In a multi-centre randomised controlled trial (RCT), we are assessing whether giving very preterm (i.e., born at < 32 weeks' gestation) infants prophylactic enteral bovine lactoferrin supplementation (150 mg/kg/day) from shortly after birth until 34 weeks' post-menstrual age reduces the incidence of late-onset invasive infection (primary outcome), all-cause mortality, bronchopulmonary dysplasia, necrotising enterocolitis, retinopathy of prematurity, and the duration of antibiotic exposure, intensive care, and hospital admission. The trial is recruiting 2,200 participants from 37 neonatal care centres in the UK over 4 years. We will undertake an economic evaluation within the RCT to evaluate cost-effectiveness and provide an estimate of incremental costs for differences in the pre-specified outcomes in primary and subgroup analyses. If a statistically significant and clinically important effect on the primary outcome is detected, we will seek further funding and approval to assess the impact of enteral lactoferrin supplementation on rates of adverse neuro-developmental outcomes in the participating infants when they are 5 years old.