Responses of growth performance, antioxidant function, small intestinal morphology and mRNA expression of jejunal tight junction protein to dietary iron in yellow-feathered broilers

This study aimed to investigate the dose-effect of iron on growth performance, antioxidant function, intestinal morphology, and mRNA expression of jejunal tight junction protein in 1- to 21-d-old yellow-feathered broilers. A total of 720 1-d-old yellow-feathered male broilers were allocated to 9 treatments with 8 replicate cages of 10 birds per cage. The dietary treatments were consisted of a basal diet (contained 79.6 mg Fe kg(-1)) supplemented with 0, 20, 40, 60, 80, 160, 320, 640, and 1,280 mg Fe kg(-1) in the form of FeSO4 center dot 7H(2)O. Compared with the birds in the control group, birds supplemented with 20 mg Fe kg(-1) had higher average daily gain (ADG) (P<0.0001). Adding 640 and 1,280 mg Fe kg(-1) significantly decreased ADG (P<0.0001) and average daily feed intake (ADFI) (P<0.0001) compared with supplementation of 20 mg Fe kg(-1). Malondialdehyde (MDA) concentration in plasma and duodenum increased linearly (P<0.0001), but MDA concentration in liver and jejunum increased linearly (P<0.05) or quadratically (P<0.05) with increased dietary Fe concentration. The villus height (VH) in duodenum and jejunum, and the ratio of villus height to crypt depth (V/C) in duodenum decreased linearly (P<0.05) as dietary Fe increased. As dietary Fe increased, the jejunal relative mRNA abundance of claudin-1 decreased linearly (P=0.001), but the jejunal relative mRNA abundance of zona occludens-1 (ZO-1) and occludin decreased linearly (P<0.05) or quadratically (P<0.05). Compared with the supplementation of 20 mg Fe kg(-1), the supplementation of 640 mg Fe kg(-1) or higher increased (P<0.05) MDA concentrations in plasma, duodenum, and jejunum, decreased VH in the duodenum and jejunum, and the addition of 1,280 mg Fe kg(-1) reduced (P<0.05) the jejunal tight junction protein (claudin-1, ZO-1, occludin) mRNA abundance. In summary, 640 mg of supplemental Fe kg(-1) or greater was associated with decreased growth performance, increased oxidative stress, disrupted intestinal morphology, and reduced mRNA expression of jejunal tight junction protein.