['Feeding and systemic hypoxia are major stresses inducing necrotizing enterocolitis (NEC). This study aims to investigate the role of systemic hypoxia in NEC and its effect before and after feeding.', 'Neonatal mice were studied in three groups. Control (N\xa0=\xa09): breast feeding; NEC A (N\xa0=\xa08), gavage feeding\xa0+\xa0lipopolysaccharide (LPS)\xa0+\xa0preprandial hypoxia; and NEC B (N\xa0=\xa09), feeding\xa0+\xa0LPS\xa0+\xa0postprandial hypoxia. Pimonidazole, a hypoxia marker, was injected intraperitoneally before ileum was harvested for histology and quantitative RT-PCR studies. Statistical analysis was done using the ANOVA and Chi-square test.', 'NEC incidence was 62.5% in NEC A and 88.9% in NEC B. The mortality in NEC B (55.6%) but not A (25%) is significantly higher than control (0%, p\xa0<\xa00.05). Pimonidazole staining elevated in both NEC A and B with higher pimonidazole grade in NEC B (p\xa0<\xa00.01). Both NEC groups had increased the expression of hypoxia-related genes: HIF-1α, GLUT-1, and PHD-3 with GLUT-1 expressed more in NEC B compared with NEC A (p\xa0<\xa00.01). The inflammation marker, IL6, was similarly raised in both NEC A and B.'] Do formula feeding and systemic hypoxia synergistically induce intestinal hypoxia in experimental necrotizing enterocolitis?