Background: Human milk for very preterm infants need fortification for optimal growth and development but the optimal fortification product remains to be identified. Aims: To investigate feasibility, safety and preliminary efficacy on growth and blood biochemistry when using intact bovine colostrum (BC) as a fortifier to human milk in very preterm infants. Methods: In an open-label, multicenter, randomized controlled pilot trial (infants 26–31 weeks' gestation), mother's own milk or donor human milk was fortified with powdered BC (n = 115) or a conventional fortifier (CF, bovine-milk-based, n = 117) until 35 weeks’ postmenstrual age. Fortifiers and additional micronutrients were added to human milk according to local guidelines to achieve optimal growth (additional protein up to +1.4 g protein/100 mL human milk). Anthropometry was recorded weekly. Clinical morbidities including necrotizing enterocolitis (NEC) and late-onset sepsis (LOS) were recorded. Clinical biochemistry included plasma amino acid (AA) levels to assess protein metabolic responses to the new fortifier. Results: A total of 232 infants, gestational age (GA) 28.5 ± 1.4 (weeks + days), fulfilled inclusion criteria. Birthweight, GA and delta Z scores from birth to end of intervention on weight, length or head circumference did not differ between groups, nor between the subgroups of small for gestational age infants. Likewise, incidence of NEC (BC: 3/115 vs. CF: 5/117, p = 0.72, unadjusted values), LOS (BC: 23/113 vs. CF: 14/116, p = 0.08) and other morbidities did not differ. BC infants received more protein than CF infants (+10%, p < 0.05) and showed several elevated AA levels (+10–40%, p < 0.05). Conclusion: Infants fortified with BC showed similar growth but received more protein and showed a moderate increase in plasma AA-levels, compared with CF. Adjustments in protein composition and micronutrients in BC-based fortifiers may be required to fully suit the needs for very preterm infants.