IDENTIFYING THE CRITICAL REGULATORS OF THE METABOLIC SWITCH FROM EMBRYONIC LIPID UTILIZATION TO POST-HATCH CARBOHYDRATE USE AND LIPID SYNTHESIS IS OF SIGNIFICANCE TO IMPROVE POULTRY PRODUCTION. THIS PROPOSAL WILL DETERMINE THE ROLE OF SPECIFIC MACRONUTRIENT GROUPS (CARBOHYDRATE, PROTEIN, LIPID) IN INITIATING THIS METABOLIC SWITCH POST-HATCH. WE HYPOTHESIZE THAT THE COORDINATED INDUCTION OF BIOCHEMICAL FLUX THROUGH MITOCHONDRIAL NUTRIENT SHUTTLES AND TRICARBOXYLIC ACID (TCA) CYCLE IS A PREREQUISITE FOR THE EFFICIENT METABOLIC SWITCH. REMODELING OF MITOCHONDRIAL FUNCTION WILL BE EVALUATED IN LIVER, SMALL INTESTINE (DUODENUM PLUS JEJUNUM) WHICH A) TOGETHER ACCOUNTS FOR OVER 20% OF WHOLE-BODY OXYGEN CONSUMPTION AND B) HAS CONTRASTING BIOCHEMICAL FUNCTIONS (GLUCONEOGENESIS-LIPOGENESIS FOR LIVER VS. NUTRIENT ABSORPTION/ OXIDATION FOR SMALL INTESTINE). OBJECTIVE 1 WILL UTILIZE STABLE-ISOTOPE/ MASS-SPECTROMETRY BASED METABOLIC PROFILING TO A) DETERMINE CHANGES IN ACTIVITY OF MITOCHONDRIAL NUTRIENT SHUTTLES AND TCA CYCLE IN RESPONSE TO SPECIFIC MACRONUTRIENTS AND B) DETERMINE WHETHER LIVER VS. SMALL INTESTINAL MITOCHONDRIAL ENERGETICS RESPOND DIFFERENTLY TO MACRONUTRIENTS DURING THE METABOLIC SWITCH POST-HATCH. OBJECTIVE 2 WILL UTILIZE RNA-SEQUENCING TO DETERMINE THE IMPACT OF MACRONUTRIENTS ON GENE NETWORKS IN THE LIVER AND SMALL INTESTINE. PROMINENT CORRELATIONS BETWEEN BIOCHEMICAL FLUX (OBJECTIVE 1) AND GENE NETWORKS (OBJECTIVE 2), SPECIFICALLY IMPACTING NUTRIENT METABOLISM AND MITOCHONDRIAL FUNCTION WILL BE IDENTIFIED. THESE UNIQUE BIOCHEMICAL AND MOLECULAR NETWORKS WILL PRESENT NEW TARGETS TO REDUCE EARLY MORBIDITY AND MORTALITY AND TO OPTIMIZE GROWTH AND PRODUCTIVITY IN CHICKENS, THROUGH IN OVO OR EARLY POST-HATCH FEEDING OF CUSTOMIZED NUTRITIONAL FORMULATIONS.