Energy expenditure of free-living reindeer [Rangifer tarandus tarandus] estimated by the doubly labelled water method
2000
Gotaas, G. (Tromsoe Univ., (Norway). Dept. of Arctic Biology and Inst. of Medical Biology) | Milne, E. | Haggarty, P. | Tyler, N.J.C.
The doubly labelled water (DLW) method was used to measure total energy expenditure (TEE) in three male reindeer (Rangifer tarandus tarandus) aged 22 months in winter (February) while the animals were living unrestricted at natural mountain pasture in northern Norway (69 deg 20'N). The concentrations of sup2 H and sup18 O were measured in water extracted from samples of faeces collected from the animals 0.4 and 11.2 days after injection of the isotopes. Calculated rates of water flux and CO2-production were adjusted to compensate for estimated losses of sup2 H in faecal solids and in methane produced by microbial fermentation of forage in the rumen. The mean specific TEE in the three animals was 3.057 WúkgE-1 (range 2.436 - 3.728 WúkgE-1 ). This value is 64% higher than TEE measured by the DLW method in four captive, non-pregnant adult female reindeer in winter and probably mainly reflects higher levels of locomotor activity in the free-living animals. Previous estimates of TEE in free-living Rangifer in winter based on factorial models range from 3.038 WúkgE-1 in female woodland caribou (R. t. caribou) to 1.813 WúkgE-1 in female Svalbard reindeer (R. t. platyrhynchus). Thus, it seems that existing factorial models are unlikely to overestimate TEE in reindeer/caribou: they may, instead, be unduly conservative. While the present study serves as a general validation of the factorial approach, we suggest that the route to progress in the understanding of field energetics in wild ungulates is via application of the DLW method.
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