Abstract: Limits to SusEI during peak lactation may be imposed peripherally by the capacity of mammary glands to produce milk or may be driven by the ability of animals to dissipate body heat. To distinguish between the two mechanisms, body mass change, resting metabolic rate, food intake, litter size and mass were measured in Eothenomys miletus lactating at 5℃, 23℃ and 30℃. The results showed that female E. miletus lactating at 5℃ showed significantly lower change in body mass, but it had higher RMR and food intake than females at 23℃ and 30℃. No significant differences in litter size were observed between the three groups, however, litter mass at 5℃ was lower than litter mass at 23℃ and 30℃. These data suggested that females lactating at cold temperatures increased food intake to compensate for additional energy demands for thermogenesis, but they might not be capable of exporting more energy as milk to the pups, indicating a possible consistency with the peripheral hypothes

Key words: Eothenomys miletus, sustainable energy intake, temperature