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Why Black Goats in Hot Deserts? Effects of Coat Color on Heat Exchanges of Wild and Domestic Goats

Virginia A. Finch, Razi Dmi'el, Raymond Boxman, Amiram Shkolnik and C. Richard Taylor
Physiological Zoology
Vol. 53, No. 1 (Jan., 1980), pp. 19-25
Stable URL: http://www.jstor.org/stable/30155771
Page Count: 7
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Why Black Goats in Hot Deserts? Effects of Coat Color on Heat Exchanges of Wild and Domestic Goats
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Abstract

Black goats are the most abundant domestic animal in the Negev and Sinai deserts. These goats possess a number of complex physiological adaptations for dealing with a hot desert environment. It seemed possible that their black coat might also be an adaptation for this environment, reducing heat gain and the use of water for evaporative cooling. To test this possibility, we compared the rates at which black goats, white goats, and ibex (a wild goat native to the desert) gained heat and evaporated water in a hot desert at midday. Two methods were used simultaneously to calculate the net rate of heat gain by radiation and convection $(\dot{H}_{gain})$ : a "heat balance method" and a "heat flux method." The heat balance method involved measuring rates of heat production, heat storage, and evaporative heat loss. $\dot{H}_{gain}$ is the sum of rates of evaporative heat loss plus heat storage minus metabolic heat production. The heat flux method involved calculating avenues of non-evaporative heat exchange (radiation, conduction, and convection) and adding these to obtain the net heat gain by nonevaporative means. These methods have been used independently in other studies, and we wanted to compare the results when the methods are used simultaneously on the same animal. The two methods for calculating $\dot{H}_{gain}$, gave similar values. The heat flux method has the advantage of demonstrating the relative importance of each avenue of heat exchange; however, the heat balance method is easier to use and more accurate. $\dot{H}_{gain}$ was twice as great in black goats as in white goats or ibex. This additional heat was lost by evaporation. We do not know why the Bedouins have selected black goats, but we conclude it is not because the black color reduces rates of heat gain and the use of water for evaporative cooling in hot deserts.

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