Body composition of free-ranging wolves (Canis lupus)

We used deuterium water dilution to estimate body composition of free-ranging wolves (Canis lupus L., 1758) in the Nelchina Basin, Alaska. Body mass differed between sexes throughout the year but did not vary within sex. Mean fat mass and mean energy content were highest in both sexes in the spring. Mean lean mass was lowest in both sexes in the spring. Body mass and lean body mass were positively related to animal age in both males and females up to age 6-8 years. There was no relationship between body fat content and animal age in either sex except in older animals. Thus, growth beyond age 2 consists primarily of lean mass. Body mass of reproductively active females was greater than nonreproductively active females in the spring but not in summer or fall. Deuterium should be allowed to circulate in the wolf for at least 120 min to ensure complete equilibration regardless of season, sex, age, or reproductive status.