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 (Sorex araneus) was measured by two techniques, indirect calorimetry (IC) and the doubly labeled water (DLW) method. Daily energy expenditure (DEE) did not increase significantly 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 during 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 greater than the cost of pregnancy. After the initial increase the maternal DEE, measured by DLW, remained remarkably constant throughout lactation (days 08, 154.3 kJ · d⁻¹; days 9-16, 158.9 kJ · d⁻¹; days 17-23, 181.5 kJ · d⁻¹), although food intake continued to increase. There may be further metabolic compensation during lactation. During both pregnancy and lactation there was a discrepancy between measurements of energy expenditure obtained by the two techniques. In pregnancy the higher DLW expenditures were attributed to a difference in environmental conditions. During lactation we conclude that the high DLW energy expenditures may have in part been due to an exchange of unlabeled CO₂ from the litter to the mother.