Abstract: Females in mammals appeared to approach an upper limit to the rate of sustained energy intake/metabolic rate (SusEI/MR) during lactation. However, different species of animals may respond differently to the sustainable limit. Here, the energy metabolism was measured during lactation in female Eothenomys miletus raising litters of natural size (Con), and females whose litter size was manipulated during early lactation to support fewer or more pups (minus pups, MP or plus pups, PP). E. miletus significantly decreased their body mass and increased food intake from early to late lactation， and MP females had lower food intake than the control and PP females. Litter size of the PP group decreased significantly over the period of lactation, and pups were weaned at similar weight to that of the controls. MP females supported a significantly lower litter mass throughout lactation compared with the control and PP females, but during late lactation the pups from the MP group were significantly heavier. Resting metabolic rate (RMR) did not differ significantly between the three groups and the energy intake during peak lactation was 3.56, 3.36 and 3.64 RMR for the control, MP and PP females, respectively. All of the results suggested that female E. miletus reached a plateau in food intake at around 12 g/d during peak lactation, which might signify a limit of SusEI at 3.6×RMR.

Key words: Eothenomys miletus, sustainable energy intake, litter size