The Roles And Mechanisms Of Methionine Hydroxy Analog Chelated Zinc On Cadmium-induced Intestine Damage And Cadmium Metabolism In Weaned Piglets

This study aims to investigate the mechanism of cadmium metabolism and intestinal injury induced by cadmium in piglets.This research will provide references for repair of intestinal damage caused by cadmium-contaminated feed,which is important for advanced application of minerals in animal husbandry.24 piglets?Landrace×Large white,45 day of age,13.22±1.36 kg BW?were randomly allotted to four dietary treatment?6 piglets per treatment,one piglet per pen?:basal diet?control group,Con?,basal diet+30 mg·kg^-1CdCl₂?as Cd,Cd?,basal diet+30 mg·kg^-1 Cd+100mg·kg^-1 MHZn?as Zn,LMHZn?,basal diet+30 mg·kg^-1Cd+200 mg·kg^-1 MHZn?as Zn,HMHZn?.The trial period lasted 30 days.The results showed that piglets in Cd group had lower ADG,higher F/G ratio,liver coefficient and albumin in plasma compared with Con group?P<0.05?.When piglets were fed with Cd and MHZn together,the ADG was increased,F/G ratio was decreased,and the liver coefficient was decreased compared with Cd group?P<0.05?.On the other side,dietary Cd significantly decreased the villus height of duodenum and jejunum?P<0.05?,increased crypt depth of duodenum and jejunum?P<0.05?,decreased the ratio of C/V?P<0.05?compared with Con group;Hepatocellular degeneration and renal tubular degeneration were observed in Cd group.When piglets were fed with Cd and MHZn together,compared with Cd treatment,MHZn increased the villus height of duodenum and jejunum?P<0.05?,suggesting that it can prevent Cd-induced damage of intestinal villus.Besides,MHZn decreased the granular degeneration and steatosis in liver,reduced renal tubular degeneration and lymphocyte proliferation in kidney.In view of the effect of Cd in damaging the intestinal barrier function,this study further explored the effect of MHZn on small intestinal tight junctions.The results showed that piglets in Cd group decreased the protein expressions of Claudin-1,ZO-1 of duodenum?P<0.05?,as well as Claudin-1,ZO-1 and occlaudin in jejunum?P<0.05?.When piglets were fed with Cd and MHZn together,compared with Cd treatment,the protein expression of ZO-1 in HMHZn was significantly increased?P<0.05?.These results suggested that MHZn is helpful in reliving the Cd-induced damage on liver,kidney and small intestine.The results of determination of cadmium and minerals in piglets showed that,compared with Con group,the concentrations of cadmium in heart,lung,spleen,liver,kidney,muscle,stomach and the jejunum,ileum,caecum,colon,and rectum were significantly increased?P<0.05?.When piglets were fed with Cd and MHZn together,compared with Cd treatment,the concentrations of cadmium in those tissues were significantly decreased?P<0.05?,and the higher the amount of MHZn was added,the lower the Cd was accumulated in the tissues.However,compared with Con group,the concentrations of cadmium in digesta of cecum and colon,along with faeces were significantly increased in other three groups?P<0.05?,When piglets were fed with Cd and MHZn together,compared with Cd treatment,the concentrations of cadmium in digesta and faeces were significantly decreased?P<0.05?.These results suggested that MHZn may increase the absorption level of Cd and reduced its excretion.The research on mRNA expressions of metal elements transports in small intestine showed that,compared with the Con group,Cd significantly decreased the mRNA expressions of ZIP14 and FPN1 in duodenum,increased the TRPV6 expression in jejunum?P<0.05?.The co-treatment of Cd and MHZn significantly increased the expressions of DMT1,ZIP8 in duodenum,ZnT5,TRPV6 and ZIP14 in jejunum.These results indicated that Cd may promote the absorption of Cd through up-regulating the transporters described above.The results of analysis of amino acid transporters showed that Cd significantly reduced the mRNA expressions of y⁺LAT1,LAT2 in duodenum?P<0.05?,the mRNA expressions of y⁺LAT1,LAT2,B0AT1and LAT1 in jejunum?P<0.05?,suggesting that MHZn may promote the absorption of some amino acids by up-regulating the amino acids transporters in piglets co-fed with Cd.The results of serum free amino acids analysis showed that the concentrations of Tau?Asp?Glu?a-AAA?Phe?Lys and His were significantly higher,and the concentrations of Cys was significantly lower in HMHZn group than those in Con,Cd and LMHZn group?P<0.05?.Compared with Cd and LMHZn group,the concentrations of Met?Leu and Tyr were significantly increased and not significant different from Con group?P>0.05?.These results showed that MHZn increased levels of plenty free amino acids in serum,this process may be responsible for the accelerated Cd metabolism.In conclusion,this study found that MHZn can improve the growth performance,alleviate Cd-induced damage and denaturalization of liver and kidney cells,and facilitate to maintain tight junctions of intestinal epithelial cells in piglets co-fed with Cd.In addition,MHZn can significantly reduce the accumulation of Cd in piglets,but increase the absorption of Cd.It indicates that MHZn accelerates the metabolic rate of Cd in piglets,this process may be closely associated with the regulation of expressions of intestinal metal trace elements and amino acid transporters by MHZn,along with the metabolism of amino acids in piglets.