Some aspects of thermoregulation in newborn reindeer calves (Rangifer tarandus tarandus).

At birth reindeer calves often are exposed to sub-zero ambient temperatures (Ta) sometimes even combined with wind and precipitation. The resting metabolism was measured in three different age groups (1, 7 and 14 days old) at Ta's of -20, -5, 10 and 20 degrees C. Resting metabolism in the thermoneutral zone decreased from 5.1 W X kg-1 at day 1 and 7 to 4.8 W X kg-1 at day 14. At day 1 apparent lower critical temperature (Tlc) was 11 degrees C, while at day 7 it was 7.7 degrees C and at day 14 7.3 degrees C, but total body conductance continued to decrease below apparent Tlc. At Ta's of -5 and -20 degrees C total body conductance was: 0.77 and 0.72 W X degrees C-1 at day 1, 0.98 and 0.92 W X degrees C-1 at day 7, 1.08 and 0.91 W X degrees C-1 at day 14, respectively. Thermal conductance of pelt samples from the trunk was determined in vitro at different combinations of windspeed, Ta and wetness. The conductance of dry fur increased from 5.9 to 11.8 W X m-2 X degrees C-1 at a windspeed of 0 and 10 m X s-1, respectively, as compared to 28.7 W X m-2 X degrees C-1 when wetted without wind. Newborn reindeer calves seem to be heavily dependent on non-shivering thermogenesis in brown adipose tissue for their cold defence since deep body temperature in a calf subjected to propranolol infusion when exposed to a Ta of -25 degrees C in combination with a 10 m X s-1 windspeed increased its cooling rate five times.