| Salmonella has always been one of the key pathogens for the prevention,control and eradication of breeding company in China.However,with the constantly emergence of antibiotic residues and drug-resistant bacteria,especially the multi-drug resistance(MDR)of Salmonella has increased,make it more difficult to prevent and treat of avian salmonellosis.Therefore,as an antibiotic substitute,selected yeast fraction(SYF)has a broad application prospect as a green and efficient new feed additive for poultry production.The purpose of this investigation is to detect possible Salmonella contaminated in different stages of production within the breeding companies in Guangxi,and the dominant serotypes and drug resistance characteristics of the Salnmonella isolates,and to provide scientific evidence for the prevention and control of avian salmonellosis.Through the laboratory challenge experiment and field trail,a study was carried out to explore the potential application of SYF for the control of the Salnmojnella dominant serotypes Salnmonella pullurom(SP)and Salmoinella gallinarum(SG)in the field by investigating the effects of SYF on the anti-infection,body weight gain against the challenges,and also comparing with the effects of organic acids product.During 2018,totally 1 045 samples including shell surface of hatching eggs at different phases(pre-disinfection,post-disinfection and piped),dead embryos in the late phage of incubation,day-old defective chicks,pullorum disease-fowl typhoid(PD-FT)antibody positive ancd negative hens were collected from 4 chicken breeding companies located in Nanning,Yulin and Liuzhou,respectively.Samples of different internal organs and cloaca swabs were taken from day-old defective birds,PD-FT antibody positive and negative breeding hens,and the liver were collected from the dead embryos.Refer to the National Food Safety Standard,Food Microbiological Examination:Salmonella(GB4789.4-2016)and combine the PCR detection method developed in the laboratory,all the samples were performed Salmonella isolation and identification,and further the Salmonella isolates were serotyped with the Salmonella reference serotyping sera.Totally 167 Salmonella isolates were identified from 1 045 samples and the isolation positive was 15.98%.And the positive detection rate of samples in different stages of production were listed bellowing:egg shell surface before disinfection,1.50%(3/200);egg shell surface after disinfection,0.50%(1/200);egg shell surface after piped,18.00%(36/200);dead embivos in the late incubation phage,24.00%(48/200);one day-old defective chickens,30.50%(61/200);PD-FT antibodies positive breeding hens,56.67%(17/30),significant higher than the PD-FT antibodies negative breeding hens(6.67%,1/15)(P<0.05).The surveillance detections showed that there were Salmonella contaminations of various degrees in all stages in the breeding companies from the hatchery to the breeder flock,especially through the vertical transmission route.Among the four companies,company DGGX17 whose breeding flocks were not carried out the eradication program was the most contaminated by 44.26%(27/61)of the total positive and its highest positive was found in the day-old defective chicks,and the positive rates in other stages in DGGX17 were also higher than those of the other three companies.And the highest detection rate for other three companies was from the PD-FT antibodies positive breeding hens.The serotype identification of 167 Salmon.ella isolates showed that there were totally 4 serotypes from 4 different serogroups:the absolutely dominant serotype was SP from group D(98.20%,164/167),followed by S.infantis,S.kentucky and S.koessen(all were 0.60%,1/167),from groups C1,C3 and A,respectively.The results of isolation and identification from the samples of different internal organs of the birds showed that the isolation rate of liver was the highest in day-old defective chicks(67.21%,41/61).17 out of the 30 PD-FT antibody-positive breeding hens were positive of Salmonella isolation and the ovary was the highest positive organ(52.94%,9/17),followed by the oviduct(47.06%,8/17),liver(47.06%,8/17)and spleen(41.18%,7/17),while those of the cloacal swabs were the lowest,either from that of the day-old defective chicks(21.31%,13/61)or the breeders 11.76%(2/17).K-B method recommended by WHO was used to detect the drug resistance of all the isolates against 16 common antibiotics.The results showed that 167 Salmonella isolates displayed resistance phenotypes against the 16 antimicrobials to certain degrees.The highest incidence of resistance in the isolates was against SIZ(100%),and then followed by NAL(97.60%,163/167),SXT(96.41%,161/167),AMC(86.83%,145/167).And the isolates were sensitive to NIT,CIP,CTX and CRO.Moreover,the proportion of the isolates with triple and more drug-resistant reached 100%,and 61.08%(102/167)of the isolates could resist 7 and more different antibiotics.And even three of isolates were found can resist up to 15 antibiotics tested.The results indicated the MDR phenomenon was quite popular.For the application of SYF,a challenge-protection experiment was performed.160 day-old Three-Yellow breeder chicks were divided iinto groups A,B,C(non-treated,challenged group)and D(non-treated,non-challenged group).All diets were based on a standard commercial diet without any antibiotics.Group A diet was supplemented with SYF product Safmannan and group B was supplemented with an organic acids product Acidipuire via drinking water,and groups C and D were fed the same diet without supplementation.All birds were ad lib accessed to the feed and drinking water during the experiment.At 7d,birds of group A,B,C were divided irnto 2 equal subgroups(A1 and A2,B1 and B2,C1 and C2).Subgroups A1,B1 and C1 were challenged with 2.83×108 CFU/bird of SP,while subgroups A2,B,and C2 were challenged with 2.0×109 CFU/bird of SG.Clinical signs and mortality were recorded daily.At 14,21,28,35 and 42 d,antibodies against SP and SG were detected by plate agglutinate test(PAT)with the SP-SG antigens.At 42 d,all birds were weighed and necropsied,lesions were recorded and challenged pathogens were isolated.Results showed that SP and SG isolation positive rates of groups A1,A2 were significantly lower(P<0.05)than those of groups B1,B2 and C1,C2,respectively(P<0.05).The average body weight(BW)of groups A1,A2 were significantly higher(P<0.05)than those of group B;,B2 and C,,C2,respectively(P<0.05).In field trial,day-old chicks of the commercial Three-Yellow chicken breeders were randomly divided into 3 groups.Group 1(2 833 birds)was fed a diet supplemented with Safmannan,group 2(2 489 birds)was fed the same diet and supplemented with Acidipure via drinking water,and group 3(3 513 birds)was fed the same diet and without any supplement as the control group.Antibodies in the sera of the birds against SP-SG were detected by PAT at 120 d.Antibodies positive rate of group 1 was significantly lower(P<0.05)than those of groups 2 and 3,while no significant difference(P>0.05)was found between groups 2 and 3.The results of the study demonstrated that there were various degrees of Salmonella contamination at different stages of the production in the chicken breeding companies in Guangxi,especially through the vertical transmission route and Salmonella pullurom was the most prevalent and dominant serotype.And the situation of drug resistance and multi-drug resistance of the Salmonella isolates was serious.SYF supplemented in the feed could significantly decrease the infection rates of Salmonella pulluronm and Salmoinella galli,narum,improve the body-weight gain of the challenged birds,and decrease the condemnation of the breeder due to the pullorum disease-fowl typhoid antibody positive.And it was more effective than the organic acids. |
PDF Full Text Request