THE EFFECT OF ORIENTATION DURING TRAILER TRANSPORT ON HEART-RATE, CORTISOL AND BALANCE IN HORSES

Sixteen same-sex pairs of Quarter Horse and Quarter Horse-cross yearli ngs (eight pairs during each of two trials, 1 year apart) were transpo rted for 17.8 +/- 0.52 min over a standard course with one horse facin g in the direction of travel and one facing the opposite direction. Th e orientation of the horses in each trial was alternated with respect to the side of the trailer (float). Heart rates were monitored continu ously using a strip chart recorder and were determined for the followi ng events during each trip: (1) after the horses were loaded, but just prior to beginning the trip; (2) immediately after the initial moveme nt of the trailer; (3) during travel over smooth roads near the start and near the end of the trip; (4) before and after an abrupt stop; (5) the mean for the entire trip. During the second trial, plasma concent rations of cortisol and thyroxine (T4) were determined in blood sample s taken via jugular puncture in the holding paddock prior to any handl ing beyond catching, in the trailer prior to hauling and in the traile r immediately after the trip. Observers riding inside the trailer reco rded how often the horses impacted the sides and ends of the trailer, lost their balance, pawed, vocalized or defecated. Rear facing horses had fewer side and total impacts and losses of balance (P < 0.05), and thus were better able to maintain their balance during trailering. Or ientation, side of trailer and gender had no significant effect on any of the heart rates or log transformations of hormone concentrations; however, trailering increased cortisol (P < 0.005) and heart rates (P < 0.001) overall. All horses' heart rates gradually decreased during t he course of the trip. The general stress response elicited by trailer ing may have masked any treatment effects on heart rate and cortisol. Having horses face away from the direction of travel appears advantage ous because of their improved ability to maintain their balance.