Energetic Constraints During Lactation in Mammalian Systems

Lactation represents one of the most energetically demanding phases in the life history of mammals. During this period, females must elevate food intake and metabolic rate to supply sufficient nutrients and energy for milk synthesis, while still maintaining homeostasis. Energy partitioning involves basal maintenance costs, specific dynamic action associated with digestion, and the energetic expense of milk production. A central concept is that of sustained energy intake (SusEI), which denotes the highest level of energy consumption an animal can maintain over the peak lactation period. Multiple physiological and environmental factors interact to define this limit. In particular, the heat dissipation limit hypothesis posits that the capacity to offload excess metabolic heat places a ceiling on energy throughput; when heat cannot be efficiently shed, mothers reduce food intake or milk output to avoid hyperthermia. Morphological traits (such as fur density, body size and vascularisation), behavioural adaptations (nesting and grooming) and ambient conditions all influence heat balance. The interplay of these factors varies among small laboratory rodents, wild rodents, carnivores and ungulates, but the underlying trade-offs between energy acquisition, heat management and reproduction remain universal. Understanding these constraints has implications for wildlife conservation, livestock breeding and human maternal health, as it informs how animals adapt to climate change, nutritional stress and evolving reproductive demands.

Research from Nature Portfolio

Recent studies have investigated the determinants of SusEI and the role of heat dissipation under controlled laboratory conditions. One investigation monitored body temperature and feeding behaviour in lactating mice fitted with implantable sensors; results demonstrated that metabolic heat production rather than heat retention around suckling sites correlates most strongly with peak body temperature, suggesting internal thermogenesis of milk production drives the upper limit of energy intake. A complementary study exposed Swiss mice to thermoneutral conditions and revealed that mothers lactating at higher ambient temperatures exhibited lower food consumption, reduced milk energy output and diminished resting metabolic rate, independent of litter size. This work confirms that, under warmer environments, the limiting factor shifts from mammary synthetic capacity to the female’s ability to dissipate surplus metabolic heat, thereby constraining reproductive performance.

Energetic Constraints During Lactation in Mammalian Systems publication trend

The graph below shows the total number of articles in energetic constraints during lactation in mammalian systems across all publications each year (not limited to Nature Index journals).

Technical terms

Sustained energy intake (SusEI): the maximum rate of energy consumption maintained over prolonged lactation.

Specific dynamic action (SDA): the elevation in metabolic rate required for digestion, absorption and assimilation of nutrients.

Heat dissipation limit (HDL): the concept that an animal’s capacity to release metabolic heat constrains peak energy throughput during lactation.

Resting metabolic rate (RMR): the baseline energy expenditure of an animal at rest and in a post‐absorptive state under neutral thermal conditions.

References

1. Limits to sustained energy intake XXIV: impact of suckling behaviour on the body temperatures of lactating female mice. Scientific Reports (2016).
2. Limits to sustained energy intake XXV: milk energy output and thermogenesis in Swiss mice lactating at thermoneutrality. Scientific Reports (2016).
3. Ambient temperature affects postnatal litter size reduction in golden hamsters. Frontiers in Zoology (2016).
4. Dorsal shaving affects concentrations of faecal cortisol metabolites in lactating golden hamsters. The Science of Nature (2018).
5. Fur removal promotes an earlier expression of involution-related genes in mammary gland of lactating mice. Journal of Comparative Physiology B (2023).