Homeostatic mechanisms that regulate lactation during energetic stress.

Apart from the metabolic differences between species (ruminant vs. nonruminant), there are other important physiologic differences in both the energy requirements for lactation and in the control of milk production between dairy cows and women. Unlike dairy cows, the partitioning of nutrients for lactation in women therefore cannot be generalized to all lactating women but must be related to individual women, taking into account their particular metabolic circumstances. Homeorhetic models may be appropriate for women in developing countries, whereas in developed countries, the flexibility in both homeostatic and homeorhetic adaptations to the substrate demands for milk synthesis means that women can adopt a variety of strategies to support the metabolic demands of lactation. In these women, as in dairy cows, body reserves, dietary intake and milk production vary widely among individuals, and individual differences in capacity for homeorhetic regulation of nutrient partitioning under these conditions require further investigation.