The effect of citrus botanical oil on equine behavior

The equine industry uses calming supplements to help horses cope with the stressors of interacting with humans and to improve safety through behavioral modification. This study tested the hypothesis that ZenRG® (Equinutrix, Cheritan, VA), a novel blend of citrus botanical oils, magnesium, and yeast would reduce the number of negative behaviors exhibited by young (1.5-6 years of age) horses (n=14) participating in an academic training program. During the 2 mo feeding trial, horses were assigned to either a control (CON, n=7) or treatment (TRT, n=7) group and received groundwork training 4 d per wk. The TRT group received the supplement, top dressed onto their feed, once daily (per manufacturer’s recommendations) the CON group received the same daily ration, no supplement. Horses were housed in individual stalls for the study period with daily turnout to a dry lot or hand walking in the middle of the day (15 – 30 min). Horses underwent an anxiety-test prior to the start of the study. This consisted of taking two horses to an outdoor pen containing a round pen at one end. The test horse was released next to a feed bucket at the far end of the pen, while the companion remained in the round pen with an additional feed bucket. Time spent in proximity to the companion vs. feed was measured for the test horse, and positive and negative behaviors scored. Scores were used to block horses to treatments. This test was repeated at the end of the study. On d 0 and d 58 of supplementation blood samples were obtained between 0600-0630, 100-1030, and 1400-1430 for analysis of plasma cortisol concentrations. On d 19 horses underwent a 10 min isolation-tying test were blood samples were obtained pre, immediately after, and 1 h post. Horses were recorded via camera for analysis of behaviors (content behaviors, licking and chewing, standing quietly vs stress behaviors, pawing, setting back, walking, biting). On d 52 or 55, horses wore heart rate monitors during a 15 min trailering test (TT), and were recorded by camera to count time spent performing stress behaviors (pawing, defecating, vocalizing). On d 56, horses underwent a startle test (ST), during which time to travel 10’ and total distance traveled after being acoustically startled were recorded. Data were analyzed by ANOVA, for the effect of treatment, time, and period (anxiety pre and post, diurnal pre and post). The TT proved to be stressful for horses. There was a main effect of time (P = 0.0283) on cortisol concentrations, whereby, horses had greater concentrations at the conclusion (93.2 [72.7, 119.5] ng/mL) of the 15 min. There was a tendency for TRT to have lower cortisol concentrations across time points compared to CON (P = 0.0711; 61.3 [48.4, 77.6] ng/mL vs 81.1 [67.5, 97.6] ng/mL). For the ST, TRT horses tended to have longer times to travel 10’ than CON horses (1.35 [0.39,4.70] vs. 0.26 [0.07, 0.91 sec, P=0.064) while not traveling different distances (20±4 vs 21±4 ft, P>0.9). Addition of this supplement to equine rations could have positive benefits for human safety during the training process.