Study On Different Zinc Sources In Modulating Mechanisms Of Reducing Incidence Of Diarrhea Of Weaned Piglets

Three experiments in this study were conducted to study applications of tetrabasic zinc chloride(TBZC)and nano zinc oxide(nano-ZnO)in weaned piglets and to explore the mechanisms of reducing incidence of diarrhea.In Exp.1,one hundred and eighty Large White × Landrace × Duroc weaned piglets(initial body weight 8.92±1.05 kg)were randomly divided into 5 treatments with 6 replicates and fed corn-soybean meal basal diets supplemented with 0,1,200,1,800,2,400,and 3,000 mg/kg Zn as TBZC for consecutive 28 days.Results showed that TBZC inclusion in diets linearly(P<0.05)and quadratically(P<0.05)elevated ADG during post-weaning d 0～14 and 0～28 and G:F during post-weaning d 0～14 of weaned piglets,linearly(P<0.01)and quadratically(P<0.01)decreased incidence of diarrhea during post-weaning d 0～14,15～28 and 0～28.On post-weaning d 28,incremental TBZC linearly(P<0.05 or P<0.01)increased haemoglobin level,serum concentrations of alanine aminotransferase and alkaline phosphatase,dudenual villus height and villus height:crypt depth,liver and kidney indexes,and the number of lactic acid bacteria and total anerobic bacteria in the jejunal and ileal digesta,linearly decreased(P<0.05)the population of E.Coli in the cecal and colonic contents,and manganese level in fibula,quadratically changed(P<0.05)ADG and G:F during post-weaning d 15～28,jejunal villus height,total antioxidant capacity,malondialdehyde content and glutathione peroxidase activity in liver.In Exp.2,two hundred and sixteen Large White × Landrace × Duroc weaned piglets(initial body weight 8.88±1.14 kg)were randomly assigned to 1 of 6 treatments with 6 replicates(pens)per treatment and fed corn-soybean meal basal diet supplemented with 2,000 mg/kg Zn as ZnO,and 0(control),300,400,500 and 600 mg/kg Zn as nano-ZnO for 14 days,selected piglets(n =36,one piglet per pen)were euthanized on d 14 and the remaining piglets were all fed the same control diet during d 15～28.Results showed that increased nano-ZnO supplementation linearly improved(P<0.01 or P<0.05)ADG during post-weaning d 0-14 and 0～28,and serum insulin level,liver concentrations of superoxide dismutase and metallothionein,as well as lactic acid bacteria number,concentrations of acetic acid and total volatile fatty acids in the ileal and cecal digesta,linearly and quadratically increased(P<0.01 and P<0.05)serum levels of IgG,superoxide dismutase and total anerobic bacteria number in the cecal content,linearly decreased(P<0.05 or P<0.01)serum malondialdehyde content and total aerobic bacteria on post-weaning d 14,linearly and quadratically decreased(P<0.05 and P<0.01)incidence of diarrhea during post-weaning d 0～14 and 0～28 and liver malondialdehyde level on d 14.Notably,there were no significant differences between piglets fed 600 mg/kg Zn from nano-ZnO and 2,000 mg/kg Zn as ZnO in these mentioned parameters(P>0.05).In Exp.3,one hundred and forty-four Large White × Landrace × Duroc weaning piglets(initial body weight 7.40± 0.84 kg),were randomly assigned to 1 of 4 treatments with 6 replicates per treatment and fed corn-soybean meal basal diet supplemented with 0(control),1,800 mg Zn/kg as TBZC,600 mg Zn/kg as Nano-ZnO and 2,000 mg Zn/kg from ZnO for 14 days.Results showed that compared with the control treatment,dietary supplementation with 1,800 mg Zn/kg as TBZC and 600 mg Zn/kg from nano-ZnO both significantly decreased the incidence of diarrhea of weaning piglets during post-weaning d 0～14,mRNA expressions of IFN-γ,IL-β,IL-6,TNF-α and NF-κB,and bacterial diversity in the colonic digesta(P<0.01 or P<0.05),increased villus height:crypt depth and mRNA expressions of Cu-Zn SOD,GPX1,ZO-1,Occludin,CDK4 in jejunum,and relative abundance of Firmicutes and Lactobacillus(P<0.01 or P<0.05).There were no significant differences in villus height,villus height:crypt depth,mRNA expressions of ZO-1,CDK4 and Caspase3 in jejunal tissue,IFN-y mRNA expression in ileal tissue,richness of bacteria and core microbiota in cecal digesta among treatments of 2,000 mg Zn/kg as ZnO,1,800 mg Zn/kg from TBZC and 600 mg Zn/kg from nano-ZnO(P>0.05).In conclusion,this study indicates that dietary supplementation with 1,200～1,800 mg Zn/kg as TBZC for 28 days can improve growth and diarrhea incidence of weaned piglets,while over 2,400 mg Zn/kg as TBZC may cause a mild toxicity;in addition,600 mg Zn/kg as nano-ZnO inclusion in diet may has a potential function comparable to 2,000 mg Zn/kg from ZnO in promoting growth and reducing diarrhea incidence of weaned piglets;TBZC and nano-ZnO can alleviate diarrhea incidence probably by promoting intestinal development,antioxidant status and barrier function,inhibiting expressions of pro-inflammatory cytokines,and modulating bacterial richness and diversity in intestinal tract.