Data on energy metabolism and body composition changes of the pregnant and lactating sow have been considered in order to propose methods for determination of energy requirements according to a factorial approach. Daily requirements for maintenance at thermoneutrality amounts to about 105 and 110 kcal ME/kg BW.75 in pregnant and lactating sows, respectively. During pregnancy, maintenance represents 75 to 85% of the total requirements and is affected greatly by environmental temperature and activity of the animals. Requirements for total uterine gain are low, but they increase with advancement of pregnancy. In addition, the daily ME requirements during pregnancy depend on the amount and composition of maternal weight gain and on the previous lactation body weight loss. The factorial approach indicates clearly that daily ME recommendation in pregnant sows varies from 6 to more than 10 Mcal and must be adapted to each sow within a herd. A method for prediction of ME requirements in lactating sows that considers a relatively precise estimate of energy output in milk is proposed. Results indicate that daily ME requirements are particularly high (15 to more than 20 Mcal) and generally are not met by voluntary feed intake. Emphasis also has been given to prediction of body composition changes that occur over the reproductive life of the sow. Data from the factorial approach allow for optimization of sow energy nutrition to ensure a normal evolution of body weight changes and to avoid major changes in body weight and composition. However, no available data demonstrate whether such a strategy is concomitant with optimal lifetime reproductive performance.