Panting in small mammals: a comparison of two marsupials and the laboratory rabbit.

By use of a barometric technique, tidal volume (VT), minute volume (VE), respiratory frequency (f), and respiratory evaporative heat loss (Eex) were measured from conscious unrestrained potoroos (Potorous tridactylus), barred bandicoots (Perameles gunnii), and New Zealand white rabbits (Oryctolagus cuniculus) at temperatures in and above the thermoneutral zone (TNZ). Rectal temperature (Tre) and oxygen consumption were also measured. VT initially decreased with rising Ta, but in the potoroo and rabbit it then increased past the resting level. VE increased much more in the marsupials than in the rabbit, and higher Eex maxima were also found for the marsupials. The marsupials had high Q10's above the TNZ, and had a panting efficiency of 80%. The rabbits had a Q10 of 1.9 above the TNZ and 100% panting efficiency. The high VE and Eex and low panting efficiency of the marsupials may be due to their lower Tre which allows transfer of heat from the environment to the animal.