Postnatal changes in the body composition components, namely, body water, fat-free dry solids, and fat, were determined for laboratory-maintained brown lemmings, Lemmus sibiricus. The proportion of body water decreased while the proportion of fat-free dry solids and fat increased from birth to approximately 15 weeks of age. From 20 through 80 weeks of age, the proportions of all body composition components as well as total body weight remained relatively constant. Body composition components were more closely correlated with body weight than with chronologic age. As a function of body weight, body water decreased while fat-free dry solids and fat increased. Body fat was the most variable body composition component as related both to body weight and chronologic age. The von Bertalanffy growth equation and the differential growth equation were used to describe the body composition component data as related to chronologic age and body weight, respectively.
