Dose effects of iron on growth, antioxidant potential, intestinal morphology, and intestinal barrier in yellow-feathered broilers

This experiment was conducted to investigate the dose effects of iron on growth performance, antioxidant function, small intestinal histology, and intestinal barrier of 63-day-old yellow-feathered broilers. A total of 720 1-day-old male yellow-feathered broilers were randomly divided into 9 treatments, with 8 cages per treatment and 10 birds per cage. The Fe supplementation was 0, 20, 40, 60, 80, 160, 320, 640, and 1280 mg/kg, respectively, in the form of FeSO₄•7H₂O. The results showed that the ADG (P = 0.002) and ADFI (P < 0.001) decreased linearly with increased dietary Fe supplementation. Malondialdehyde (MDA) concentration in plasma (P = 0.001), duodenum (P < 0.001), and jejunum (P < 0.001) were increased linearly as dietary Fe increased. As dietary Fe increased, there was a linear decrease in the villus height and the villus height/crypt depth in the duodenum (P = 0.003; P = 0.001) and jejunum (P = 0.001; P < 0.001). Decreased secretory immunoglobulin A (sIgA) concentration in jejunal mucosa (P < 0.001) was observed with increased dietary Fe concentration. Lower jejunal sIgA concentrations were observed in birds consuming more than 160 mg/kg of Fe (P < 0.001). A quadratic response was found for jejunal diamine oxidase (DAO) activity (P = 0.011) as dietary Fe supplementation was increased. The highest response of DAO in jejunal mucosa was observed for broilers supplemented with 160 mg/kg of Fe. Furthermore, the mRNA expressions of ZO-1 (P < 0.001), occludin (P = 0.004), and claudin-1 (P = 0.007) in jejunal mucosa decreased linearly with increased dietary Fe concentration. Data from the study suggests that there is no need to supplement additional Fe to a corn-soybean-based diet for yellow-feathered broilers based on growth performance, antioxidant potential, small intestinal histology, and intestinal barrier. Chronic iron exposure (≥ 160 mg/kg) can damage the intestinal barrier function, and further increase of Fe supplementation can lead to oxidative stress and even cause growth inhibition for yellow-feathered broilers.