OBJECTIVE: To examine associations between enteral feed type with neurodevelopmental and neonatal outcomes among infants born preterm. STUDY DESIGN: This was a retrospective study of enteral feeds in the first 28 postnatal days in infants born <
29 weeks' gestation from 2015 through 2020 in neonatal units of the Canadian Neonatal Network and Canadian Neonatal Follow-Up Network. Feeds were examined as a compositional variable comprised of the proportion of days fed mother's milk, donor milk, mixed feeds, and nil per os (NPO), the proportions of which sum to 1. Associations between enteral feed type with neurodevelopmental outcomes at 18 to 24 months corrected age and neonatal morbidities were examined. RESULTS: Our cohort included 2104 infants with a mean (SD) gestational age of 26.2 (1.5) weeks (52.9% male). Compositional data analysis revealed a one-day reallocation from mother's milk to donor milk was associated with greater odds of cognitive (aOR: 1.028, 95%CI: 1.001, 1.056) and language impairment (aOR: 1.024, 95%CI: 1.002, 1.047). Replacing one day of mixed feeds, donor milk or NPO with mother's milk was associated with improved cognitive, language and motor development. A one-day reallocation of NPO to either mother's milk, mixed feeds or donor milk decreased odds of significant neurodevelopmental impairment, cerebral palsy and/or necrotizing enterocolitis. CONCLUSIONS: Donor milk in place of mother's milk was associated with poorer cognitive and language development. Providing any human milk reduced neurodevelopmental impairment and necrotizing enterocolitis with reallocations involving mother's milk yielding the most benefit. Promoting early enteral nutrition with mother's milk should be a priority in the care of infants born preterm.