Cannabidiol in the horse: Effects on movement and reactivity
A growing body of research supports the investigation of cannabidiol (CBD) for treatment of conditions involving inflammation, pain, and anxiety. Exploration of CBD supplementation has occurred in rats, canines, felines, and humans. However, few trials exist on CBD efficacy in the horse. This project investigated effects of extended CBD treatment on reactivity and movement in horses. Seventeen Quarter Horse geldings were randomly assigned to a control (CON; n = 8) or treatment (TXT; n = 9) group. Treatment horses received a 100 mg oral dose of full-spectrum CBD pellets once daily for 6 wk. Reactivity and movement evaluation occurred pre- and 6 wk post-treatment. Reactivity was evaluated through a novel object test (NOT). To elicit a startle response, an umbrella was opened as the horse and handler traveled around a barn corner. A previously published rubric was used to rate reaction scores from 1 (no reaction) to 5 (flee attempted) based on the reaction exhibited. Heart rate monitors were attached during the NOT. Videos for movement evaluation were taken as horses were hand walked and jogged past 6 cones. Dartfish 360, a video analysis program, was used to measure aspects of stride completion. This included stride length and duration of stance and swing phase. Measurements were completed on a 3-stride sequence for each limb within the 9.14 m between cones 3 and 4. Chi-squared analysis was completed via the PROC FREQ procedure of SAS to determine the relationship between CBD treatment and reactivity. Effects of treatment on initial heart rate (IHR), stimulus heart rate (SHR), and final heart rate (FHR) were analyzed through the PROC MIXED procedure of SAS. Statistical analyses were completed for stride length (SL) and time spent in stance (ST) or swing phase (SW) for walk and trot using PROC MIXED procedure of SAS. An average of the 4 limbs was calculated for each horse for each parameter. Treatment horses received a lower frequency of moderate (3) to high (4, 5) reactivity scores compared with CON (TXT = 24; CON = 37; P = 0.0018). Statistical significance was not observed for IHR, SHR, or FHR. Further investigation is needed to accurately characterize the role of CBD in alterations of equine behavior. In walk, TXT horses spent longer in ST (TXT = 0.57 s, CON = 0.51 s; P < 0.01) and SW (TXT = 0.38 s, CON = 0.36 s; P < 0.01). Both groups demonstrated a reduction in trot SL (Pre = 1.68 m, Post = 1.55 m; P = 0.03) and stride completion (STPre = 0.30 s, STPost = 0.26 s; P < 0.01; SWPre = 0.37 s, SWPost = 0.33 s, P < 0.01). Results on stride kinematics were relatively inconclusive. Future studies could benefit from the observation of equine subjects with a targeted physical ailment or increased CBD dosage.