Effects Of Low-levels Of Organic Trace Minerals Substitution On Production,egg Auality And Trace Mineral Metabolism Of Laving Hens

The objective of this study was to investigate the effects of low inclusion levels of organic trace minerals(iron,copper,manganese,and zinc)on productive performance,egg quality,physiological,biochemical and trace mineral metabolism of Hy-Line White laying hens during the late laying period.There were 3 dietary treatments,and each treatment had 9 replications with 15 birds per replication.The dietary treatments included a basal diet supplemented with inorganic trace minerals at commercial levels(CON;Fe,Cu,Mn,and Zn at 36,12,90,and 90 mg/kg,respectively),a basal diet supplemented with inorganic trace minerals at 1/3 commercial levels(ITM),and a basal diet supplemented with proteinated trace minerals at 1/3 commercial levels(TRT).The trial lasted for 56 days.The major results were as follows:1.Effects of organic trace minerals on the performance,immunity and antioxidant functions of laying hens1)Compared with the CON group,the ITM group showed decrease in egg production and daily egg mass,and increase in feed to egg ratio(P<0.05).Compared with the ITM group,the TRT group showed increase in egg production and daily egg mass(P<0.05),and decrease in feed to egg ratio(P<0.05);2)Compared with the CON group,the UA content,ALT and AST activities in serum of ITM group were increased(P<0.05),while AKP activity was decreased(P<0.05).The TRT group had higher AKP activity,and lower UA content,ALT and AST activities(P<0.05)in serum,compared to ITM group;3)Compared with the CON group,the TP content in serum of ITM group was decreased(P<0.05).The TRT group had higher serum TP content compared to ITM group;4)Compared with the CON group,serum T-AOC、T-SOD、Mn-SOD and GSH-Px activities in ITM group were decreased(P<0.05),and serum MDA content was increased(P<0.05).The TRT group had higher serum T-AOC、T-SOD、Mn-SOD and GSH-Px activities(P<0.05),and lower serum MDA content(P<0.05)compared to ITM group;5)Compared with the CON group,hepatic T-SOD,Cu/Zn-SOD and Mn-SOD activities were decreased(P<0.05)in ITM and TRT group,and hepatic GSH-Px activity was decreased(P<0.05)in ITM.The MDA hepatic content of TRT group was lower compared to CON and ITM group(P<0.05).2.Effects of organic trace minerals on egg quality,egg-producing hormone levels and enzyme activities1)Compared with the CON group,the albumen height and eggshell strength were decreased(P<0.05),and egg loss was increased in ITM group(P<0.05).The TRT group had higher eggshell strength and lower egg loss(P<0.05)compared to ITM;2)Compared with the CON group,the total thickness,eggshell palisade layer and palisade layer ratio were decreased(P<0.05),and mammillary layer ratio was increased(P<0.05)in ITM group.The total thickness,eggshell palisade layer and palisade layer ratio were higher(P<0.05)in TRT compared to ITM group.What’s more,the TRT group had smaller mammillary knob width(P<0.05)compared to CON and ITM group.In addition,the ITM group showed obvious cracks on the cross section and outer surface of the eggshell;3)Compared with the CON group,the ITM group showed decrease in E and LH levels,CA activity,and GAG and Ca contents(P<0.05)in serum.The TRT group had higher E and LH levels,CA activity,and GAG content(P<0.05)in serum compared to ITM;4)There were no significant differences in the contents of Fe,Cu,Mn,Zn,Ca,and P of eggshell in three group(P>0.05).3.Effects of organic trace minerals on trace mineral metabolism,trace mineral related protein contents,enzyme activities and metallothionein expression in laying hens1)Compared with the CON group,the contents of serum Fe and Mn,and yolky Fe in ITM were decreased(P<0.05).The contents of serum Mn and yolky Fe in TRT were higher compared to ITM group(P<0.05);2)Compared with the CON group,the contents of hepatic Fe,Mn and Zn,cardiac Mn,and splenic Fe and Zn in ITM group were all decreased(P<0.05).The contents of hepatic Fe and Mn,and cardiac Mn in TRT group were higher than those in ITM group(P<0.05);3)Compared with the CON and TRT group,tibial Mn and Zn were decreased in ITM group(P<0.05).Compared with the CON group,both ITM and TRT reduced(P<0.05)fecal mineral excretion.In addition,TRT group had lower fecal Cu,Mn and Zn excretion than those in ITM group(P<0.05);4)Compared with the CON and TRT group,the serum TRF level in ITM was increased(P<0.05).There was no significant difference in the content of serum CER level in three group(P>0.05).Compared with the CON and TRT group,the cardiac Cu/Zn-SOD activity in ITM group was decreased(P<0.05).Compared with the CON group,the hepatic and duodenal AKP activities were decreased(P<0.05)in ITM group.The hepatic AKP activities in TRT group was higher(P<0.05)than that in ITM group;5)Compared with the CON and TRT group,the mRNA expression of MT gene in liver and jejunum in ITM group were decreased(P<0.05).In conclusion,under the conditions of this experiment,the low levels of inorganic trace minerals would have negative effects on the productive performance,egg quality and trace mineral metabolism of laying hens.However,the addition of low levels of protein chelated iron,copper,manganese and zinc completely replace their inorganic forms to the diet of laying hens at the late laying period,can achieve the effect similar to that of inorganic trace minerals at the commercial levels.The low levels of organic trace minerals can maintain the normal physiological and biochemical metabolism,improve the eggshell ultrastructure and the egg quality,and ensure the productive performance of the laying hen at late laying period,and significantly reduce the excretion of the same trace minerals in the feces.They have higher absorption efficiency and bioavailability than inorganic trace minerals at the same low levels.