Universally, extremely preterm infants experience a delayed and slowly progressive advancement in enteral feedings often after a period of parenteral nutrition Unfortunately, this common nutritional strategy in the neonatal ICU fails to maintain critical blood levels of long chain polyunsaturated fatty acids (LCPUFAs) that the premature infant would have been exposed to in utero had they not been born early. The importance of selective LCPUFA excesses and deficiencies is highlighted by their clinical associations and causation in preterm animal models for chronic lung disease, sepsis, retinopathy of prematurity, and necrotizing enterocolitis (NEC). Our overall hypothesis is that early priming driven by parenteral nutrition and subsequent abnormal LCPUFA profiles lead to maladaptive systemic and intestinal host responses in the preterm infant increasing their risk of disease. Our group has shown that the currently administered parenteral lipid emulsion (Intralipid) results in a 2-3 fold reduction in blood levels of Docosahexaenoic Acid (DHA) and Arachidonic Acid (AA) concomitant with a 2.5 fold increase in Linoleic Acid (LA) within the first postnatal week. These profound changes in blood LCPUFA profiles were associated with a later increased risk of chronic lung disease and nosocomial sepsis. NEC, a life-threatening disease characterized by inflammation and necrosis largely confined to the ileum and occurring almost exclusively in preterm infants, is an ideal model to study the effect of early priming by altered LCPUFA levels since it almost exclusively occurs within a short time frame after initiation of enteral feedings often following exposure to parenteral nutrition when fatty acid alterations have already been established. This application will build upon our prior studies and test our central hypothesis that early exposure to altered profiles of LCPUFAs primes the premature infant's host responses and subsequent intestinal adaptive responses to the introduction of enteral feedings increasing the risk of NEC. Our approach utilizing a world renown collaborative team that brings together leaders in omics strategies, fatty acid metabolism, neonatal outcomes, and nutritional impact studies in preterm piglets at Baylor USDA, will take advantage of ongoing complimentary animal models of NEC to evaluate the priming effect of altered fatty acids induced by parenteral provision of lipid emulsions (preterm piglet model, Aim 1) and to directly evaluate the developmental intestinal adaptations of varying enteral fatty acids (murine pup model, Aim 2). Together, preterm host response pathways that are modulated by nutritional provision of critical fatty acids (parenteral and enteral) will be identified using a transcriptomis and metabolomics strategy complimented by western blot, Luminex and histologic analyses. Taken together, these animal models will allow us to rigorously test our hypothesis and define the molecular signatures of the host's adaptive responses in models of prematurity induced by nutritional alterations of critical PUFAs.