EFFECTS OF DEHYDRATION ON THERMOREGULATORY RESPONSES OF HORSES DURINGLOW-INTENSITY EXERCISE

Effects of dehydration on thermoregulatory and metabolic responses wer e studied in six horses during 40 min of exercise eliciting approximat ely 40% of maximal O2 consumption and for 30 min after exercise. Horse s were exercised while euhydrated (C), 4 h after administration of fur osemide (FDH; 1.0 mg/kg iv) to induce isotonic dehydration, and after 30 h without water (DDH) to induce hypertonic dehydration. Cardiac out put was significantly lower in FDH (144.1 +/- 8.0 l/min) and in DDH (1 56.6 +/- 6.9 l/min) than in C (173.1 +/- 6.2 l/min) after 30 min of ex ercise. When DDH, FDH, and C values were compared, dehydration resulte d in higher temperatures in the middle gluteal muscle (41.9 +/- 0.3, 4 1.1 +/- 0.2, and 40.6 +/- 0.2-degrees-C, respectively) and pulmonary a rtery (40.8 +/- 0.3, 40.1 +/- 0.2, and 39.7 +/- 0.2-degrees-C, respect ively). Temperatures in the superficial thoracic vein and subcutaneous sites on the neck and back and peak sweating rates on the neck and ba ck were not significantly different in DDH and C. In view of higher co re temperatures during exercise after dehydration and decreases in car diac output without concomitant increases in peripheral temperatures o r reduced sweating rates, we conclude that the impairment of thermoreg ulation was primarily due to decreased transfer of heat from core to p eriphery.