Estimation of energy expenditure in free-living red deer (Cervus elaphus) with the doubly-labelled water method

Energy expenditure was estimated using the doubly-labelled water (DLW) method in summer in five free-living adult, non-pregnant, non-lactating, red deer (Cervus elaphus) hinds (weight 107.3 (sE 0.9) kg; age 6 (sE 1) years) on lowland pasture under typical farming conditions. Climatic I; conditions were monitored throughout the experiment. Errors due to H-2 losses in CH4 and faeces were calculated from previous estimates of stoichiometries. CH4 production, fractionated water loss, urinary N and O-2 consumption were estimated using an iterative approach. The water flux (rH(2)O) in these animals consuming only fresh grass was 12 (sE 0.5) kg/d, the CO2 production (rCO(2)) was 1271 (sE 40) litres/d and the mean energy expenditure was 25 (sE 0.8) MJ/d. There were no significant differences in the isotope distribution spaces and flux rates, rH(2)O, rCO(2) or energy expenditure using the multi-point or two-point approaches to calculation. The DLW-derived energy expenditure of 25 MJ/d is approximately 20% higher than the recommended intake of 21 MJ/d for adult hinds kept outdoors (Adam, 1986) and, at 757 kJ/kg(0.75) per d, one third higher than the value of 570 kJ/kg(0.75) per d for stags penned indoors (Key er al. 1984).