Sustained energy intake in lactating Swiss mice: a dual modulation process

Area of Science:

• Physiological Ecology
• Reproductive Biology
• Animal Metabolism

Background:

• Sustained energy intake (SusEI) during lactation is crucial for female mammals, balancing energy demands with other physiological needs.
• Previous hypotheses suggested SusEI is limited by either mammary gland milk production capacity (peripheral limitation) or the female's ability to dissipate body heat (heat dissipation).

Purpose of the Study:

• To investigate the combined effects of litter size and ambient temperature on indicators of SusEI and reproductive performance in lactating Swiss mice.
• To determine whether peripheral limitation or heat dissipation is the primary constraint on energy intake under varying environmental conditions.

Main Methods:

• Lactating Swiss mice were subjected to different litter sizes and ambient temperatures (21°C and 30°C).
• Physiological (body temperature, food intake), behavioral, and morphological (mammary gland mass) indicators of SusEI were measured.
• Reproductive performance metrics including pup body mass and survival rate were assessed.

Main Results:

• Energy input, output, and mammary gland mass increased with litter size.
• At higher temperatures (30°C) and large litter sizes, females showed reduced food intake, thermal conductance, and milk energy output, alongside increased body temperature.
• A significant interaction between ambient temperature and litter size constrained females' energy budgets.

Conclusions:

• SusEI during lactation is limited by a combination of mammary gland capacity and heat dissipation.
• Peripheral limitation is more dominant at room temperature, while heat dissipation becomes a more significant factor at warmer temperatures.
• The impact of heat dissipation limits on energy intake is temperature-dependent, decreasing as ambient temperature rises.