Monochromatic Blue Light Enhances Antioxidant Status and Remodels the Gut Microbiome in Association with Increased Plasma Melatonin in Broiler Chickens.

The intestinal microbiome of broiler chickens has potential to regulate host health and growth performance. Although previous studies have revealed that the intestinal microbiota composition is affected by different factors including monochromatic light, the underlying mechanisms remain poorly understood, particularly regarding the causal role of light-sensitive hormones such as melatonin. To address this gap, a 2 × 4 factorial design was adopted in the present study, with two surgical treatments (sham-operation or pinealectomy) and four light conditions (white, blue, green, and red light), to investigate whether blue light modulates gut microbiota and antioxidant status through melatonin-dependent pathways. Broilers were reared under different monochromatic light conditions. On day 3 post-hatching, we ablated circulating melatonin production by conducting a pinealectomy or control sham-operation model. Accordingly, the broilers were assigned to eight groups: white light + sham-operation (WL), white light + pinealectomy (WP), blue light + sham-operation (BL), blue light + pinealectomy (BP), green light + sham-operation (GL), green light + pinealectomy (GP), red light + sham-operation (RL), and red light + pinealectomy (RP). On day 35, blue light was found to most effectively elevate plasma melatonin, which activated the Mel 1a/Nrf2/NQO1 pathway to reduce oxidative stress and remodel the jejunal microbiota. Metagenomic analysis identified Akkermansia muciniphila, Bifidobacterium longum and Ligilactobacillus aviarius as key bacteria enriched in blue light. Consequently, classes of microbiota-derived metabolites like stearidonic acid and indole propionic acid triggered the variation of tryptophan, bile acid and lipid metabolism, which contributed to broiler growth promotion. Moreover, pinealectomy accompanied by plasma melatonin deprivation significantly nullified the blue-light-induced effects. These insights confirm blue light is more effective in microbiota modulation by inducing melatonin secretion and providing a new strategy for light management in the broiler industry.