Monochromatic light affects intestinal barrier function of chick via an anti-oxidation pathway involving melatonin and its receptor Mel1b

Extensive evidence indicated that monochromatic lights could significantly affect broiler growth performance and intestinal function. However, the exact underlying mechanisms remain unknown. In this study, we focused on the photosensitive hormone melatonin due to its high photosensitivity in broilers to investigate the changes in broiler intestinal function under different monochromatic lights. Broilers were randomly assigned to four light colors: white light (WL), blue light (BL), green light (GL), red light (RL). At post-hatching day 3, half of broilers from each light color were pinealectomized. All birds were reared until post-hatching day 21 and their blood and jejunum were collected. The results revealed that monochromatic blue and green light significantly elevated plasma melatonin concentration and improved jejunal function by significantly increasing broiler weight, villus height, villus height/crypt depth ratio (V/C) and decreasing crypt depth compared to red light. Additionally, blue and green light up-regulated Claudin1, Occludin, ZO-1, Pept1, SglT1, Si, Cat1 gene expression and down-regulated Cat2 expression compared to red light. Moreover, blue and green light elevated goblet cell and IgA-positive cell numbers and boosted relative mRNA expression of Muc2, SOD, CAT and GSH-Px when compared with red light. Notably, pinealectomy eliminated differences among four light groups and impaired broiler jejunal function more than their sham-operated counterparts along with an ablation in plasma melatonin level. Further investigation demonstrated that melatonin significantly improved jejunal function by suppressing intestinal cell apoptosis instead of promoting cell proliferation. In vitro experiments indicated that melatonin primarily exerts its anti-apoptotic effects via the Mel1b receptor. In summary, our study revealed that melatonin mediates the effects of monochromatic blue and green light on reducing broiler jejunal oxidative stress level and cell apoptosis via Mel1b receptor, which may finally improved intestinal function. Our research provides a theoretical support for the effect of monochromatic light on melatonin production and the subsequent gut function improvement. It also suggests that monochromatic light could be applied as an antibiotic-free strategy in sustainable animal agriculture to improve gut health and broiler production.