Characterising an artiodactyl family inhabiting arid habitats by its metabolism: low metabolism and maintenance requirements in camelids

To test whether camelids, as an artiodactyl family, are characterised by comparatively low energy expenditure, we collated literature data from experiments where at least one camelid and one ruminant species received the same diet, and literature data on camelid metabolism and energy requirements. Additionally, we measured the maintenance and resting metabolism in five alpacas, six llamas and five Bactrian camels by chamber respirometry. Irrespective of whether dry matter intake was expressed as g kg−0.75 day−1, g kg−0.9 day−1, or g kg−1.0 day−1, camelids ingested significantly less food than domestic ruminants (data available for sheep and goats). Although metabolic rates and energy requirements reported for camelids vary over a large range, they are generally below the ‘average’ basal mammal metabolism, and below published energy requirements for ruminants. The mean metabolic rates measured in this study were 215 ± 68, 261 ± 33 and 248 ± 51 kJ kg−0.75 day−1 for alpacas, llamas and Bactrian camels, respectively. The corresponding resting metabolic rates averaged at 144 ± 64, 164 ± 38 and 192 ± 48 kJ kg−0.75 day−1. These findings confirm that camelids in general are characterised by relatively low metabolism and food intake, which might explain why this previously diverse group is currently limited to arid environments with low food resources where a reduced metabolism represents an advantage