Reindeer 'pant' to stay cool in their luxurious fur coats
Reindeer avoid overheating during winter when insulated in their luxuriously thick pelts by panting to lower their brain temperature.
While their thick, long coats keep the cold out, they also keep the warmth in - which is fine when the animals are resting, but means they have to release heat when active.
So the animals use a number of tactics to make sure they don't burn up when moving around in the gripping cold of the Arctic, according to scientists.
Thick fur coat: Reindeer avoid overheating during winter by panting to lower their brain temperature
Lead researcher Dr Arnoldus Blix, from the University of Tromso, Norway, trained reindeer to run on treadmills to measure how they keep cool when exerted.
He found that reindeer adapt by using three tactics - panting with their mouths closed to evaporate water from the nose; panting with the mouth open to evaporate water from the tongue; and activating a cooling system that selectively cools the blood supply to the brain.
More...
The scientists monitored reindeer brain temperatures, breathing rates and the blood flow through several major blood vessels in the head.
They found that the animals use th! ree stra tegies to keep cool, but only resort to cooling their brains with a heat exchanger when their temperature becomes dangerously high.
Dr Blix said: 'Reindeer are the best animals to work with; once they trust the trainer they will do anything for you.'
The team trained reindeer to trot at 9km per hour on a treadmill in temperatures from 10 to 30C to get the animals warmed up while they recorded their physiological responses.
Scientists trained reindeer to run on treadmills to measure how they keep cool when exerted
In the early stages of the run their breath rate rocketed from seven breaths per minute to an impressive 260 breaths per minute.
Dr Blix found that the animals were inhaling chilly air through their noses and evaporating water from the mucous membranes to cool blood in the nasal sinuses, before sending it back to the rest of the body through the jugular vein to keep their temperature down.
However, as the reindeer continued exercising and generating more heat, they switched to panting, throwing their mouths wide open and flopping their tongues out like dogs.
'The tongue is large, vascularised and well circulated,' said Dr Blix. 'They moisturise the tongue so you have evaporation which also takes heat away from the blood'.
Monitoring the temperature of the reindeer's brain, the team noticed that the blood flow through the animal's cooling tongue peaked when the brain's temperature reached a critically high 39C, at which point the reindeer switched to their third tactic.
They began selectively cooling the brain by diverting cooled venous blood - which came from the nose - away from the body and up into the head, where it entered a networ! k of hea t exchanging blood vessels to cool the hot arterial blood destined for the brain to protect it from overheating.
Dr Blix said that initially he had not thought that this strategy would work.
He said: 'Only two per cent of the respiratory volume went through the nose when they resorted to open mouth panting0'.
However, when he calculated the colossal amounts of air inhaled by the exercising animals - coupled with the low air temperatures - it was clear that the reindeer were able to inhale sufficient cold air through their noses to keep their brains cool, but only as a last resort once the other cooling tactics were no longer sufficient.
The research is published in The Journal of Experimental Biology.
Comments