KLEIBEB 



TEMPERATURE AND FOOD UTILIZATION 



An animal that is producing flesh or other forms of animal 

 product invariably has a higl^er metabolic rate than a non-produc- 

 ing and especially a fasting animal would have. The difference in 

 heat production between the fed and the fasting animal is called 

 the "heat increment", or the calorigenic effect of food, or the 

 specific dynamic effect of food, an intriguing name considering 

 the fact that the effect is neither specific nor dynamic. 



This calorigenic effect of food intake means a relief to the 

 animal in its fight against a cold environment and an extra burden 

 in the regulation against overheating. 



The situation is illustrated in Figure 20. At a low environ- 

 mental temperature the metabolic rate, being determined by the heat 

 requirement, will be the same for fed and fasting animals. There is 

 thus no calorigenic effect of the food. At this low environmental tem- 

 perature the extra heat for thermostatic control is now less because 

 the minimum heat production of the fed animal is higher than that of 

 the fasting animal.and the calorigenic effect of the food helps to heat 

 the animal. The critical temperature of the fed animal (Tcf) for 

 that reason is lower than that of the fasting animal (Too). Between 

 these two temperatures the calorigenic effect of the food in- 

 creases from zero to C in proportion to the increase in environ- 

 mental temperature. Rubner called the description of this effect 

 his compensation theory. The calorigenic effect compensates for 

 the thermostatic rise in heat production of the fasting animal. 



Above the critical temperature of the fasting animal, the 

 calorigenic effect of the food is independent of changes in environ- 

 mental temperature. The excess heat of the fed animal is greater 

 than that of the fasting animal. This means an extra burden in 

 the fight against overheating. If this burden becomes significant, 

 it affects the food intake. At a sufficiently high environmental 



274 



