Effects of dietary Chlorella vulgaris and cinnamon oil on growth performance, gut morphology, digestive enzymes, and intestinal gene expression in broilers

Antibiotic-free broiler production has increased interest in natural feed additives such as dried <i>Chlorella vulgaris</i> (DCV) and cinnamon oil (CO). This study evaluated DCV, CO, and their combination (DCV&CO) on growth, intestinal function, and immune responses in broilers at 42 days of age. One hundred twenty one-day-old male broilers were allocated to four dietary treatments (six replicates × five birds): CTRL (basal diet), DCV (1 g/kg diet), CO (0.1 g/kg diet), and DCV&CO (1 g/kg DCV + 0.1 g/kg CO). Growth performance, plasma metabolites, jejunal histomorphometry, digestive enzyme activities, and jejunal mRNA transcripts related to nutrient transport, tight junction function, and cytokine activity were assessed. Broilers fed DCV showed higher body weight gain and better feed conversion ratio (<i>P</i> < < 0.01) without affecting feed intake. CO elevated plasma triglycerides (<i>P</i> < 0.05). Jejunal villus height, villus-to-crypt ratio, and villus area were greater in DCV and DCV&CO (<i>P</i> < 0.05). Lipase activity increased in all supplemented groups; amylase was higher with DCV; protease was higher only with DCV&CO (<i>P</i> < 0.05). Supplemented diets upregulated mRNA expression of nutrient transporters (<i>EAAT3, GLUT2, SGLT1, PEPT1, CAT-1</i>) and tight junction markers (<i>MUC2, TJP2, OCLN, CLDN1, TJP1</i>). Cytokines were modulated: <i>IL-1β</i> increased in DCV, <i>IL-8</i> in DCV&CO, and <i>TNF-α</i> decreased in all supplemented groups (<i>P</i> < 0.05). DCV and CO, alone or combined, improved growth, intestinal morphology, digestive enzyme activities, and gut barrier function while modulating pro-inflammatory cytokines, supporting their use as natural alternatives to antibiotic growth promoters.