Thermoregulation in reindeer
Thermoregulation was studied in Finnish reindeer (Rangifer tarandus L) on captive and herded individuals during 1977-85. Newborn calves maintained a high rectal temperature (Tre) (+39 to +41°C) even at —23°C by increasing heat production 5- to 6-fold through non-shivering thermogenesis, stimulated by cold-induced noradrenaline (NA). Plasma NA and thyroxine (T4) were high (18 ng/ml and 459 nmol/1) in neonatal reindeer. Sensitivity to exogenous NA was lost during the first 3-4 weeks of life. At +20°C and above, calves increased Tre (ca 1°C), oxygen consumption and heart rate, thereby showing poor heat tolerance. Thermal conductance was low in a cold environment, but rose sharply as ambient temperature (Ta) increased above + 10°C. The Tre of adults (+ 38 to +39°C) was independent of Ta (—28 to +15°C). Coarse (hollow) hair density and length in adults averaged 2000/cm2 and 12 mm on the legs, 1000/cm3 and 30 mm on the abdomen and 1700/cm2 and 30 mm on the back (calves 3200/cm2, 10 mm), respectively. The dependence of skin temperature on the Ta was linear in excised fur samples, but complex in living animals being strongest in the legs. Serum adrenaline correlated with the weight, age and total lipids. Serum NA and dopamine-fi-hydroxylase were highest in spring and decreased by autumn. Serum T4 was highest in summer and lowest in spring.