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  • Cortisol is a natural glucocorticoid hormone


    Cortisol is a natural glucocorticoid hormone produced by the adrenal cortex. Its secretion is stimulated by the sympathetic nervous system, and its main function is to mobilize energy to protect the homeostasis of vital biochemical processes during physical and psychological stress [14]. Chronic levels of elevated cortisol are also known to be correlated in a suppression of cellular and humoral immunities [16]. The effects of chronic stress can prove to be detrimental for therapeutic horses. Improving the way to scientifically assess the HPA response in horses involved in EAAT is essential to determine how the horses are coping with their interaction with humans involved in such activities [17]. Oxytocin is a neuropeptide consisting of nine galanin receptor produced by the paraventricular and supraoptic nuclei of the hypothalamus and has important roles in social behaviors, including reproduction and parenting. In addition, the literature shows that oxytocin is also responsible for both the causes and effects of positive social interactions resulting in a general feeling of mental and psychological well-being [18], [19]. Oxytocin, released during forms of positive social interaction, may be responsible for buffering the sympathetic responses of the ANS, such as blood pressure and HR [20]. Oxytocin has antistress effects by reducing glucocorticoid stress hormones in humans and animals and is associated with increases in parasympathetic function [9]. Research has shown that interacting with animals stimulates the production of circulating oxytocin, which is known to have calming effects on the body and to aid in relaxation [21]. Work investigating positive human-canine interactions demonstrated that a significant decrease in blood pressure was found in both humans and dogs and that plasma oxytocin increases in both species, whereas plasma cortisol decreased in humans only [22]. An exploratory study looking at the interactions between people and dogs showed that physical interactions such as petting and stroking resulted in several hormonal and physiological responses in the dogs. It was noted that oxytocin concentrations significantly increased and HR significantly decreased in dogs that had interacted with people in comparison with dogs without human interactions [23]. Similar HAIs occur during EAAT. Heart Rate Variability is a noninvasive measure of autonomic nervous activity and is defined by the natural variation in time between consecutive heartbeats. The most common reason for these variations is a deviation from the normal autonomic function [24], thus making HRV one of the most promising markers for increased sympathetic or reduced vagal activity [25]. The power spectra of HRV in the high frequency (HF) power is thought to reflect parasympathetic nervous function, whereas the low frequency (LF) power reflects both the sympathetic and parasympathetic nervous systems. The LF/HF ratio is considered to be an index of cardiac sympatho-vagal balance [26]. Research suggests that HRV analysis can be used to characterize psychological disorders such as depression, panic disorder, and anxiety. Heart rate variability analysis has shown that sympathetic activity increases and parasympathetic activity decreases during mental or emotional stress and that recall of anger increased sympathetic outflow to the heart, whereas feelings of appreciation decrease sympathetic and increased parasympathetic outflow [27]. Walking the dog resulted in increased HRV compared with walking alone, suggesting a relaxed state and an increase of parasympathetic activity [23].
    Materials and Methods
    Discussion Cortisol and HRV were chosen as physiological markers of stress in this study. Glucocorticoids have been widely used in animal welfare research as an animal-based assessment of welfare. Activity of the ANS can be evaluated indirectly by HRV [11]. Regarding plasma cortisol, all horses displayed normal physiological concentrations of the hormone throughout the experiment, and one hour session of EAAT resulted in no change from baseline concentrations or from standing controls, which is in contrast to earlier work, which reported abnormally high concentrations of cortisol in horses used in a therapeutic riding program [8]. Another study hypothesized that horses used in therapeutic riding programs would exhibit greater increases in cortisol concentrations before, during, and after a therapeutic riding lesson, due to the challenges these riders face personally, when compared with a traditional hunt seat lesson with experienced riders, only to find that there was no difference in cortisol between the groups [10]. Although the stress response may be initiated after an exhausting physical challenge, most equine-related activities are not that physically demanding and therefore the stressor is more likely psychological [34]. Another study measured the stress response to equestrian sports and found that cortisol concentrations increased during the riding phase of the activity but returned to baseline within 30 minutes of completion. There was also an increase in sympathoadrenal activity, indicated by an increase in HR, which occurred in the stable area during grooming and saddling of the horses [35]. One study demonstrated lower cortisol concentrations in horses used in therapeutic riding at 5 and 30 minutes postsession indicating that the therapeutic riding session had small effects on the HPA response [36].