| Cadmium(Cd)and lead(Pb)are ubiquitous in the environment,which can enter the food chain to affect animal bodies.At present,relevant research mainly focuses on the toxicity of a single heavy metal,but there are many kinds of heavy metal pollution in the feed,especially the joint pollution of Cd and Pb is more common.The important toxicity mechanism of Cd and Pb is to cause oxidative damage to organs,and the kidney is their common target organ.Dihydromyricetin(DHM)and α-lipoic acid(α-LA)are antioxidants that can effectively relif the oxidative stress caused by toxins.In this experiment,the combined effect and possible mechanism of Cd and Pb on broiler performance and kidney were studied through animal experiments,and the effect of supplement with DHM and α-LA in the diet to alleviate the combined toxicity of Cd and Pb was explored.Part 1 Effects of dietary Cd and Pb on broiler performance and kidney damageIn the experiment,168 1-day-old Ross 308 broilers were randomly divided into 4groups,with 7 replicates in each group,and 6 chickens in each replicate: control group(basal diet BD),Cd group(50 mg/kg Cd),Pb group(200 mg/kg)and Cd+Pb group(50mg/kg Cd+200 mg/kg Pb).During the experiment,body weight gain and feed intake were recorded,and the ratio of feed to meat was calculated.At the end of the 3rd and 6th week of the experiment,one chicken per replicate in each group was randomly selected for slaughter,and blood,kidney,breast muscle,skin,feather and tibia were collected for the experiment.Results are as follows:1.Effect of the Cd and Pb in diet on the production performance of broilers: At the3 rd week,compared with the control group,the Cd or Pb had no significant(P > 0.05)effect on the production performance of broilers,while the ADFI and ADG in the Cd+Pb group were significantly(P < 0.05)decrease.At week 6,compared with the control group,ADFI in Cd group and Cd+Pb group was significantly(P < 0.05)decreased,and F/G was significantly(P < 0.05)augmented.ADG in the Cd+Pb group was significantly(P < 0.05)decreased.And there were no interaction between Cd and Pb in broilers performance.2.Effects of Cd and Pb on tissue residues and kidney trace elements: Compared with the control group,Cd residues in Cd group and Cd+Pb group were significantly(P < 0.05)augmented,and Cd and Pb interaction in the feathers was significant(P < 0.05);Compared with control group,Pb residues in the Pb group and the Cd+Pb group was significant augmented(P < 0.05).Compared with the control group,the content of Zn and Cu in Cd and Cd+Pb were significantly(P < 0.05)augmented;the content of Mn in Pb group was significantly decreased(P < 0.05).3.Effects of Cd and Pb in diet on broiler kidney damage and tibia indexes: Kidney pathological sections and ultrastructure showed that both Cd and Pb caused damage to broiler kidneys at the 3rd and 6th weeks,and Cd+Pb group was more serious than Cd/Pb group,including augmented renal tubular epithelial degeneration and augmented interstitial congestion points.Serum biochemical indexes showed that at the 3rd week,compared with the control group,the content of TP in the kidneys of the Cd group was significantly(P <0.05)augmented,the content of BUN in the Pb group was significantly(P < 0.05)augmented and the content of BUN,CREA,TG in Cd+Pb group was significantly augmented(P < 0.05),meanwhile,there’s significant interaction of Cd and Pb on CREA and TG.At the 6th week,the BUN in the Pb group was significantly(P < 0.05)augmented,the BUN and CREA in the Cd+Pb group were significantly(P < 0.05)augmented.Compared with the control group,at 3rd week,the CAT activity in the Cd group was significantly(P < 0.05)decreased,the MDA content in the Pb group was significantly(P< 0.05)augmented,the CAT,SOD,T-AOC,GPX activity and MT content in the Cd+Pb group were significantly(P < 0.05)decreased,and the interaction of Cd and Pb on MT in kidney was significant(P < 0.05).At the 6th week,the activities of CAT and T-AOC in the Cd group were significantly(P < 0.05)decrease,and the activity of CAT in the Pb group significantly decreased(P < 0.05),the activities of CAT,T-AOC,and GPx in the Cd+Pb group were significantly decreased(P < 0.05).In the sixth week,the Ca content of the tibia was significantly(P < 0.05)decrease in the Cd+Pb group than in the control group.Also,it can be seen from the TUNEL results that the combined exposure of Cd and Pb will cause more severe renal cell apoptosis.4.Effect of Cd and Pb in diet on PERK-ATF4 in broiler kidney: Compared with the control group,the m RNA expression of Mfn2 in the Cd group and Pb group was significantly(P < 0.05)down-regulated,and the expression of ATF4 and MT was significantly(P < 0.05)up-regulated,aslo in the Cd+Pb group,Mfn2 was significantly(P< 0.05)down-regulated,the expressions of GRP78,PERK,ATF4 and CHOP were significantly(P < 0.05)up-regulated.And the interaction of Cd and Pb on the expression of Mfn2,GRP78 and PERK was significant(P < 0.05).Part 2 The detoxification effect of DHM and α-LA on the kidney under the combined effect of Cd and Pb.In the experiment,168 one-day-old Ross 308 broilers were randomly divided into 4groups,with 7 replicates in each group and 6 chickens in each replicate.Control group(basal diet),Cd group(50 mg/kg Cd),Pb group(200 mg/kg),Cd+Pb group(50 mg/kg Cd+200 mg/kg Pb),DHM group(50mg/kg Cd+200mg/kg Pb+600 mg/kg DHM)and α-LA group(50 mg/kg Cd+200 mg/kg Pb+400 mg/ kg α-LA).Sampling,from slaughtered broilers in the 3rd and 6th week of the experiment,and the results are as follows:1.Effect of DHM and α-LA in the diet on the production performance of broilers: At the 3rd week,compared with the control group,the production performance of broilers in DHM and α-LA group showed no obvious change.At the 6th week,the ADG and ADFI of the DHM group and α-LA group were significantly(P < 0.05)lower than the control group,ADFI was significantly(P < 0.05)higher than the Cd+Pb group.2.Effect of DHM and α-LA in the diet on broiler residues and trace elements in kidneys: supplement with DHM and α-LA had no significant effect on Cd/Pb residues in tissues.Compare with control group,the Cu and Zn content in kidneys of DHM and α-LA group were significantly higher(P < 0.05),meanwhile the Zn content in DHM group was significantly(P < 0.05)lower than Cd+Pb group.3.Effect of dietary supplementation of DHM and α-LA on kidney damage caused by Cd and Pb: The results of pathology and ultra-electron microscopy showed that the addition of DHM and α-LA could alleviate the kidney damage under the combined exposure of Cd and Pb at the 3rd week.Serum biochemical results showed that compared with Cd+Pb group,the contents of BUN,CREA and TG in DHM and α-LA group were significantly(P< 0.05)lower,in addition,BUN and TP were not significantly different from control group.At 6th week,compared with Cd+Pb group,contents of BUN and TG in the DHM and α-LA group were significantly(P < 0.05)lower,as well as there were no significant change compare with control group.At the same time,at the 3rd week,compared with the Cd+Pb group,CAT and SOD activity in DHM and α-LA group of broilers were significantly(P <0.05)augmented.While compared with control group,the activity of T-AOC,GPx and MT content of the DHM group was significantly(P < 0.05)decrease,and the T-AOC in α-LA group was significantly decrease.At the 6th week,compared with the Cd+Pb group,the activities of CAT,T-AOC and GPx in DHM group and α-LA group were significantly(P< 0.05)augmented and there’s no significant change compared with control group.The Ca content of the tibia in the DHM group was significantly(P < 0.05)lower than that in the control group.The TUNEL results showed that the addition of DHM and α-LA could alleviate the increase of renal apoptotic cells caused by the Cd and Pb.4.Effects of dietary supplementation with DHM and α-LA on PERK-ATF4 pathway:Compared with the Cd+Pb group,the GRP78,PERK and e IF2α in DHM group were significantly down-regulated(P < 0.05)and GRP78,PERK,e IF2α and ATF4 were significantly down-regulated(P < 0.05).Compared with the comtrol group,the m RNA levels of Mfn2 in the DHM and α-LA groupsw as significantly(P < 0.05)down-regulated,the m RNA levels of GRP78,PERK and e IF2α in DHM group were significantly(P < 0.05)lower,and the m RNA levels of CHOP was significantly(P < 0.05)up-regulated,,the m RNA expression of Mfn2 and e IF2α in the α-LA group was significantly(P < 0.05)downregulated,and the m RNA expressions of ATF4 and CHOP were significantly(P < 0.05)up-regulated.Conclusions: 1)Cd and Pb reduce the performance of broilers,and the addition of DHM and α-LA for six weeks can alleviate the effects of combined Cd and Pb exposure on performance;2)Cd and Pb in broiler tissues The order of residues from high to low is:kidney>feather>skin>pectoralis muscle and feather>kidney>skin>pectoralis muscle;3)The combined effects of Cd and Pb aggravate the oxidative damage of broiler kidneys,which may be due to the increase of PERK-ATF4 pathway genes.Supplement with DHM and α-LA can increase the activity of antioxidant enzymes and augmented the expression of PERK-ATF4 pathway gene to alleviates oxidative damage. |
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