The infants will be recruited between birth and 14 days of life and will start on the allocated study formula as soon as they are enrolled. In practice this will tend to be immediately after birth. The treatment period, in terms of data necessary for the primary outcome, will be until they reach 16 weeks old. Growth and other measurements will be collected on five separate occasions during this period, ie 2, 4, 8, 12 and 16 weeks of life. Although the study intervention formally ends at 16 weeks, it will be useful to have a follow up visit at 26 weeks to collect further data on the gut microflora in the sub-group of infants who have already provided a stool sample at 8 weeks. This follow-up visit will be of benefit to the subject as they receive a weight check and clinical examination by a paediatrician and will be offered to all subjects (no invasive procedures will be carried out).