Transitionally it is assumed that sows require a constant amount of amino acids during pregnancy, but there are some who feel that the sows requirements for amino acids change as the sows body changes during different stages of pregnancy. This study tries to pin point the sows requirements for amino acids used in early and late gestation, lactation and for maintenance. The sows were fitted with venous catheter and blood was regularly sampled to determine some specific AA requirements in early and late gestation. In all experiments, energy retention was greater in early gestation than in late gestation, where negative energy retention was observed especially in younger sows. A further study was set up to determine limited amino acids by setting up 5 diets, the first with all essential AA’s and then each after that had one AA removed. These experiments showed that AA and energy requirements of pregnant sows were greater in late gestation than in early gestation so that phase feeding sows different diets and feed amounts in early gestation and late gestation is necessary, the 84th day of pregnancy is recommend as the time to change diets. Increased litter size can increase the amount of milk needed to feed the piglets and this changes as the pigs grow, this can increase the amount of lysine required by the sows to help produce milk. Phase feeding is recommended to accommodate that changing AA requirements in the sow.