Impact of Oral Phytozen EQ Supplementation on Plasma Cortisol and Behavior Responses of Young Horses Exposed to Stressful Stimuli

Abstract

Calming supplements are common in the equine industry. This study tested the hypothesis that Phytozen EQ, a blend of citrus botanical oils, magnesium, and yeast would reduce startle response as well as reduce behavioral and physiological signs of stress in young (1.5-6 years of age) horses (n = 14) when tied in isolation and when trailered in isolation. During the 59-day trial, horses were assigned to either the control (CON; n = 7) or treatment (PZEN; n = 7) group that received 56 g of Phytozen EQ daily. Horses underwent a 10-minute isolation test on d 30 and a 15 minute individual trailering test on day 52 or 55. For both tests, blood samples were obtained pre, immediately after, and 1-hour post for analysis of plasma cortisol concentrations, which were analyzed by repeated measures ANOVA. On day 59, horses underwent a startle test, for which time to travel 3 m and total distance traveled were recorded. These data were analyzed using a T-test. During trailering, PZEN horses tended to have lower overall geometric mean (lower, upper 95% confidence interval) cortisol concentrations than CON (81 [67, 98] vs. 61 [48, 78] ng/mL; P = .071). For the startle test, PZEN horses tended to have longer geometric mean times to travel 3 m than CON horses (1.35 [0.39, 4.70] vs. 0.26 [0.07, 0.91 seconds, P = 0.064). Other data points were not different between treatments (P > .1). It is possible that this dietary supplement could have beneficial calming effects on horses undergoing trailering or in novel situations.

Keywords: Behavior; Calming supplement; Magnesium; Startle response; Sweet citrus oil.