POST EXERCISE CHANGES IN COMPARTMENTAL BODY-TEMPERATURE ACCOMPANYING INTERMITTENT COLD-WATER COOLING IN THE HYPERTHERMIC HORSE

Whereas the efficacy of cold mater cooling of horses has been demonstr ated by several studies, the dynamics of temperature changes within an d between compartments (primarily muscle, blood [core], skin and deep core [recta]) have not been investigated, Changes in body temperature associated with cold water cooling were investigated in the hypertherm ic horse, Muscle (T-MU), pulmonary artery (T-PA), rectal (T-REC), tail -skin (T-TSK) and coat surface (T-COAT) temperatures, were monitored c ontinuously in 5 Thoroughbred horses during and after exercise in hot humid (30 degrees C and 80% RH) conditions on a treadmill, Horses were cooled in the hot humid environment with cold water (similar to 6 deg rees C) for 6 30 s periods, Between each 30 s cooling period the horse s stood for 30 s, A total of 180 l of cold water was applied. Horses w ere monitored for a further 4 min following the final cooling period, From the end of exercise to the end of the final cooling (6.5 min), me an (+/- s.e.) rates of decrease for T-TSK and T-PA were similar (0.8 /- 0.1 and 0.8 +/- 0.1 degrees C/min, respectively), The effects on T- MU and T-REC were less marked, with average rates of 0.2 +/- 0.1 and 0 .0 +/- 0.1 degrees C/min, respectively. During the first 4 min of cool ing, T-PA fell during the 30 s period of water application and rose du ring each 30 s period of standing, When T-PA fell below similar to 36. 5 degrees C, these variations were suppressed and T-PA rose steadily, despite continued applications; T-REC and T-MU continued to fall, alth ough less rapidly than before, These observations are consistent with the onset of skin vasoconstriction at low T-PA. The mechanism is media ted through a cooling of circulating blood volume providing a greater capacity for heat transfer between muscle and circulation. Intermitten t application of cold water (similar to 6 degrees C) improves heat rem oval without apparent deleterious effects and is well tolerated, Even when hypothermia develops (based on T-PA), muscle and rectal temperatu res continue to fall.