.SCR at pre-feeding and feeding stages (p-value = 0.0281). * Represents statistically significantly differences (p-value < 0.05) between pre-feeding and feeding.

Figure 6

Ensemble of the phasic component for the Startle test from 40 s before the onset of the startle stimulus (umbrella) until 60 s after the stimulus.

Figure 7

The boxplot of mean value of the phasic component of EDA (a) and tonic component of EDA (b) within 20 s segments starting from 40 s before the startle (umbrella) stimulus onset up to 60 s after stimulus onset. Significant differences (if p < 0.05) between segments are presented by a double arrow.