Health effects of astaxanthin in the intestinal tract of yellow-feathered broilers

Astaxanthin (AST), a keto carotenoid, is widely recognized for its antioxidant, anti-inflammatory, and apoptosis-regulating properties, but its effects on intestinal health have not been elucidated. Therefore, this experiment aimed to investigate the effects of astaxanthin on intestinal morphology, barrier function, mucosal immunity, and cecal flora in yellow-feathered broilers, and to explore the potential mechanisms. A total of 288 male yellow-feathered broilers (1-day-old) were randomly allocated to four groups with six replicates of 12 birds each. The control group (CON) was fed a basal diet, the test groups were fed a basal diet added with 20 mg/kg, 40 mg/kg, and 80mg/kg of astaxanthin (AST20, AST40, and AST80), respectively. The results showed that compared with the CON group, the villus height and the villus-to-crypt ratio of broiler jejunum in the astaxanthin-added group increased, while the crypt depth decreased (P < 0.05). In addition, IL-1β content and gene expression in broiler jejunal mucosa decreased, IL-6 gene expression decreased, and IL-4 content and gene expression increased (P < 0.05). The tight junction protein ZO-1 expression level in the jejunum mucosa of broilers was up-regulated, and the content of serum D-lactic acid was decreased (P < 0.05). Besides, the α-diversity and β-diversity analyses showed that astaxanthin regulated both the diversity and the structure of the intestinal flora of broilers. After multiple comparative analyses, the relative abundance of norank_f__Eubacterium_coprostanoligenes_group, Lachnospiraceae NC2004_group, and unclassified_p_Firmicutes increased in the AST20 group compared to the CON group, while that of Ruminococcus_torques_group in the AST80 group decreased (P < 0.05). Therefore, AST can regulate the immune function of broiler intestinal mucosa, improve intestinal morphology and structure, and then influence intestinal permeability. It also has a considerable regulatory effect on the diversity and structure of broiler intestinal flora and plays a multifaceted role in maintaining broiler intestinal health.