Study On Characteristics And Mechanisms Of Absorptions Of Iron From Different Iron Sources In The Small Intestine Of Broilers

Two experiments were conducted to investigate the characteristics and mechanisms of absorptions of iron(Fe) from organic Fe sources with different chelation strength and inorganic ferrous sulfate(Fe SO4) in the small intestine of broilers by the method of in situ ligated and perfused intestinal loops and practical feeding.Two trials in the first experiment were conducted to investigate the characteristics of absorption of Fe from different Fe sources in the small intestine of broilers by the method of in situ ligated and perfused intestinal loops. In trial 1, 8 treatments were arranged in a single factor completely randomized design. And the in situ ligated intestinal loops from the chicks were perfused with solutions containing 0 mmol Fe/L, or 0.45 mmol Fe/L from Fe SO4(Fe SO4·7H2O), Fe-Gly chelate, one of three Fe-amino acid or protein complexes with weak(Qf =1.37), moderate(Qf =43.6)or extremely strong(Qf =8.59×103)complex strength(Fe-Met W, Fe-Pro M, or Fe-Pro ES), or the mixtures of Fe SO4 with either Gly or Met(Fe + Gly or Fe + Met), respectively, up to 30 min. In trial 2, 25 treatments were arranged in a 4×6+1 completely randomized design. The in situ ligated duodenal loops from the Fe-deficient chicks were perfused with solutions containing 6.25μg/ml(0.11 m M)、12.5μg/ml(0.22 m M)、25μg/ml(0.45 m M)、50μg/ml(0.9 m M)、100μg/ml(1.79 m M) and 200μg/ml(3.58 m M) Fe from Fe SO4, Fe-Met W, Fe-Pro M, and Fe-Pro ES, respectively, up to 30 min. Meanwhile, the treatment without Fe was set as the control one. The results from the trial 1 showed that the absorptions of Fe from both inorganic and organic Fe sources in the ligated duodenum were about 1.35–2.8 times higher(P < 0.05) than those in the ligated jejunum or ileum, and no differenecs were observed in the Fe absorption velocity among all the treatments. The results from the trial 2 showed that:(1) The absorption of Fe as Fe-Pro M or Fe-Pro ES was higher(P < 0.05) than that of Fe as inorganic Fe or Fe-Met W at Fe concentration of 3.58mmol/L.(2) The absorption kinetics of Fe from organic and inorganic Fe sources in the ligated duodenal loops followed a saturable carrier-mediated process as determined by regression analysis of concentration-dependent absorption rates.(3) The maximum absorption velocity(Jmax) and Michaelis–Menten constant(Km) values in the ligated duodenal loops were higher(P < 0.05) for Fe-Pro M and Fe-Pro ES than for Fe SO4 and Fe-Met W. The results from the first experiment indicate that the duodenum was the main site of Fe absorption in the intestines of broilers, and Fe absorption of different Fe sources in the duodenum followed a saturable carrier-mediated process; Fe-Pro M or Fe-Pro ES showed higher Fe absorptions than inorganic Fe or Fe-Met W at a higher concentration of added Fe; And the simple mixture of Fe SO4 with amino acids did not increase Fe absorption.The second experiment was conducted to investigate the effect of Fe source on Fe content in the plasma from portal vein blood and gene expression Fe transporters in the small intestine of broilers by the method of practical feeding, so as to study the the differences and mechanisms of Fe absorption of different Fe sources. A total of 600 1-d-old Arbor Acres commercial male broilers were fed a dextrose-casein purified diet containing 3.26 mg/kg Fe for one week, during which Fe stores in the body were depleted. At the age of 7 d, 480 birds were selected according to the average weight and allotted randomly to 1 of 8 replicate cages(12 chicks per replicate cage) for each of 5 treatments. Birds were fed a corn-soybean meal basal diet(the control, containing 69.86 mg/kg Fe) or the basal diet supplemented with 60 mg/kg Fe as Fe SO4·7H2O, Fe-Met W, Fe-Pro M, and Fe-Pro ES, respectively, for 14 d. The results showed that:(1) No differences were found in the Fe contents in plasma from the hepatic portal vein on d 7 post-feeding among different Fe treatments(P =0.9985). on d 14 post-feeding, Fe contents in plasma from the hepatic portal vein were higher(P =0.0001) for the birds fed diets supplemented with Fe than for the birds fed the control diet. In addition, Fe contents in plasma from the hepatic portal vein were higher(P<0.01) for the birds fed diet supplemented with Fe-Pro M or Fe-Pro ES than for the birds fed the diet supplemented with Fe SO4 or Fe-Met W, and no differences were found between the Fe-Pro M and Fe-Pro ES treatments(P>0.05).(2) The m RNA and protein levels of DMT1 and FPN1 in the duodenum were higher(P < 0.01) than those in the jejunum and ileum. The addition of Fe decreased(P<0.01) the m RNA levels of DMT1 and FPN1 in the duodenum of broilers. No differences were detected(P>0.05) in the m RNA and protein levels of DMT1 and FPN1 in the three intestinal regions among different Fe treatments. The results demonstrated that the duodenum was the main site of gene expressions of DMT1 and FPN1 in the small intestine of broilers, which might be an important cause for the results obtained from the first experiment that the duodenum was a main site of Fe absorption in the small intestine and Fe absortion in the duodenum followed a saturable carrier-mediated process. Furthermore, organic Fe sources with moderate or extremely complex strength showed higher Fe absorption in the samall intestine than Fe sulfate and organic Fe source with weak complex strength, and the DMT1 and FPN1 might be involved in the regulation of Fe transport in the small intestine of broilers.In conclusion, the duodenum was the main site of Fe absorption in the intestines of broilers, and Fe absortion in the duodenum followed a saturable carrier-mediated process. Moreover, the duodenum was the main site of gene expressions of DMT1 and FPN1 in the small intestine of broilers, which might be an important cause for the results that the duodenum was a main site of Fe absorption in the small intestine and Fe absortion in the duodenum followed a saturable carrier-mediated process. In addition, organic Fe sources with moderate or extremely complex strength showed higher Fe absorption in the samall intestine than Fe sulfate and organic Fe source with weak complex strength, and the DMT1 and FPN1 might be involved in the regulation of Fe transport in the small intestine of broilers.