This study aims to determine the requirement for Threonine in early and late gestation in sows. The THR requirement in early (25-55d) and late (80-111d) gestation was determined by indicator amino acid oxidation in eight sows fed THR from 20 % to 120 % and from 60 % to 180 % of NRC (1998) estimated requirements in early and late gestation, respectively. L [1-13C]phenylalanine was given orally in eight ½-hourly meals as indicator AA and expired 13CO2 was quantified. The nonlinear Mixed model in SAS was used to determine the THR requirement for each period by breakpoint analysis. Sows responded differently to increasing levels of dietary THR in early and late gestation. Breakpoint analysis resulted in a THR requirement of 4.9 g/d in early gestation (R2=0.71) and 12.3 g/d in late gestation (R2=0.58). The current recommended THR intake during gestation is 10 g/d. These results support previously reported data that there is a greater than 2-fold increase in THR requirement in late gestation. Reducing AA content in sow diets up to 80 d gestation followed by higher AA content in late gestation may substantially reduce feed costs. Phase feeding during gestation may also improve sow reproductive performance by more closely meeting AA demand in late gestation. Current practices of feeding a single AA level during gestation results in negative impacts on sow body condition in late gestation due to deficient AA intake.