Effect Of Different Zinc Sources And Levels On Blood Biochemical Indexes, Tissue Zinc Concentration And Correlative Gene Expres Sion Of Growing-finishing Pigs

This experiment aimed to evaluate the effects of low levels of zinc methionine?Zn-Met?or zinc sulfate?ZnSO₄?on growth,serum physiological and biochemical indexes,serum antioxidant index,apparent absorptivity of trace elements,tissue zinc concentration and correlative gene expression to determine the appropriate level of zinc addition in the diet for growing-finishing pigs,to realize the effective utilization of resources and reduce the environmental impact of zinc in excreta,in order to provide theoretical basis for the suitable addition of zinc in the stage of growing-finishing pigs.Thirty-two growing-finishing pigs?Duroc×Landrace×Largewhite?with average weight of?33.70±2.76?kg were randomly divided into 4 groups with 8 replicates?1 pig per replicate?.The control group was fed a basal diet,while experimental groups?group 1,group2 and group 3?were added 40 mg/kg zinc?zinc methionine?,40 mg/kg zinc?zinc sulfate?and80 mg/kg zinc?zinc sulfate??calculate by zinc?,respectively.There was a 7-day adaptation period and a 72-day experimental period.In addition,the experimental period was divided into two stages of 30-60 kg and 60-90 kg.The results showed as follows:?1?Compared with the basal diet group,there were no significant differences on average daily gain weight,average daily feed intake and feed weight ratio,apparent digestibility of CP and EE of growing-finishing pigs with different zinc sources and levels?P>0.05?.?2?Compared with the control group,dietary supplementation with Zn-Met or ZnSO₄ significantly increased the content of WBC and LYM in serum,the content of TP and ALB in serum,the activity of ALP,the activity of T-SOD,GSH-Px and CuZn-SOD in serum?P<0.05?;whereas dietary supplementation of Zn-Met or ZnSO₄remarkably decreased the content of BUN,the activity of ALT,AST,LDH in serum,and the content of MDA?P<0.05?.Besides,group with 40 mg/kg Zn-Met got the highest WBC and LYM content,TP and ALB content,ALP activity,T-SOD and GSH-Px activity in serum and the lowest BUN content,ALT?AST and LDH activity,MDA content in serum.While the activity of serum CuZn-SOD increased with the addition of ZnSO₄,and the activity was highest in 80 mg/kg ZnSO₄ group.?3?Compared with the basal diet group,the addition of Zn-Met in diets significantly increased the apparent absorptivity of Zn,Cu and Mn?P<0.05?,while the addition of ZnSO₄ only significantly increased the apparent absorptivity of Zn and decreased with the addition of ZnSO₄?P<0.05?,the apparent absorptivity of Zn in the 40mg/kg Zn-Met group was the highest.?4?Compared with the basal diet group,dietary supplementation of Zn-Met significantly increased Zn content in serum?P<0.05?,and dietary with 40 mg/kg Zn-Met got the highest Zn content in serum;No significant differences of Zn content were observed in spleen,pancreas,hair and muscle of growing-finishing pigs?P>0.05?,while dietary supplementation of Zn-Met or ZnSO₄ significantly increased Zn deposit in liver and bone?P<0.05?.?5?Compared with the control group,dietary supplementation with Zn-Met or ZnSO₄ significantly increased the relative expression of MT-1 mRNA in the liver,pancreas and duodenum?P<0.05?;besides,group with 40 mg/kg Zn-Met got the highest relative expression of MT-1 mRNA in the liver,pancreas and duodenum;dietary supplementation with Zn-Met or ZnSO₄ only significantly increased the relative expression of CuZn-SOD mRNA in the liver?P<0.05?,while had no significant effect on the relative expression of CuZn-SOD mRNA in the pancreas and duodenum?P>0.05?.Based on the current results,dietary supplementation with Zn-Met or ZnSO₄significantly improved serum physiological and biochemical indexes,antioxidant index and apparent absorptivity of trace elements,the content of zinc in serum,zinc deposition in liver and bone and the relative expression of mRNA in tissues for growing-finishing pigs.It is concluded that 40 mg/kg Zn-Met is better than the same level of 40 mg/kg ZnSO₄ and the higher level 80 mg/kg ZnSO₄ in the experimental condition.