Inclusion criteria  Infants ≤4 months (prior to weaning) Infants born at term (≥37and ≤42weeks), by uncomplicated normal birth or caesarean section and appropriately grown for gestational age.  Exclusion criteria for study population and controls  Infants who present with pre-existing risk factors for altered intestinal perfusion, among others intrauterine growth restriction, birth asphyxia, exchange transfusion, cyanotic congenital heart disease or polycythemia as these infants are at increased risk of necrotizing enterocolitis. Other congenital malformations (chest and abdomen) and infections (such as HIV, hepatitis B and C) Those who received antibiotics or need endotracheal, feeding or suctioning tubes will also be excluded as these manipulations could result in modification of microbial flora and could have an impact in intestinal development. Participants whose parents/carers cannot speak or understand English will be excluded from the study.