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 FeSO4·7H2O.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.