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 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), polycystic ovary syndrome (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.
