Part 3: The third part of the study will occur after the infant has a surgery to reconnect the bowel and remove the ostomy. A spot urine sample will be obtained prior to the stable isotope infusion to ensure that isotope previously consumed/infused will not be considered in the data analysis for this part of the study. The stable isotope study will occur whenever the infant's bowel has been reconnected and the infant has achieved a steady volume and concentration of feedings per kg (minimum of 100 cc/kg/day) for at least 2 days. This volume will continue throughout the first 24 hours of the sample collection period. Infants may be receiving either breast milk (fortified or unfortified) or infant formula. If the infant is receiving breast milk, a 10mL sample of breast milk will be obtained to determine zinc and copper content. Zinc and copper contents of infant formula will be determined from published tables by the manufacturer.