Effect of dietary tryptophan supplementation on serum biochemical indices, antioxidant capacities, cytokine levels and mitochondrial function of broilers under chronic heat stress

Abstract

Abstract This study aimed to investigate the effect of dietary tryptophan (Trp) supplementation on serum biochemical indices, antioxidant indices, cytokine levels and mitochondrial function of heat-stressed broilers. A total of 180 Arbor Acres broilers (18-d-old) were randomly allocated into 3 groups with 6 replicates and 10 broilers per replicates. Broilers in thermoneutral (TN) (23 ± 1℃) group were fed a basal diet, the other two groups were fed the basal diet or the basal diet supplemented with 0.18%Trp under heat stress (HS) (34 ± 1℃ for 8 h/d and 23 ± 1℃ for the remaining time) condition. The heat stress lasted for 21 days (days 21 to 42). The results indicted that chronic heat stress reduced serum total protein content (TP), decreased the activities of serum superoxide dismutase (SOD) and total antioxidant capacity (T-AOC), but increased the levels of serum uric acid (UA), interleukin (IL)-1β, IL-6, IL-18 (P < 0.05) compared with the TN group. However, dietary supplementation with 0.18%Trp enhanced serum TP content and glutathione peroxidase (GSH-Px), SOD, catalase (CAT) activities and T-AOC, and decreased aspartate aminotransferase (AST) activities (P < 0.05), lowered serum IL-1β, IL-6, IL-18 contents (P < 0.05). Meanwhile, chronic heat stress exposure down-regulated the mRNA expression of mitochondrial transcription factor A (TFAM), cytochrome c oxidase subunit 1 (COX1) and cytochrome c oxidase subunit 5A (COX5A) in ileum (P < 0.05) as compared with the TN group. Dietary Trp supplementation enhanced the mitochondrial membrane potential (MMP) and the mRNA expression of TFAM, COX1 in ileum mucosa (P < 0.05) and ameliorated the damage of mitochondrial structure. Collectively, dietary supplementation with Trp could improve antioxidant capacity and mitochondrial structure and regulate mitochondrial function-related genes, decreased inflammatory response in chronic heat-stressed broilers.