Partition of heat loss in resting and exercising winter- and summer-insulated reindeer.

Partition of heat loss was performed in resting (standing) and exercising (running; 9.2 km . h-1 for 40 min) winter- (W) and summer- (S) insulated conscious reindeer (Rangifer tarandus tarandus) in a climatic chamber set to an ambient temperature (Ta) of -30, 0, or 25 degrees C. Heat loss and production were determined using indirect calorimetry. The relative importance of radiant heat loss was greatest during rest at low Ta's, both during winter and summer (44-58% at Ta's -30 and 0 degrees C). At high Ta's, especially during exercise, a large proportion of total heat loss occurred through evaporation [45% at Ta 25 degrees C during rest and 47% at Ta 0 degrees C during exercise (W); 38% at Ta 25 degrees C during exercise (S)]. The proportion of heat lost through convection during rest and exercise was 38-52 and 46-72%, respectively, depending on Ta and season. The legs were found to represent an important avenue for radiant heat loss, particularly in heat stress situations. Their importance for convective heat loss was even greater, especially during exercise.