Effects of chiropractic manipulations on behavioral and physiological parameters in healthy horses: A preliminary investigation

Abstract

Human chiropractic is a well-established, evidence-based complementary medicine. Contrariwise, there is a lack of research on its impact on horses. This study aimed to evaluate the effects of chiropractic treatment on healthy horses by measuring behavior, maximum temperature of the eyes (MaxTE), salivary cortisol (SC), and heart rate variability (HRV). Eight mares were selected and exposed to a 15-day habituation period. Then, they were randomly assigned to a grooming (GROOM) or chiropractic (CHIRO) session, performed by the same qualified chiropractor. The experiment was designed as a cross-over study and repeated after a 10-day washout (i.e., Week 1 and Week 2). During-CHIRO, the chiropractor treated and recorded joint hypomobility. During-GROOM, the mares were subjected to a standardized grooming session. MaxTE and SC were obtained before (T0), immediately after (T1), and one day after (T24) both sessions. In addition, before (Pre), during (During), and after (Post) both sessions, the mares were video recorded, and heart rate for HRV analysis was taken. Videos were analyzed using a specific ethogram and a Behavioral Discomfort Score (BDS) was obtained. Results showed that the mares manifested temporary signs of discomfort During-CHIRO, highlighted by an increase of ‘avoidance movements’ (p < 0.001) and ‘alert’ (p = 0.038). This was confirmed by an increase in BDS During-CHIRO (p = 0.044). No sympathetic shift was shown by MaxTE, SC, and HRV. A significant increase in the standard deviation of RR intervals (SDNN) suggested a parasympathetic shift in Post-CHIRO (p = 0.040). Joint hypomobility tended to decrease between the first and second CHIRO (p = 0.09). Our results showed that equine chiropractic could be performed by a qualified veterinary chiropractor, leading to transient discomfort behavior, not accompanied by acute stress response. On the contrary, there seems to be a subsequent relaxation, demonstrated by an autonomic nervous system shift toward the parasympathetic branch. Consequently, chiropractic manipulation could be considered as an integrative treatment to improve the horses’ welfare.