Effects of Immunologically Active Peptides on Growth Performance, Meat Quality, Antioxidant Capacity, and Ileum Inflammation in Broilers

Immunologically active peptides (IAP) are important bioactive peptides with potential antioxidant, anti-inflammatory, and immunomodulatory properties. However, their application in broiler production has not been systematically evaluated. This study investigated the effects of dietary IAP supplementation on growth performance, carcass traits, meat quality, selected serum biochemical indices, and ileum inflammatory cytokine expression in broilers. A total of 180 one-day-old Ross 308 male broilers were randomly assigned to 3 dietary treatments with 6 replicates per group for 42 d: a basal diet (CON), and the basal diet supplemented with 500 g/t or 1000 g/t IAP. Overall treatment tendencies were observed for final body weight (BW) and average daily gain (ADG) (p = 0.100; p = 0.096), with numerically higher values observed in broilers receiving 500 g/t IAP. Dietary supplementation with 500 g/t IAP significantly improved feed conversion ratio (p < 0.05). Across increasing dietary IAP levels, significant quadratic responses were observed for final BW, ADG, and FCR (p < 0.05), indicating nonlinear responses to increasing IAP supplementation levels. In addition, serum superoxide dismutase (SOD) activity was significantly increased in broilers receiving 500 g/t IAP compared with the control group (p < 0.05), and a significant quadratic response was observed across dietary IAP levels (p < 0.05). Furthermore, dietary IAP supplementation significantly reduced ileum interleukin-1β (IL-1β) mRNA expression in the 500 g/t group (p < 0.05), and IL-1β expression exhibited a significant quadratic response across IAP supplementation levels (p < 0.05). In conclusion, dietary supplementation with IAP, particularly at 500 g/t, improved feed efficiency, increased serum SOD activity, and reduced ileal IL-1β mRNA expression in broilers without compromising carcass characteristics or meat quality. These findings indicated that IAP has potential as a functional feed additive for further evaluation in broiler production.