| The pharmacological dose of ZnO,together with in-feed antibiotics,had been widely used in pig diet,however,it is rarely reported that the effects of replacing both antibiotics and zinc oxide by live yeast on growth,diarrhea severity,intestinal and immunological function.This study aimed to investigate the effects of dietary live yeast(Saccharomyces cerevisiae Sc47;Actisaf(?),Lesaffre Phlieo Animal Care,France)supplementation on growth performance and immunological parameters of piglets challenged with enterotoxigenic Escherichia coli.A total of 180 weaned piglets(6.39±0.05 kg)were randomly allocated into 5 treatments with 6 pens and 6 piglets(3 barrows and 3 gilts)per pen,receiving the control(CON)diet,diets supplemented with antibiotic plus ZnO(ANT-ZnO,20 mg/kg Colistin,75 mg/kg Aureomycin and 2100 mg/kg of ZnO),live yeast at 1(LY1),2.5(LY2.5)or 5 g/kg(LY5)Actisaf(?)(Saccharomyces cerevisiae Sc47 107 cfu/g feed),for a period of 2 weeks.On day 8,six piglets from CON group received sterilized Luria Broth as control(n=6),while another 30 piglets from CON,antibiotic plus ZnO,LY1,LY2.5 and LY5 groups,were were orally challenged with 100 mL of Luria Broth containing 109 of ETEC strain(serotype 0149:K91:K88ac,China Veterinary Culture Collection Center,Beijing,China).Diarrhea scores were daily recorded at 0,6,12,24 and 36 h after ETEC challenge.Body weights and pen feed disappearance were recorded weekly to determine average daily gain(ADG),average daily feed intake(ADFI)and the ratio of ADFI to ADG(F:G).On d 10,blood,urine,spleen,ileum and mesenteric lymph node(MLN)tissue and content samples were collected at necropsy and analyzed for intestinal morphology,mucosal barrier function,intestinal microbial flora and immunological parameters.(1)Piglets in ANT-ZnO group had higher(P<0.05)ADG and ADFI during the first week than those in CON,LYland LY5 group.Moreover,piglets inANT-ZnO group had higher(P<0.05)ADG during the second week than those in CON,LY2.5 and LY5 group.(2)ETEC challenge significantly increased(P<0.05)diarrhea scores,intestinal permeability,Escherchia coli numbers in colon content,decreased(P<0.05)the villus height in jejunum and ileum,the protein expression level of Claudin-1 in ileal mucosa,the numbers of both lactobacillius of piglets in CON group relative to the non-challenged piglets,however,the piglets with ANT-ZnO-ETEC or LY-ETEC had markedly higher(P<0.05)villus height in ileum and lower(P<0.05)diarrhea scores,intestinal permeability and Escherchia coli numbers in colon content relative to piglets with CON-ETEC.Interestingly,piglets in ANT-ZnO-ETEC group markedly decreased(P<0.05)numbers of lactobacillius.Moreover,the counts of laetobaeillus in piglets with LY1-ETEC was markedly higher(P<0.05)than piglets in CON-ETEC and ANT-ZnO-ETEC groups.(3)Compared with the non-challenge piglets,the piglets with CON-ETEC significantly had increased(P<0.05)plasma concentration of Pig Major Acute Phase Protein(pig-MAP)and interleukin-6(IL-6),decreased(P<0.05)plasma concentration of immunoglobulin A(IgA),up-regulated(P<0.05)the mRNA abundances of Toll-like receptor signaling pathway key genes such astoll-like receptor 4(TLR-4),toll-like receptor 9(TLR-9),myeloid differentiation factor 88(MyD88),tumor necrosis factor receptor-associated factor 6(TRAF-6)and IL-6 in ileum and MLN(TLR-4,NF-κB,IL-1β).However,piglets with LY5-ETEC had decreased plasma concentration of pig-MAP and IL-6,also down-regulated the mRNA abundances of key genes as mentioned up-related to the toll-like receptor signaling pathway,which had similar values as that in piglets receiving ANT-ZnO-ETEC.Histopathologically,the piglets with CON-ETEC had obvious neutrophil infiltration,decreased periarterial lymphatic sheath cells in the spleen(5/6 vs.1/6,P=0.08),piglets in ANT-ZnO-ETEC or LY-ETEC group had decreased abnormal histopathology spleen than that of piglets with CON-ETEC.In conclusion,the observations in the current study indicate that ETEC challenge induced diarrhea,impaired intestinal morphology,barrier function and immune system.Feeding pharmacological dose of ZnO,together with in-feed antibiotics diet(ANT-ZnO)could enhance growth performance and alleviate intestinal and immunological functions of piglets challenged with ETEC,however,the replacement of ANT-ZnO with different dose of live yeast in diets had similar effects on growth,intestinal and immunological functions,particularly the higher inclusion of live yeast(LY5)in diet prevented the negative effects of ETEC challenge on immunological and inflammatory responses. |
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