• horse;
  • thermoregulation;
  • exercise;
  • sweating;
  • temperature


Previously we have observed a decline in sweating rate (SR) during high intensity exercise in an incremental test protocol. In man, the sweating sensitivity (SR/°C) has been shown to vary with exercise intensity. The aim of the present study was to determine if thermoregulatory responses in the horse, a prolific sweater with a high rate of metabolic heat production, were modified by exercise intensity. The effect of 3 separate exercise intensities (50 (S), 70 (M) and 90% (F) V̇o2Peak on neck (SRN) and gluteal sweating rate (SRG), pulmonary artery (TPA), rectal (TREC) and skin temperatures on the neck (TSK-N) and gluteal region (TSK-G) were investigated. Horses were exercised for ˜2 min at each exercise intensity in a randomised order. The rate of increase in TPA increased with exercise intensity (P<.05) (0.27 ± 0.05, 0.43 ± 0.04 and 0.77 ± 0.05°C/min during S, M and F, respectively. The TPA and TSK temperatures at the onset of sweating were not different between exercise intensities (P>0.05). Despite the increased rate of heat production with increasing exercise intensity, sweating sensitivity decreased on both the neck [(P<.05) (18.2 ± 3.4 (S), 12.0 ± 3.5 (M) and 2.9 ± 0.7 (g/m2/min)/°C (F)] and gluteal region [(P<.05) (8.9 ± 2.0 (S), 5.1 ± 1.7 (M) and 0.8 ± 0.3 (g/m2/min)/°C (F)]. During exercise at 90% V̇o2peak sweating sensitivity and the rate of increase in skin temperature were markedly reduced compared to at 70% V̇o2peak. The present investigation demonstrates that the drive to thermoregulate is overridden during short-term, high-intensity exercise, resulting in greater heat storage (TPA) as a result of a lower SR sensitivity.