In the pig, the gastrointestinal tract grows rapidly after birth and undergoes a short postnatal maturation. The objective of the present work was to assess the metabolic characteristics of the small intestinal mucosa during this period by investigating glucose, galactose, and glutamine metabolism in pig isolated enterocytes. Piglets were used immediately after birth or at various stages during suckling or postweaning. Fed animals were taken in a postabsorptive state. The jejunoileum was excised and perfused with an EDTA (5 mM)-containing buffer. The epithelial cell layer was further dissociated in the presence of hyaluronidase (0.01%). The resulting cell suspension (95% absorbing enterocytes; viability greater than 90%) was incubated with 14C-labeled substrates to measure 14CO2 production in parallel with substrate disappearance. The capacity to utilize glutamine was high and remained steady during the suckling period. Glucose utilization capacity was limited at birth and increased more than 3-fold during the first week of suckling. Such an increase was not observed in piglets kept unsuckled since birth. Galactose utilization capacity remained steady during the first week but afterward gradually disappeared. Lactate and pyruvate production through glycolysis was the major pathway accounting for glucose or galactose disappearance. A capacity for a net glucose production from galactose was evidenced during the first week of suckling. Thus, isolated newborn pig enterocytes exhibit specific and transient metabolic characteristics during the first postnatal week.