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Artificial rearing and formula feeding is coming more into the focus due to increasing litter sizes and limited nursing capacity of sows. The formula composition is important to effectively support the development of the gut and prevent intestinal dysfunction in neonatal piglets. In this study, newborn piglets (n = 8 per group) were fed a bovine milk–based formula (FO), containing skimmed milk and whey as the sole protein and carbohydrate sources, or were suckled by the sow (sow milk [SM]). After 2 wk, tissue from the jejunum was analyzed for structural (i.e., morphometry) and functional (i.e., disaccharidase activity, glucose transport, permeability toward macromolecules, and immune cell presence) changes and concomitant expression of related genes. Formula-fed piglets had more liquid feces (P < 0.05) over the entire experimental period. Although FO contained twice as much lactose (46% on a DM basis) as SM (21%) and no maltose or starch, the lactase activity was lower (P < 0.05) and glucose transport capacity was higher (P < 0.05) in FO-fed pigs. The relative proportion of intraepithelial natural killer cells and proinflammatory cytokine gene expression (IL-8, TNF-a, and IFN-y) was higher in FO-fed pigs (P < 0.05). Piglets fed FO had deeper crypts, larger villus area, and higher expression of caspase 3 and proliferating cell nuclear antigen (P < 0.05). Epithelial permeability toward fluorescein isothiocyanate–dextran was higher and expression of claudin-4 was lower in FO-fed piglets (P < 0.05). The data suggest an early response to bovine milk–based compounds in the FO accompanied with early onset of functional maturation and impaired barrier function. Whether lactose, absence of species-specific protective factors, or antigenicity of foreign proteins lead to to the observed intestinal reactions requires further clarification.