Winter Diets? The Secret Is to Chill the Extremities

ScienceDaily (Dec. 16, 2011) — Large mammals living in temperate climates frequently have difficulty finding food during winter. It is well known that they lower their metabolism at this time but does this represent a mechanism for coping with less food or is it merely a consequence of having less to eat? The puzzle has been solved -- at least for the red deer -- by the group of Walter Arnold at the Research Institute of Wildlife Ecology, University of Veterinary Medicine, Vienna.

The results are published in the Journal of Experimental Biology.

Although the temperate climates of central Europe provide plentiful food in summer, finding enough to eat is much more problematic in winter. Many small mammals avoid the problem by hibernating but this survival strategy is generally not practised by larger animals. With the exception of some bears, large mammals remain fully awake throughout the year, yet they too must reduce their metabolism to cope with the comparative scarcity of food. Red deer, for example, are known to lower their heart rate and to allow their extremities to cool substantially during winter. These changes have been interpreted as a mechanism for conserving energy but could simply reflect the fact that the animals cannot find enough food to eat, as the act of digestion is known to have a direct influence on a ruminant's metabolism.

It is clear that red deer must minimise their energy requirements to be able to survive on little but their own body fat over the long winter season. To understand how they do so, Christopher Turbill and colleagues at the University of Veterinary Medicine, Vienna inserted special transmitters into the reticulum (the foremost part of the stomach) of 15 female red deer and monitored the animals' heart rate and stomach temperature for a period of 18 months, including two winters. The deer lived under near-natural conditions but their food intake was tightly controlled, with the amount and the protein richness determined by the scientists. The air temperature was also recorded and statistical modeling was used to untangle the effects of the various different factors -- including swallowing snow, which naturally led to a rapid and dramatic decrease in stomach temperature -- on the animals' metabolism.

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