 Stool samples will be collected twice weekly for the first six weeks of life then once weekly at weeks 24, 36, 52 and 78. Stool samples will be analyzed to determine the relative abundance of B. infantis over time, and the overall diversity of the gut microbiota with and without B. infantis supplementation. Stool will also be analyzed for milk oligosaccharides to verify consumption of breast milk and to correlate proportion of human milk oligosaccharides and free sugar monomers seen in the infant stool at various levels of B. infantis colonization. 