The Control of Panting and Sweating in the Black Bedouin Goat: A Comparison of Two Modes of Imposing a Heat Load

Abstract

The black Bedouin goat uses both panting and sweating as modes of evaporative heat loss. The control of panting and sweating was studied by examining the body temperature distribution under heat loads which produced equivalent levels of evaporative heat loss, namely, solar radiation and high air temperature conditions. Heat exposure induced by high air temperature resulted in a proportionally greater respiratory water loss than did outdoor exposure to solar radiation; the greater respiratory cooling was related to higher hypothalamic and arterial temperatures but lower skin temperatures. However, solar radiation resulted in a higher temperature of the skin under the irradiated fur, and this was associated with a greater cutaneous moisture loss. Thus, the mode of evaporation was concluded to be appropriate to the thermal stimulus: higher nasal temperature resulted in a predominant panting response, and high skin temperature invoked greater sweating. The gradient between arterial and hypothalamic temperature was not necessarily correlated with panting, providing evidence that blood flow through the countercurrent heat exchanger, the carotid rete mirabile, was utilized only when hypothalamic temperature rose above a critical level.