EVAPORATIVE WATER-LOSS - THERMOREGULATORY REQUIREMENTS AND MEASUREMENTS IN THE DEER MOUSE AND WHITE-RABBIT

Using a physical model of the capacity for non-evaporative heat loss and measurements of metabolic heat production, the evaporative requirements for thermoregulation in the deer mouse, P. maniculatus, and the white rabbit, O. cuniculus were evaluated. The physical limit to non-evaporative heat loss was calculated from the heat transfer properties of the 2 animals and expressed as a maximum thermal conductance (Cmax). Two physiologically-based thermal conductances were derived from evaporative water loss, respiratory gas exchange and core temperature measurements made between 8.degree.-34.degree. C on the deer mouse, and taken from published data for the white rabbit. The thermal conductance for nonevaporative heat loss (C) was calculated from net heat production, whereas Cm represented the thermal conductance required to dissipate metabolic heat production. Evaporation is required when metabolic heat production exceeds the capacity for non-evaporative heat loss (as shown by Cm > Cmax). Evaporation increased in both animals although additional capacity to lose heat remained (i.e., C < Cmax). Evaporation increased with C above 30.degree. C for the mouse and at each 5.degree. C measurement interval from 15.degree.-30.degree. C for the rabbit. Evaporation was greater than that required for thermoregulation for both animals as determined from a physical model of heat loss because both evaporation and C increased together to regulate heat loss.