THE ENERGETICS OF REPRODUCTION IN THE COMMON SHREW (SOREX-ARANEUS) - A COMPARISON OF INDIRECT CALORIMETRY AND THE DOUBLY LABELED WATER METHOD

Energy expenditure of the common shrew (Sorer araneus) was measured by two techniques, indirect calorimetry (IC) and the doubly labeled wate r (DLW) method. Daily energy expenditure (DEE) did not increase signif icantly during pregnancy when measured by IC (days 0-7, 56.5 kJ.d(-1); days 8-14, 60.8 kJ.d(-1); days 15-20, 65.0 kJ.d(-1)) or when measured by DLW (days 0-7, 70.1 kJ.d(-1); days 8-14, 72.6 kJ.d(-1); days 15-20 , 74.9 kJ.d(-1)). Food intake also did not increase significantly duri ng pregnancy. We hypothesize that there was a decrease in a component of the energy budget not directly associated with reproduction, termed metabolic compensation The energetic cost of lactation was far greate r than the cost of pregnancy. After the initial increase the maternal DEE, measured by DLW remained remark ably constant throughout lactatio n (days 0-8, 154.3 kJ.d(-1); days 9-16, 158.9 kJ.d(-1); days 17-23, 18 1.5 kJ.d(-1)), although food intake continued to increase. There may b e further metabolic compensation during lactation. During both pregnan cy and lactation there was a discrepancy between measurements of energ y expenditure obtained by the two techniques. In pregnancy the higher DLW expenditures were attributed to a difference in environmental cond itions. During lactation we conclude that the high DLW energy expendit ures may have in part been due to an exchange of unlabeled CO2 from th e litter to the mother.