Effect of dehydration on thermoregulation in eland and hartebeest

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Abstract
Thermoregulatory responses to solar radiation in the eland and hartebeest were examined in the natural radiative environment by determining the relationships of sweating and panting to skin and rectal temperatures. For the hydrated eland the thermoregulatory mechanisms of panting and sweating were related to skin and not to rectal temperature, the onset occurring at a threshold skin temperature of 31.2 and 31.38% C, respectively. When dehydrated, panting and sweating were delayed until threshold skin temperature of 35.1 and 35.7.degree. C, respectively, and both were now also related to a rising rectal temperature. In the hartebeest panting was the only regulated thermoregulatory mechanism. When fully hydrated, panting frequency of the hartebeest was related to skin temperature, the onset occurring at 33.4.degree. C. When dehydrated, regulation of panting shifted to a rising rectal temperature, the onset of occurring at a threshold rectal temperature of 39.5.degree. C. During dehydration the sensitivity and magnitude of the panting frequency in both species were enhanced. Apparently peripheral thermal sensitivity in these African antelopes, when hydrated, helps maintain thermal homeostasis in response to increase in the radiative load. When dehydrated, rigid thermal homeostasis is abandoned to conserve water with a resultant hyperthermia. Apparently, in both species the brain is protected from hyperthermia by an enhanced sensitivity of the panting mechanism.

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