The roles of body mass and gravity in determining the energy requirements of homoiotherms.

Studies by Kleiber and by Brody in the 1930's established the 3/4 power of body weight as the unit for comparison of metabolic phenomena in homoiotherms. Later Kleiber conceived of the energy requirement as a composite function, with a thermoregulatory component, proportional to heat loss, and an antigravity component that is directly proportional to body weight. Maintenance feed requirements have been measured with groups of small animals chronically exposed to several acceleration fields. Analysis of the results leads to an arithmetic relationship between the maintenance requirement and acceleration field strength: Fg = Fo+k g Where: F is the maintenance feed requirement (Fg in field of g strength, and Fo where g=0); and, g is the ambient acceleration field strength. When the equations are compared for groups of different body size, Fo tends to vary between the 0.4 and 0.5 power of body mass--and k tends to be the same, irrespective of body mass (BM). These findings tend to confirm the Kleiber concept of a composite nature of homoiotherm maintenance requirements.