Background: The influences of nutrition on the infant's developing gastrointestinal (GI) microbiome, intestinal tract, and brain is unclear. Human milk (HM) is associated with beneficial immune and cognitive development compared with infant formula (IF). This study used a neonatal piglet model to determine the effects of infant feeding exposures (HM vs IF) on the GI microbiome, intestinal inflammation, and brain oligodendrocyte maturation. Methods: Six pairs of piglets received HM or IF for 28 days. Fecal samples were collected weekly and GI regions (jejunum, ileum, and colon) and brains were harvested at necropsy. Fecal microbiome composition was determined by 16S ribosomal RNA (16S rRNA) sequencing. Intestinal inflammation was assessed via quantification of intestinal interleukin (IL)‐1β, IL‐8, IL‐10, tumor necrosis factor (TNF)‐α, and fecal calprotectin. Neurodevelopment was evaluated by quantifying mature and immature oligodendrocytes in gray and white matter. Results: Bacterial community composition differed between feeding groups ( P < 0.002) and over time ( P = 0.001). Various highly abundant genera were associated with changes over time ( P < 0.05) and only Escherichia‐Shigella was associated with feeding group by time interactions ( P < 0.05). No differences were found in intestinal inflammatory markers between feeding types, but mature oligodendrocytes in white matter were higher in HM‐fed piglets ( P = 0.004). Various intestinal inflammatory markers and relatively highly abundant genera were significantly associated. Conclusion: Piglet fecal bacterial compositions differed by feeding group and over time, with several relatively highly abundant genera associated with intestinal inflammatory markers. Additionally, HM may support proper white matter development. Future research should investigate mechanisms underlying these relationships.

Human milk (HM) feedings are associated with reduced risks of neurodevelopmental and neurocognitive delays and systemic inflammatory diseases in infants born prematurely and/or at a low birth weight. Utilizing a neonatal piglet model, HM feedings were compared to bovine milk-derived infant formula (IF)-feedings with the aim of understanding the underlying mechanisms involved in reducing these risks. Six male piglets at postnatal-day (PD)2 were randomized into two feeding groups: HM-fed (n = 3) or IF-fed (n = 3) for 28 days. At 3- and 4-weeks-old, piglet memory and learning performance were assessed using novel object recognition (NOR). At PD30 piglets were euthanized, and whole brains were excised, weighed, and preserved for further analyses, and brain microglial morphology, and systemic inflammatory cytokines were quantified. During NOR, HM-fed piglets had significantly more non-novel revisits at both 3- and 4-weeks-old compared to IF-fed piglets. Microglia of HM-fed piglets had longer processes, more branch points, more endpoints, and a larger territorial volume compared to IF-fed piglets at PD30. In a neonatal piglet model, HM-feedings may improve cognition and reduce brain inflammatory response compared to IF-feedings.