Energy expenditure in European roe deer fawns during the suckling period and its relationship with maternal reproductive cost
We measured energy expenditure by means of indirect calorimetry in European roe deer (Capreolus capreolus) fawns at frequent intervals from birth to 45 days of age. Mean resting metabolic rate (RMR) and body mass (BM) did not differ significantly between males (N = 9) and females (N = 14). RMR significantly increased with the fawn age following the equation RMR (kJ·d-1) = 956 + 31.4 age (days). Growth in BM was linear: BM (kg) = 1.565 + 0.135 age (days). Mass-specific RMR decreased from a peak value of ca. 500 kJ·kg-1·d-1 in the first week to 290.4 ± 10.0 kJ·kg-1·d-1 in the sixth week. Concomitant metabolic trials performed with 14 lactating females and their 19 fawns indicated that metabolic weaning began in the third week, when the fawn's energy expenditure became markedly higher than could be compensated for by the mother's milk. Comparison of the energy expenditure of singletons and twins showed that female roe deer are energetically well adapted to nurse two fawns.