Infants' Microbiome, Nutrition, and Development

Eligibility Details: 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 UC Davis campus in Davis, CA (includes Woodland, Vacaville, Dixon and surrounding areas) or within a 20-mile 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 medical complications such as: respiratory distress syndrome, birth defects, and infection; - Mothers diagnosed with any metabolic or endocrine, liver, kidney disease, any autoimmune disease, cirrhosis, hepatitis C, HIV, AIDs, cancer, obesity (pre-pregnancy BMI >34.9), PCOS, celiac disease, Crohn's disease, heart disease, hyper- or hypothyroidism, hyper- or hypotension (including pre-eclampsia), type 1 or type 2 diabetes. - Mothers who smoked cigarettes less than one month before becoming pregnant, during pregnancy, and currently or mothers who plan to initiate smoking during the study duration; - Infants who have taken antibiotics within the past 4 weeks; - Infants who have taken iron supplements within the past 4 weeks; - Infants who have consumed infant formula in the past 4 weeks; - Infants who have consumed infant formula more than 10 days between birth and 4 weeks prior to screening; - Infants who have consumed any solids; - Mothers who plan to feed infants solids before 5 months of age; - Mothers who plan to administer any probiotics to infants throughout the feeding intervention period (first 18 days of the study); - Infants who have consumed probiotics containing Bifidobacterium within the past 4 weeks or other probiotics within the past 7 days; - Mothers who live in more than one location (should only live in one house to ensure samples are correctly collected and stored); - Infants who have hypotonia, - Infants who have been diagnosed with any medical or nutritional condition that would require iron supplementation. - Infants who on average pass less than one stool per week.