Expert: Florence M Rollwagen - 5/7/2008

Question
an organism needs to eat to make up for the extra energy required to keep the system in the thermoneutral zone during cold seasons. this implies extra feeding. but will the animal need to eat more to off-set the effects of high temperature seeing as how it will take more energy to say, cause vaso-dilation to increase blood supply to the skin to make the blood lose some heat? some books say feed intake decreases in the hot season.

Answer
Hi Joseph and thanks for your question.

It is true that the majority of the calories that we eat are used to maintain body temperature.  Cooling the body is less energy dependent than heating, since cooling follows the second law of thermodynamics.  Vasodilation is passive, and doesn't use much energy.  Sweating, a major mechanism to reduce body heat is also relatively passive.  Activity also slows down in hot weather (think of "siesta' in tropical zones).  This reduction in activity also reduces calorie demand because of less movement.

Here's a link to a graph you can use.
http://www.deer.rr.ualberta.ca/library/deernutr/Nutrition1.gif

I hope this answer has helped you.  Please write back if you have more questions.

FM Rollwagen, PhD