Appendix I 
Page A I- 27 
3. co 2 , nh 3 , h 2 o and heat generation 
MEASUREMENTS AT LOW AND HIGH HUMIDITIES 
Introduction to Direct and Indirect Calorimetry 
3.1.1 The Definition and Measurement Techniques of Metabolic Rate 
Calorimetry is used to estimate nutritional requirements of humans and farm livestock and to 
evaluate different foods. It is also a powerful research tool used to study fundamental nutritional 
and physiological life processes, and to evaluate stresses imposed by abnormal or severe 
environments. It is, lastly, used in clinics as a diagnostic tool for the investigation of metabolic 
disorders. 
There are two principle types of animal calorimetry methods, direct and indirect. Direct 
calorimetery is the partitioned measurement of radiant, conductive, convective, and evaporative 
energy expenditure from animals. Indirect calorimetry determines energy expenditure from the 
chemical reactions that happen as oxygen is consumed and carbon dioxide is produced. 
The metabolic rate in homeothermic animals is a function of ambient thermal conditions. 
Measurement of energy expenditure has been a powerful tool to study fundamental physiological 
processes, and to evaluate stresses imposed by abnormal or severe environments. Indirect 
calorimetry involves the measurement of respiratory gaseous exchange (O 2 consumption and 
CO 2 production) to calculate heat production. There are now numerous indirect calorimeters 
around the world (Nienaber et al. 1985; Meo 1989; Mathison et al. 1991), although there are only 
two known laboratories with convective calorimeters, which control air velocity as well as 
temperature. In comparative physiology, the metabolic rate of an animal is defined to be its rate 
of energy consumption, that is, the rate at which it converts chemical energy to heat and external 
work. One reason that the metabolic rate of an animal is significant is that the heat and external 
work exported from the animal reflect quantitatively the overall activity of its physiological 
machinery. Heat, in particular, is liberated by every process in the body that uses energy. Thus, 
the rate of heat production is a reflection of the sum total of the rates of all such processes. Heat 
is always the principal component of the metabolic rate. Therefore, for measurement of heat, the 
device used is called a calorimeter. Heat is one of the most conveniently handled forms of 
energy. 
3.1.2 Direct Measurement of Metabolic Rate - Direct Calorimetry 
An animal’s metabolic rate can be measured in a device called a direct calorimeter, which by 
definition assays the rate at which heat is dissipated from the animal’s body. Direct calorimetery 
is the partitioned measurement of radiant, conductive, convective, and evaporative energy 
expenditure from animals. The name calorimeter is derived from the calorie, a unit of measure 
for heat. Direct calorimeters are technically complex. They are designed to be especially 
accurate, sensitive, and versatile. Antoine Lavoisier used one in the first measurements of animal 
heat production in late 1700's. In his experiment, the animal was surrounded by an ice-filled 
