Heat loss regulation: role of appendages and torso in the deer mouse and the white rabbit

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Abstract
Summary Thermal conductance was subdivided into the component conductances of the appendages and torso using a heat transfer analysis for the deer mouse,Peromyscus maniculatus, and the white rabbit,Oryctolagus cuniculus. Our analysis was based on laboratory measurements of skin temperature and respiratory gas exchange made between air temperatures of 8 and 34°C for the deer mouse, and from published data for the white rabbit. Two series conductances to heat transfer for each appendage and torso were evaluated: (1) internal (h in), for blood flow and tissue conduction to the skin surface, and (2) external (h ex), for heat loss from the skin surface to the environment. These two series conductances were represented in a single, total conductance (h tot). The limit toh tot was set byh ex and was reached by the torsoh tot of both animals. The increase in torsoh tot observed with air temperature for the mouse suggests that a pilomotor change in fur depth occurred. A control ofh tot below the limit set byh ex was achieved by theh in of each appendage. Elevation of mouse thermal conductance (C) resulted from increases in feet, tail, and torsoh tot. In contrast, the rabbit showed no change in torsoh tot between 5 and 30°C and earh tot exclusively increasedC over these air temperatures. We suggest that the hyperthermia reported for the rabbit at 35°C resulted fromC reaching the physical limit set by torso and nearh ex. Thus the ear alone adjusted rabbitC, whereas the feet, tail, and the torso contributed to the adjustment of mouseC.