An Examination of Infants' Microbiome, Nutrition, and Development Study.

Inclusion Criteria: * Women, age 21 to 45 years who have delivered a healthy single infant by vaginal delivery and their infants, age 4 to 7.5 months; * Infants who are developmentally ready for solids; * Generally healthy women and infants; * Mothers who plan to exclusively (without solids or infant formula) breastfeed (at the breast or feed breast milk by bottle) their infants for at least 5 months of age and plan to continue to breastfeed with solids and/or infant formula until 12 months of age; * Mothers who are willing to either use their own breast pump, or hand-express, or use a manual pump provided by the study to collect milk samples; * Mothers who are willing to refrain from feeding their infants infant formula, non-study solid foods; probiotic or iron supplements (confounding variables of the intestinal microbiome) before the end of the feeding intervention period; * Term infants born \>37 weeks gestation; * Mother-infant pairs who live within a 20-mile radius from University of California, Davis campus in Davis, California (includes Woodland, Vacaville, Dixon and surrounding areas) or within a 20-mile radius of the University of California, Davis Medical Center (UCDMC) (2221 Stockton Blvd, Sacramento, CA 95817). Exclusion Criteria: * Infants with any GI tract abnormalities; * Infants born by cesarean section; * Family history of immunodeficiency syndrome(s); * Multiple infants born to one mother at the same time (no twins, triplets, etc.); * Infants born with m…