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

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Abstract
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 20oC. Resting metabolism in the thermoneutral zone decreased from 5.1 W‐kg‐1 at day 1 and 7 to 4.8 W‐kg‐1 at day 14. At day 1 apparent lower critical temperature (TIc) was 11oC, while at day 7 it was 7.7oC and at day 14 73oC, but total body conductance continued to decrease below apparent TIc. At Ta of – 5 and – 20oC total body conductance was: 0.77 and 0.72 W‐oC‐1 at day 1, 0.98 and 0.92 WoC‐1 at day 7, r.08 and 0.91 WoC‐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‐m‐2‐oC‐1 at a windspeed of o and 10 m s‐1, respectively, as compared to 28.7 Wm‐2oC‐1 when wetted without wind. Newborn reindeer calves seem to be heavily dependant 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 – 25oC in combination with a 10 m s‐1 windspeed increased its cooling rate five times.