Cow’s milk-based formulas - such as Enfamil and Similac - make it more likely that premature babies (before 37 full weeks) will suffer from the bowel disease necrotizing enterocolitis (NEC). NEC typically develops in preemies being fed this formula when they are two-to-six weeks old. Neonatal intensive care units (NICUs) often rely on cow milk formula - which is high in calories - to provide preemies with nutrition and immune support and to help them gain weight. This formula is also used to supplement nutrition for breastfeeding preemies with latching difficulties.