Panting in reindeer (Rangifer tarandus)

Two winter-insulated Norwegian reindeer (Rangifer tarandus tarandus) were e xposed to air temperatures of 10, 20, 30, and 38 degrees C while standing a t rest in a climatic chamber. The direction of airflow through nose and mou th, and the total and the nasal minute volumes, respectively, were determin ed during both closed- and open-mouth panting. The animals alternated betwe en closed- and open-mouth panting, but the proportion of open-mouth panting increased with increasing heat load. The shifts from closed- to open-mouth panting were abrupt and always associated with a rise in respiratory frequ ency and respiratory minute volume. During open-mouth panting, the directio n of airflow was bidirectional in both nose and mouth, but only 2.4 +/- (SD ) 1.1% of the air was routed through the nose. Estimates suggest that the p otential for selective brain cooling is markedly reduced during open-mouth panting in reindeer as a consequence of this airflow pattern.