| Iron is one of the essential trace elements in animal life and growth.In livestock production,the addition of exogenous iron in feed,especially inorganic iron,has long been used in breeding industry.However,due to the low utilization rate of inorganic iron,it often lead to the waste of trace elements resources and cause environmental pollution in actual production.While inorganic iron is likely to cause oxidative stress to the body,affecting animal growth performance.Iron amino acid chelate belongs to the third generation of trace element additives,the iron ion binding with amino acid to form an annular structure,thus it is high bioavailability,good chemical stability,conducive to environmental protection.Ferrous glycinate is a kind of amino acid chelated iron with glycine as the ligand.Because glycine is the smallest molecular weight amino acid,ferrous glycinate is more easily absorbed in vivo.Heme iron is obtained from animal products,which can be directly absorbed in the form of porphyrin,often used to treat human iron deficiency anemia.At present,there are many applied research of ferrous glycinate,but the application of heme iron in animal production is relatively few,and lack of the comparative of different iron sources.In addition,recent researches demonstrated that there are differences in the absorption efficiency of ferrous sulfate and ferrous glycinate,but the concrete mechanisms are still not very clear.Therefore,in this study,weaned piglets and SD rats are used to investigate the effect of ferrous sulfate,ferrous glycinate and heme on body iron status and their absorption characteristics in intestine,mainly studied the absorption mechanism of ferrous glycinate,to further enrich the absorption and transport theory of organic iron,elucidate the absorption mechanism of different iron sources.The main results are as follows:1.The effects of different iron sources on body iron metabolism of piglets and their impacts on related transporters32 healthy piglets were randomly allotted to 4 groups,and the control group was fed with basal diet(no extra iron added).On the basis of the control group,three experiment groups were added with ferrous sulfate,ferrous glycinate and heme(100 mg Fe/kg).The feeding experiment lasted 28 days,and effects of different iron sources on growth performance,body iron status,meat color and intestinal morphology of weanling piglets were studied.The results showed that the addition of three different iron sources could significantly increase the average daily gain(P<0.05)in the late feeding period(14～28 d),but not the early feeding period(1～14 d)and the whole feeding period(1～28 d).Compared with other groups,the addition of heme in feed can significantly improve myoglobin content in muscle,thus increased the meat color of longissimus dorsi(P<0.05).At the 28th day,ferrous glycinate and heme significantly increased the serum iron content of weaned piglets(P<0.05),and the iron deposition of ferrous glycinate and heme in the liver was also significantly increased(P<0.05).This shows that the two iron sources as organic iron,the absorption and utilization are better than ferrous sulfate,and can effectively improve the body iron status of piglets.In addition,all iron supplementation groups significantly increased the villus height of duodenum and jejunum when compared with the control group(P<0.05),indicating that iron plays a very important role in intestinal morphology development.However,there were no significant differences in hepcidin level of serum and liver between these groups,indicating that the iron homeostasis of piglets was not affected by the iron source in the feed.The IPEC-J2 cell model was successfully established to study different concentrations of ferrous sulfate and ferrous glycine on cell proliferation.Meanwhile,the effects of ferrous sulfate and ferrous glycinate on the expression of iron metabolism related genes were also studied.The results show that two kinds of iron source in low concentration has no obvious effect on cell growth,but when iron concentration is high,they can cause significant cytotoxicity,and ferrous sulfate has greater impacts to cells than ferrous glycinate.Related genes expression results suggest that in the same concentration,ferrous sulfate has more free iron ions than ferrous glycinate,two iron sources may have the same absorption process.2.The absorption characteristics and absorption mechanism of different iron sources in SD rats32 SD rats were randomly allotted to 4 groups,gavage with normal saline,ferrous sulfate,ferrous glycinate and heme solution(80 mg Fe/L)everyday,1.5 mL each time.The effects of different iron sources on body iron status and antioxidant capacity of rats were studied.In addition,another 16 SD rats were slaughtered and the duodenum samples were used to conduct Ussing Chamber experiment.The results show that three kinds of iron sources can increase serum iron content and the deposition of iron in duodenum,improve the body iron status,but effects of ferrous glycinate are the best(P<0.05).Ussing Chamber results indicate that,iron plays a role in maintain the integrity of intestinal barrier,and ferrous sulfate and ferrous glycinate may have the same absorption process.24 SD rats were randomly allocated into 2 groups,administered with ferrous sulfate and ferrous glycinate solution(80 mg Fe/L),1 mL each time,the experiment lasted for two weeks.At the end of the experiment,duodenum samples were collected for total RNA extraction,and then RNA-seq was performed by Illumina Hiseq 2500 sequencing platform.The results show that the ferrous glycinate can increase serum iron content,transferrin saturation,and liver ferritin deposition(P<0.05),indicate that ferrous glycinate can be better and faster absorbed than ferrous sulfate.However,high-throughput sequencing results show that intragastric administration of different iron sources don’t affect the expression of intestinal iron related transport protein,and the selected differential expression genes are more likely to linked with glycine ligand or iron content in cells.Our study indicates that,ferrous sulfate and ferrous glycinate have the same intestinal absorption process,both are absorbed by intestine through inorganic iron ion.The bio-availability differences of two iron sources may be mainly due to the different absorption efficiency in intestine.In summary,the addition of iron source in diets can improve growth performance,body iron status,and intestinal morphology development of piglets.Consider from absorption and utilization aspects,ferrous glycinate and heme as organic iron exhibited better bio-availability.The cytotoxicity of ferrous glycinate is smaller than ferrous sulfate.In same concentration,ferrous sulfate have more free iron ions than ferrous glycinate.Both of the two iron sources are absorbed by intestine through inorganic iron ion,their bio-availability differences may be mainly due to the different absorption efficiency in intestine. |
