The structure and insulation properties of the reindeer fur

1. The structure of the fur of the reindeer (6 adults, 4 calves) was studied with light and scanning electron microscopy and skin and rectal temperatures were measured in 216 living animals at varying ambient temperatures (−28 to +15°C) and also on excised skin samples in the laboratory (temperature range −20 to +20°C, wind 0 or 10m/sec, 5 different directions). 2. Guard hair count and length varied according to the site of excision and were on average 2000/cm2 and 12mm on the foreleg, 1000/cm2 and 30mm on the abdomen and 1700/cm2 and 30mm on the back. The corresponding counts in the calves were higher but the hairs were shorter. 3. The rectal temperatures ranged from 38 to 40°C independently of the ambient temperature. 4. The dependence of the skin temperature on the ambient temperature was complex in living animals. The dependence was strongest in the legs. 5. The skin temperature of the excised samples depended rather linearly on the ambient temperature. 6. It is concluded that the reindeer can maintain its body temperature also in severe cold although the extremities show characteristics of heterothermia.