The Effects of Loose Group versus Individual Stall Transport on Glucocorticosteriods and Dehydroepiandrosterone in Yearling Horses

The European Union recently published regulations regarding the welfare of horses during transport, requiring that horses be transported in individual stalls. The objective of this study was to determine whether concentrations of cortisol, corticosterone, or dehydroepiandrosterone (DHEA) differed among horses transported in individual stalls versus in loose groups. A total of 20 yearlings that were regularly handled and accustomed to being tied, but were naïve to transport, were assigned to be transported for 6 hours in either individual stalls or a loose group. The experiment was replicated with a second trial 35 days later following a switchback design. Jugular blood samples were analyzed for plasma cortisol, corticosterone, and DHEA concentrations at pretransport, after 2, 4, and 6 hours of transport, and at 2 and 4 hours after unloading. The data were analyzed using a mixed model repeated measures analysis of variance for treatment effects, whereas differences between sample times within each trial, and pretransport concentrations between trials, were analyzed using paired T-tests. No significant differences were found between treatment groups in concentrations of cortisol (P = .713), corticosterone (P = .370), or DHEA (P = .416). Cortisol and corticosterone concentrations increased significantly during transport, and returned to pretransport concentrations by 2 hours post-transport (P < .01). Changes in concentrations of cortisol and corticosterone indicated that transportation was a significant stressor; however, being transported in a loose group versus individual stalls was not different for these horses.