BODY WATER AND FAT CONTENT IN THE REDBACK VOLE

It is generally accepted that the metabolic rates of mammals are a function of their body weight (B r o d y, 1945). Recent li terature how-ever, has questioned the use of total body weight on the grounds that certain components of the body do not correlate directly with the meta-bolic rate. M u l d o w n e y (1961) found that body fat contributed very little to the BMR of mamals, and H a y w a r d (1964) working with Peromyscus demonstrated a consistent relationship between metabolic rate and body water content. Neither of these components is known for many wild mammals. The authors have had a special interest in the redback vole, Clethrionomys gapperi loringi ( B a i l e y, 1897), a pro-minet species in the bog ecosystems that they are studying, and felt such measurements would be useful in interpreting energy transfers in this species. Accordingly, 14 C. gapperi captured in the Whiteshell Provincial Park of southeastern Monitoba, Canada, and held in rearing on an artifical diet 1 for a period of 3 months were analysed for body water and fat following standard procedures (A.O.A.C. 1955). The specimens were killed and weighed, then desicated for a week to constant weight in an oven at 90°C. under partial vacuum. The water content was then the difference in weight before and after treatment. The fats were then extracted in ether (b.h. 30°—60°C) in a Soxhlet apparatus for 16 hours at which time constant weight had again been reached. The fat content was then the difference in weight before and af ter extraction. 1 Free water 12.7%, crude protein 18.1%, crude fat 40.0%, crude fiber 3.0%, salt 0.45%, calcium 0.85%. phosphorus 0.65%. zinc 0.008%, nitrate trace, Vitamine