| The duck industry is an important economic force in China.Since the start of this century,plastic flat net-rearing system(NRS)or the litter rearing system(LRS)with a simple barn was the primary intensive system for meat duck production,while pond-rearing litter system(PRLS)was widely used to raise laying ducks.Because these traditional rearing systems(LRS,NRS and PRLS)lack manure treatment facilities cause severe pollution to the waters and soil nearby,high incidence of disease in ducks,frequent use of antimicrobials,which seriously affect food quality and safety.The research and application of meat duck deep litter rearing system(DLRS)and laying duck cage rearing system(CRS)are of great significance to finding a way to solve the pollution and poor food quality associated with large scale waterfowl breeding.Thus,there is an urgent need to conduct research on effects of new rearing systems on production performance,food quality of ducks,and antimicrobial resistance.This research can not only contribute to improving management and biological safety for new duck rearing systems,but also can establish a risk-assessment method for the evolution of bacterial antimicrobial-resistance in the complex environment.This study contained the following four parts:1 Effects of deep litter system on the performance of meat ducks and laying ducks and environmental economics analysisThis experiment was conducted to investigate the effect of deep litter rearing system(DLRS)on the production performance of Cherry Valley ducks in different seasons(spring,summer,autumn and winter)and with different stocking densities(2.7,3.6,4.4 ducks/m2),whereas another group was the pond-rearing litter system(PRLS).Meanwhile,production performance,egg and meat quality were compared between Suyou No.l Laying Ducks in the DLRS and those in the PRLS.The results showed that,compared with the PRLS meat ducks,the average survival rate of the DLRS meat ducks in different seasons was 97.04%and its weight of slaughter was 2.76 kg,which were significantly increased by 1.29%or 1.85%(P<0.05)respectively.Meanwhile,the feed conversion was 2.18,which was significantly decreased by 2.24%(P<0.05).Survival rate,final weight and feed intake of meat ducks were the worst in summer and best in autumn.DLRS also significantly increased the ducks' survival rate and feed conversion with different stocking densities,and the duck production performance was improved when the stocking density decreased.Compared to PRLS laying ducks,DLRS ducks were 12 days younger for 5%laying rate(106 days of age)(P<0.01)and 10 days yonger for 50%laying rate(133 days of age)(P<0.05)in the winter.In DLRS group,the average egg weight was increased significantly than that of PRLS group(P<0.05).Compared to PRLS,laying ducks in DLRS had lower L*(lightness)value of leg muscle(P<0.05),higher a*(redness)value of leg muscle(P<0.05),higher shear force of breast muscle(P<0.05),lower drip loss and cooking loss of breast muscle(P<0.05),and had higher lower drip loss of leg muscle(P<0.05).These results indicate that in different seasons and different stocking densities,DLRS can improve the survival rate and feed conversion of meat ducks.The meat duck's performance is higher at lower stocking density;DLRS had no negative effects on production performance,egg quality and salt egg yolk quality in Suyou No.1 Laying Ducks.DLRS can improve the economic benefits and reduce the environmental pressure of manure and wastewater emission in large-scale breeding of ducks.2 Accumulation of antimicrobials and heavy metals in meat duck deep litter and their role in the persistence of antimicrobial-resistance Escherichia coli in different flocks on one duck farmMeat duck deep litter is considered to be an ideal environment for the evolution of bacterial antimicrobial resistance if it is under poor management.The aim of this study was to characterize the accumulation of antimicrobials and heavy metals in the deep litter and their role in the persistence of antimicrobial resistance of Escherichia coli,and evaluate the service life of the deep litter.Samples were collected from initial,middle and final stages of deep litter within three barns(0,4 and 8 round of meat duck fattening),nine flocks,with known consumption of antimicrobials in the controlled trail.The feed and litter levels of consumed antimicrobials and heavy metals were measured.E.coli(n=147)was isolated and identified by Eric-PCR(Enterobacterial repetitive intergenic consensus sequence PCR)and phylogenetic grouping technique,while Minimum inhibitory concentrations of antimicrobials and heavy metals were measured.This study confirmed the continuous accumulation of doxycycline and many heavy metals in the deep litter.The population of certain bacteria resistant to doxycycline(16 mg/L,100 mg/L)or ofloxacin(8 g/mL,50 g/mL)increased in the used deep litter(round 4 and 8).E.coli isolated from the three stages of sampling were highly resistant to ampicillin,tetracycline and doxycycline.Increased resistance to ceftiofur,enrofloxacin,ofloxacin and gentamicin was seen in the isolates from the final stage of deep litter.In addition,the percentage of isolates tolerant to zinc,copper and cadmium and the numbers of Group-B2 isolates all increased in the used deep litter,and the isolates of each stage belonged predominantly to commensal groups.The antimicrobial resistance of isolates with identical Eric-PCR patterns had improved from round 4 to 8,and the differences still existed in the resistance profiles of isolates with identical Eric-PCR patterns from different barns of the same round.It is concluded that deep litter is suitable for the evolution of bacterial antimicrobial resistance if continuous usage or accumulation of antimicrobials and heavy metals is not properly managed.3 Antimicrobial resistance and phylogenetic grouping of Escherichia coli isolates in different duck-rearing systemsNew types of duck-rearing management systems may give rise to antimicrobial resistance in bacteria and novel genotypes.The aim of this study was to ascertain differences between deep litter rearing system(DLRS),cage-rearing system(CRS),and traditional pond-rearing litter system(PRLS).The numbers of total bacteria and enterobacteriaceae cultured from each experimental rearing system were measured,and Escherichia coli was isolated and typed by phylogenetic group and ERIC-PCR techniques from 2013 to 2015.In addition,the minimum inhibitory concentrations of eight antimicrobials were determined.The levels of total bacteria and enterobacteriaceae in the CRS and litter of the PRLS(PRLS-L)samples were all higher than those in the DLRS and ponds of the PRLS(PRLS-P)samples.In total,116,38,59,and 29 E.coli were isolated from the DLRS,CRS,PRLS-L and PRLS-P,respectively.DLRS isolates showed the highest resistance to all the tested antimicrobials.Phylogroup A was the most common in each rearing system and showed the highest resistance to florfenicol,enrofloxacin,and ofloxacin.Among the rearing systems,the prevalence of phylogroup B2(12.9%)was highest in the DLRS.Some CRS and PRLS isolates were clustered,with identical ERIC-PCR genotypes and belonged to phylogroup A.In addition,all the phylogroup B2 isolates(19)exhibited resistance to tetracycline,and 8 of 15 phylogroup B2 DLRS isolates showed resistance to enrofloxacin or ofloxacin,which was not observed in the other isolates.The E.coli DLRS community appeared to be more antimicrobial resistant and pathogenic than the CRS and PRLS communities.4 Detection and analysis of PMQR determinants in quinolone-resistant Escherichia coli isolates in different duck-rearing systemsThe aim of this study was to investgate the prevalence and characterteristics of plasmid-mediated quinolone resistance(PMQR)determinats in quinolone-resistant E.coli from deep litter rearing system(DLRS),cage rearing system(CRS),and traditional pond rearing litter system(PRLS).The fluoroquinolones-resistant E.coli isolates from DLRS(87),CRS(10)and PRLS(14)was typed by phylogenetic grouping technique,while PMQR(qnrA,qnrB,qnrC,qnrD,qnrS,aac(6')-Ib-cr,qepA and oqxAB)and minimum inhibitory concentrations of 6 antimicrobilas were determined.All fluoroquinolones-resistant E.coli isolates from three duck rearing systems showed very high resistance to ampicillin,tetracycline and florfenicol(80-100%);oqxAB,qnrS and aac(6')lb were the most common in DLRS isolates,while qnrS and aac(6')lb were main PMQR determints for PRLS isolates,and only qnrS was detected for CRS isolates.42.5%DLRS isolates and 28.6%PRLS isolates were found to harbor at least one PMQR gene,whereas none of CRS isolates were detected.Among the phylogroup in this experiment,most PMQR determints(6)and multiple-gene profile(7)were found in phylogroup A isolates.Moreover,isolates carring qnr showed lower resistence level to Enrofloxacin than those without qnr.This study concluded that E.coli community in DLRS appeared to be more fluoroquinolones resistance,and types of PMQR gene and multiple-gene profile than CRS and PRLS. |
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