Maintenance energy requirements during lactation in rats.

Evidence is presented to support the postulates that increases in apparent maintenance requirements during pregnancy and lactation are due, in part, to increases in relative weights and metabolic activities of vital organs. Rates of glucose, palmitate and pyruvate oxidation per unit weight in vitro were one-and-a-half to three times greater in liver, heart and intestine samples from pregnant and lactating as compared to nonlactating rats. Relative weights of liver, intestinal tract and heart were greater in lactating as compared to nonlactating rats. Weights of liver, heart and intestines are functions of feed intake to apparent maintenance requirements. A theoretical calculation indicated that an increase in maintenance requirements from 100 kcal metabolizable energy/kilograms0.75 to 124 kcal metabolizable energy/kilograms0.75 during lactation in rats could be explained on the basis of changes in the relative weights of liver, intestines and heart.