Effect Of Cadmium On The Performance And Ovary Of Laying Hens And The Alleviating Effect Of Selenium On Cadmium

With the development of modern chemical agriculture,cadmium?Cd?pollution has become an increasingly common environmental problem.Cd can be accumulated in animals and plants through soil,water and air,resulting in damage to the reproductive system of poultry,poor performance,and accumulation of Cd in eggs,which poses a great threat to food safety and human health.Selenium?Se?can reduce the toxicity of Cd in animals.In this study,laying hens in peak stage were randomly divided into four groups,the control group,Se group,Cd group,and Se+Cd group.In the control group,chickens were fed a basic diet containing 0.2 mg/kg Se and 0.08mg/kg Cd.The Se-treated group was fed a basic diet supplemented with 2 mg/kg of Na₂SeO₃,the Se+Cd treated group was fed a basic diet supplemented with 150 mg/kg of CdCl₂ and 2 mg/kg of Na₂SeO₃,and the Cd-treated group was fed a basic diet supplemented with 150 mg/kg of CdCl_2.And then,the performance,egg quality,ovarian morphology,serum estradiol,oxidant and antioxidant indices,28 ionic concentrations and apoptosis genes were detected for the study of reproductive toxicity of Cd and the antagonism of Se in the laying hens.The research may provide a theoretical basis for the prevention and treatment of Cd poisoning and improve the knowledge of environmental pollutants and their antagonists,00as well as the interaction mechanism between them.The results showed that the egg production,egg mass and feed intake of the Cd group were significantly lower than that of the control group?p<0.05?while these parameters in the Se+Cd group were significantly higher than that in the Cd group.Feed conversion ratio of the Cd group was significantly higher than that of the control group?p<0.05?,while the Se+Cd group was slightly lower than the Cd group?p>0.05?.There was no significant difference between the Se group and the control group for these detected parameters?p>0.05?.Egg weight in the four groups showed no significant difference?p>0.05?.For egg quality,the results showed that the eggshell and egg yolk color were markedly lower in the Cd group than in the control group?p<0.05?,and there was a decrease for the eggshell thickness,albumen height and haugh unit in the Cd group compared with the control group?p<0.05?.While the indices in the Se+Cd group were better than that in the Cd group,and there was no significant change between the Se and the control groups?p>0.05?.But the eggshell strength and egg-shape index have no evident change between the four groups?p>0.05?.Se could partially alleviate the damage to the structure and function of the ovary.Through the observation on HE and ultrastructure of the ovary,we found that there were atretic follicles in the Cd group and the number of the primary as well as developing follicles were dramatically reduced.The nucleus crinkled with irregular shape,and the mitochondria was swollen and endoplasmic reticulum was dilated markedly.The morphology and ultrastructure of the ovarian cells in the Se+Cd group were damaged,but the degree was lower than the Cd group.The results of the control and Se groups were similar.The serum estradiol content in the Cd group was significantly lower than that in the control and Se groups?p<0.01?,and the Se+Cd group was significantly higher than the Cd group?p<0.05?.The difference was not significant between the Se+Cd,Se and control groups?p>0.05?.The concentrations of Ca,Ti,Cu,Zn,and Ba of ovary were significantly reduced in the Cd group than that in the control group?p<0.05?,and Fe,Mo,and Cd were increased remarkably?p<0.05?.In the Se+Cd group,the concentrations of Cu and Se were increased evidently when compared with the Cd group?p<0.05?.In eggs,Cd supplementation significantly decreased the concentrations of Li,Al,Cr,Mn,Ni,Zn,As,Se,Sr,Sn,Hg,and Tl?p<0.05?,while increased the Cd content evidently?p<0.05?.Compared with the Cd group,the concentrations of Mg,Se,and Ba were increased significantly in the Se+Cd group?p<0.05?,while the content of Cd and Pb were decreased?p<0.05?.Se can reduce the adverse effect of Cd on ovarian toxicity and egg quality by rebalancing the concentrations of Cu,Se,Mg,Ba,Cd,and Pb.Se can reduce the toxicity of Cd to ovary through regulating the expression of apoptotic genes and maintaining the balance of oxidative and antioxidant systems.The content of MDA and the activity of GPx in the ovary were significantly different between the control and Cd groups?p<0.01?,while the content of H₂O₂ and the activity of SOD were significantly different between the control and Cd groups?p<0.05?.Compared with the Cd group,the content of MDA and H₂O₂decreased?p>0.05?,and the activity of SOD and GPx increased slightly in the Se+Cd group?p>0.05?.The content of MDA and H₂O₂,and the activity of SOD in the Se group were indifferent from that in the control group?p>0.05?,while the activity of GPx was higher than the control group?p<0.05?.In the Cd group,the MDA content in egg yolk was higher than the control group?p<0.01?,but the GPx activity significantly decreased?p<0.01?.The content of MDA has no difference between the Se+Cd and Cd groups?p>0.05?,while the GPx activity in the Se+Cd group was higher than the Cd group?p<0.05?.The content of MDA decreased?p<0.05?,and the activity of GPx increased?p<0.01?in the Se group than the control group.Cd treatment remarkably increased the expression of P53,Caspase9,Cyt-C,and Bax?p<0.05?in the ovary,while decreased the expression of Bcl-2?p<0.05?.In the Se+Cd group,the expression of Caspase9,Cyt-C,and Bax were lower than the Cd group significantly?p<0.05?and P53 slightly was lower?p>0.05?,while the Bcl-2 was higher than the Cd group?p>0.05?.Except for the high expression of Bcl-2 in the Se group?p<0.05?,there was no significant difference in the expression level of other genes between the control and Se groups?p>0.05?.Therefore,Cd poisoning can reduce the performance and egg quality of laying hens,bring the damage of ovarian cells in the morphology and ultrastructure,reduce the serum estradiol,destroy the ion balance of the ovaries and eggs,reduce the antioxidant capacity and induce cell apoptosis.Se can improve the perfoamance and allivate the ovarian damage casused by Cd through improving antioxidant capacity,regulating cell apoptosis and reconstructing ionic balance.