This study investigated the individual and synergistic effects of exogenous emulsifiers and lipase supplementation on growth performance, nutrient apparent digestibility, lipid metabolism, and gene expression in broilers receiving reduced-energy diets. All diets formulated using identical ingredient ratios except for energy-contributing components, which were adjusted through modification in soybean oil content to achieve target energy levels while maintaining amino acid profiles.

Three hundred one-day-old male Ross 308 broiler chicks were randomly allocated to five treatment groups. The experiment consisted of 30 pens, with 10 birds per pen. Each treatment group included 6 replicate pens (n = 60 birds per treatment). positive control (PC) fed standard energy diets; negative control (NC) fed diets with 80 kcal/kg energy reduction; NC + emulsifier (250 g/ton Emulsifier equivalent to (20 g lysophospholipids/ton of feed); NC + lipase (100 g/ton equivalent 1 million lipase unit/ton of feed equivalent); and NC + combined emulsifier and lipase supplementation.

Results demonstrated that energy reduction significantly impaired body weight gain and feed conversion ratio compared to PC birds. However, combined emulsifier and lipase supplementation restored growth performance parameters compared with NC, achieving superior body weight gain (2,222 g vs. 2,053 g in NC group) and improved feed conversion efficiency (1.344 vs. 1.491 in NC group).

Crude protein retention increased significantly in emulsifier-supplemented groups (81.4–81.8% vs. 76.3% in NC), while ether extract retention improved across all supplemented treatments. Carcass characteristics remained unaffected, though abdominal fat deposition decreased significantly in all reduced-energy groups compared to PC birds.

Serum biochemical analysis revealed beneficial effects on lipid metabolism, with total cholesterol and triglyceride concentrations decreasing in supplemented groups. Antioxidant status improved, evidenced by elevated glutathione peroxidase activity and reduced malondialdehyde concentration in liver tissue of treated birds.

Histological examination revealed that energy reduction caused intestinal villus atrophy and enteritis in NC birds, while emulsifier and lipase restored normal villus architecture. Gene expression analysis showed significant downregulation of insulin-like growth factor (IGF-1) mRNA in NC birds, which was restored to PC levels following combined supplementation. These findings indicate that lysophospholipid emulsifiers and exogenous lipase can effectively compensate reduced dietary energy density in broiler diets.