Soybean meal (SBM) is an important protein source in swine diets, but inclusion is sometimes reduced and SBM is partially replaced with synthetic amino acids (AA) because this may sometimes reduce diet costs. Over the past few decades, reproductive efficiency in sows has improved significantly, due to genetic selection, resulting in litters that can exceed 20 piglets. This increase in prolificacy has, therefore, increased the metabolic demands for AA and energy during both gestation and lactation. Adequate energy intake in gestation supports fetal growth and mammary development, but excessive energy intake during gestation may reduce feed intake during lactation, which has a negative effect on milk production. Likewise, high protein intake during gestation will improve milk production, protein accretion, and litter and pig weight at weaning, but it may also lead to an increase in fat accretion rather than protein accretion in gestating sows.