Psychophysiological effects of equine-facilitated psychotherapy on Veterans with PTSD and their horse partners.

Introduction: Animal-assisted therapies (AATs) are used to promote the mental and physical health of humans. Research using subjective assessments of psychotherapy incorporating horses (known as equine-facilitated psychotherapy, or EFP) for Veterans with posttraumatic stress disorder (PTSD) demonstrated positive effects on PTSD and comorbidities. Although EFP appears to positively influence human mental health, published physiological data are lacking, and little is known about the horses' responses. Methods: To determine the efficacy of EFP with Veterans with PTSD and the effect on horses through measurements of human-horse dyads, a prospective cohort design was used consisting of four eight-week EFP interventions for Veterans with PTSD. Changes in stress hormones and heart rate variability (HRV) in humans and horses, along with PTSD symptoms in humans and behavioural responses in horses, were recorded. Results: In humans, average daily measures of cortisol decreased and average daily oxytocin concentrations increased after each session. Additionally, daily self-reports of mood, anxiety, and well-being improved after each session. The Sympathetic Nervous System Index increased and Parasympathetic Nervous System Index decreased after daily sessions. Horses showed no significant difference in HRV, oxytocin, or observed stress behaviors. However, a significant decrease was observed in cortisol from pre- to post-session. Discussion: These findings indicate that EFP had psychological and physiological benefits for individuals with PTSD with no concomitant negative physiological effect on the welfare of horses. Biological metrics combined with human psychological and equine behavioural measures enhance understanding of the effect of EFP on the dyad participants.