OBJECTIVES: Exclusive feeding with bovine colostrum (BC) protects preterm pigs against necrotizing enterocolitis (NEC) and BC has recently been tested as a supplement to a mother's own milk or formula (FOR) for very preterm infants. Using preterm pigs as a model for infants, we investigated if BC has gut- and NEC-protective effects at different proportions of the daily enteral intake given as BC. METHODS: Sixty-eight caesarean-delivered preterm piglets (90% gestation) were allocated into four groups with increasing proportions of eight daily bolus feedings as BC: BC00 (only FOR feeding), BC25 (25% BC), BC50 (50% BC), or BC75 (75% BC). On day 5, the gut was collected for biochemical analyses. RESULTS: Body growth was increased in BC50 and BC75 piglets (2-fold, P < 0.05 vs BC00). The incidence of mild NEC-like lesions was similar among groups (67-86%), but BC75 reduced severe NEC-like lesions (27% vs 79% in BC00, P < 0.05). BC50 and BC75 improved hexose absorption and mucosal structure and reduced gut permeability (P < 0.05 vs BC00), while enzyme activities (lactase, aminopeptidase N and A, dipeptidyl peptidase IV) were improved in all pigs fed BC (P < 0.05). Across the measured variables, beneficial effects were most clear for the BC75 group, including reductions in colon tissue cytokine levels (interleukin 8, interleukin 1β, tumor necrosis factor α) and expression of immune- and apoptosis-related genes (LBP, TLR4, TLR2, IL8, STAT3, IL17, C3, all P < 0.05, relative to BC00). CONCLUSION: A proportion of 50-75% of daily enteral intake as BC is required to improve the intestinal structure, function, immunology, and NEC resistance in preterm piglets also fed formula. Further studies are required to show if and how supplementary BC may support gut development in preterm infants during the immediate postnatal period. It is challenging to translate results on optimal feeding regimens between species, and preterm infants would not receive a majority of their daily enteral intake as BC.