Every Christmas, children imagine nine reindeer laboring hard to pull Santa’s heavily loaded sleigh, their dense coats perfect for keeping them warm on the coldest of nights.
A new study from Norway shows that these Arctic mammals, Rangifer tarandus, possess an inherent cooling mechanism to prevent heat stress, even when running at full pelt.
Led by Arnoldus Blix at the University of Tromsø, president of the International Arctic Ungulate Society, a team of researchers has shown how reindeer keep cool while actively working.
Under fully controlled conditions, the scientists trained nine female reindeer to trot at 9 kilometers per hour for 20 minutes on a treadmill.
“Reindeer are the best animals to work with; once they trust the trainer they will do anything for you,” said Blix in a press release.
The temperature was varied from 10 to 30°C (50 to 86°F) and the deer’s physiological responses were recorded. During strenuous workouts, their breathing rates shot from the norm of 7 breaths per minute to 250 per minute, while the brain temperature increased from 38.5 to 39.5°C (101.3 to 103.1°F).
Reindeer have a thick fur coat which prevents body heat from escaping. However, excessive heat generated during workouts can be potentially dangerous for normal metabolic functioning.
The team found that reindeer use three strategies for effective thermal regulation.
During the early stages of the run, the deer panted with their mouths closed, allowing water to evaporate from the nose and cool the blood in the nasal sinuses, before sending it back into the main circulation in the body.
Gradually, they began taking quick breaths with the mouth wide open to enable water evaporation from their flopping tongues for cooling.
“The tongue is large, vascularized and well circulated,” explained Blix. “They moisturize the tongue so you have evaporation which also takes heat away from the blood.”
Finally, the activated vascular cooling system specifically diverted the cooled blood coming from the nose into the head. Here, it mixed with the hot arterial blood supply to the brain and eventually cooled it, keeping the brain temperature under control.
The research paper is published in The Journal of Experimental Biology
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