Stress responses of horses during a long period of transport in a commercial truck

OBJECTIVES: To characterize progressive patterns of dehydration, stress responses, and water consumption in horses transported long distances in hot weather and to evaluate various measurements in detecting dehydration and stress in transported horses. DESIGN: Prospective study. ANIMALS: 30 mature, healthy horses. PROCEDURE: The following 4 treatment groups were studied: horses that were penned and offered water every 5 hours (n = 5), horses that were penned and not offered water (5), horses that were transported in a truck and offered water every 5 hours (10), and horses that were transported and not offered water (10). The study commenced after 6 hours of water deprivation. Every 4 hours, the truck returned to the pen area and body weights were measured, physical examinations were performed, and blood samples were obtained. During this 1-hour period, water was offered to some horses, depending on treatment group. RESULTS: After 24 hours of transport, 3 horses were judged unable to continue and the study was terminated. Horses that were penned and offered water drank a mean of 38.2 L and horses that were transported and offered water drank 20.9 L, but some of the latter horses did not drink until after 19 or 24 hours of transport. In horses that were transported or penned and not offered water, serum electrolyte concentrations were greater than reference range values by 19 hours. Most horses that were transported and offered water consumed adequate water to postpone severe dehydration beyond 24 hours. CLINICAL IMPLICATIONS: Tame horses in good condition and initially deprived of access of water for approximately 6 hours can be transported in groups in open trailers during hot, humid conditions for up to 24 hours before dehydration and fatigue become severe. Rectal temperature and appearance of the horses were the most useful measures for determining crisis situations.