Energy restriction optimizes energy partitioning and remodels intestinal energy metabolism in layer pullets

This study aimed to investigate the effects of different energy-restricted program on energy metabolism in layer pullets. A total of 168 birds were randomly divided into 3 groups: regular energy (RE), energy level restriction (ER, 0.55 MJ/kg lower than RE) and feed restriction (FR, about 88 % of ad libitum intake), with 7 replicates per group and 8 birds per replicate. Indirect calorimetry and targeted metabolomics were employed to assess energy partitioning and intestinal metabolic profiles in pullets across different groups. Results showed that feed restriction significantly decreased feed conversion ratio (FCR), apparent metabolizable energy (AME) intake, retained energy and retained energy as fat compared to RE group (P < 0.05). Moreover, feed restriction up-regulated ileal gene expression of glucose transporter 2 (GLUT2), phosphofructokinase (PFK) and Na⁺/K⁺-ATPase β1 subunit (ATP1B1) in pullets (P < 0.05). Compared to RE group, energy level restriction improved retained energy as protein in pullets (P < 0.05). Additionally, pullets in ER group exhibited significantly (P < 0.05) increased adenosine monophosphate (AMP)/adenosine triphosphate (ATP) ratio and reduced adenylate energy charge (AEC) content. In terms of metabolic profiling, energy restriction down-regulated 7 metabolites in ileum, including glycolytic intermediates, such as phosphoenolpyruvate (PEP), fructose-1,6-biophosphate (F-1,6-BP) and 2-phosphoglycerate (2-PGA), while feed restriction decreased two metabolites and improved flavin-mononucleotide content in ileal mucosa. Hence, both feed and energy level restriction optimized energy deposition without compromising intestinal morphology and growth performance. Energy level restriction decreased energy status in ileal mucosa, as evidenced by reduced AEC content primarily resulting from suppressed glycolytic flux.