Effects of Incorporating Horses into Occupational Therapy on Adrenocortical and Sympathetic Nervous System Reactivity and Regulation in Autistic Children: A Randomized Controlled Trial

Purpose: The study prospectively investigated adrenocortical and autonomic nervous system reactivity and regulation as autistic children participated in a randomized controlled trial of occupational therapy in an equine environment (OT-Equine). Methods: Autistic children (n = 72, ages 6–11 yrs) were randomly assigned for 10 weeks to OT-Equine or clinic-based occupational therapy (OT-Clinic). Saliva samples (later assayed for cortisol and alpha-amylase, [sAA]) were collected before (pre-session), during (within-session), immediately after (post-session), and 20-minutes after (post-session + 20) each 1-hour weekly session. Data were analyzed with a generalized linear mixed-effects model. Results: Across the 10 sessions, pre-session sAA significantly increased (exp(b) = 1.02 per week, p < 0.05). Within sessions, sAA increased (exp(b) = 1.22; p < 0.01) during therapy and recovered post-session + 20. Group differences in sAA changes were non-significant. By contrast, pre-session cortisol concentrations were stable across the 10-weeks (exp(b) = 1.01; p > 0.05). Within session, however, cortisol concentrations decreased from pre- to post- and post-session + 20, with greater reductions among OT-Equine participants (exp(b) = 0.77; p < 0.01). Changes in cortisol were associated with improved treatment outcomes. Conclusion: The pattern of reactivity and recovery in sAA suggests that children experienced autonomic/sympathetic arousal in response to therapy sessions, perhaps associated with excitement and positive affect. Moreover, stable pre-session cortisol concentrations across sessions for both groups, and declining cortisol concentrations within sessions for the OT-Equine group, suggests OT-Equine participants also held subjective experiences characterized by familiarity and low levels of distress. Taken together, findings suggest the integration of horses into occupational therapy for autistic children creates an exciting positive therapeutic environment, associated with improved treatment outcomes. The study was registered as a clinical trial at clinicaltrials.gov (NCT05846932, registered April 26, 2023).