Second, a NEC model was established by hypoxia, cold stimulation, artificial feeding and LPS induction to further investigate the effect of B. breve AHC3 on necrotizing enterocolitis in newborn SD rats in vivo, through observing incidence rate of NEC, severity of ileal injury, level of inflammatory factors and expression of iNOS, to provide theoretical basis for clinical application of B. breve AHC3 to prevent and treat NEC. The gene discussed is NOS2; the disease is necrotizing enterocolitis.