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1.
Campylobacter spp. in conventional broiler flocks in Northern Ireland: epidemiology and risk factors
McDowell SW Menzies FD McBride SH Oza AN McKenna JP Gordon AW Neill SD 《Preventive veterinary medicine》2008,84(3-4):261-276
Risk factors for Campylobacter infection in conventional broiler flocks in the time period up to the first removal of birds to slaughter were investigated over a maximum of five consecutive production cycles in a cohort of 88 broiler farms in Northern Ireland. Samples for Campylobacter culture, which consisted of 14 cloacal swabs per flock, were collected from one house on each farm prior to the first depopulation of birds. In total 388 flocks were sampled, of which 163 tested positive for Campylobacter spp. (42.0%; 95% CI 35.1–48.9%).
Data on farm and flock variables were obtained from questionnaires and random-effects logistic regression modelling used to investigate the association between these and the Campylobacter status of flocks. Six variables, all of which were significant at p < 0.05, were included in the final multivariable model. These included a combined variable on the presence of rodents on farms, which showed an increased odds of infection in flocks where the farmer reported having observed rodents during the production cycle (OR = 2.1) and/or where rodent droppings were observed at the sampling visit (OR = 2.9). Other variables that were significantly associated with an increased odds of infection included the age of the birds at sampling (odds ratio for its linear effect = 1.16 for each day of increase in age), season (summer versus other seasons OR = 2.0), farms with three or more broiler houses (OR = 2.9 compared to those with one house), the frequency of footbath disinfectant changes (OR = 2.5 for once weekly and OR = 4.0 for less than once weekly compared to twice weekly changes) and a categorical variable on the standard of tidiness and cleanliness of the broiler house ante-room (OR = 2.0 and OR = 4.9 for flocks from houses with poorer standards). There was no significant evidence of direct carry-over of infection from one production cycle to the next, neither was there evidence of other farm species acting as a source of infection. 相似文献
2.
Campylobacter, a foodborne pathogen closely associated with poultry, is considered to be an important agent of human gastroenteritis in New Zealand. The pathways involved in the contamination of poultry flocks remain unclear; however, many vectors, such as insects, rodents, and wild birds, have been implicated. Infestation of poultry houses by insects, particularly darkling beetles (Alphitobius diaperinus), is difficult to control. Furthermore, darkling beetles are known vectors for a variety of pathogens that include Salmonella, infectious bursal disease virus, Aspergillus, Escherichia coli, and Marek's disease virus. In this investigation, the relationship between darkling beetles and Campylobacter contamination of poultry flocks was investigated. A New Zealand breeder flock and four of its progeny broiler flocks were included in the study. Samples of beetles and of intestinal excreta of the birds were cultured for the presence of Campylobacter spp. A subset of the recovered isolates was subsequently genotyped using flaA short variable region (SVR) DNA sequence analysis. A large number of Campylobacter subtypes were isolated, indicating that Campylobacter colonization of poultry is likely to arise from a number of different reservoirs. However, a set of genetically distinct isolates were found to be common to the broiler flocks and to the beetles. This research provides data that indicates that Alphitobius diaperinus may serve as a source of Campylobacter contamination of poultry. A more thorough understanding of the relationship between beetle infestation and the Campylobacter status of poultry flocks should enable progress in further development of biosecurity control measures. 相似文献
3.
The carry-over of Campylobacter strains from one flock to a subsequent flock in the same broiler house has been studied using molecular epidemiological techniques. In all, 524 Campylobacter strains, isolated from two sequential broiler flocks from 60 broiler houses, were typed by restriction fragment polymorphism of the polymerase chain reaction (PCR) product of the flaA and flaB genes (fla typing). Selected strains were also typed using pulsed field gel electrophoresis (PFGE). By fla typing, 15 (21%) of the 60 houses with Campylobacter-positive sequential flocks had identical genotypes. In 10 (16% overall) of these houses the strains were also identical by PFGE. The difference in PFGE patterns in the strains from the three remaining houses may be indicative of genetic instability. Overall, these results suggest that carry-over from one flock to a subsequent flock in the same house is a relatively infrequent event and, therefore, that routine broiler house cleansing and/or disinfection is largely adequate to eliminate Campylobacter contamination. An alternative explanation of the low level carry-over is a persistent source or reservoir, external to the environment of the broiler houses. 相似文献
4.
Campylobacter jejuni is frequently present in the intestinal tract of commercial broiler chickens, and their drinking water has been proposed to be an initial source of bacteria for newly hatched chicks. We studied three sequential commercial broiler flocks raised in a house from which we had cultured C. jejuni from the nipple waters prior to placement of the first flock. Campylobacter cells were detected by immunofluorescence in the biofilm of the drinking nipples during the weeks when the flock was colonized with C. jejuni but not during weeks when the birds were negative. Campylobacter jejuni was isolated from the drinking water during the growth of the first flock and was present in the birds from all three flocks. Randomly amplified polymorphic DNA (RAPD)-polymerase chain reaction (PCR) typing with primer OPA11 indicated that seven distinct strains were present within the broiler house. One strain found in drinking water was similar to a strain found in birds in the second flock; however, RAPD-PCR with primer HLW85 showed that the strains were not identical. These results suggest that although the watering system is a potential source of C. jejuni in broiler flocks, the waterborne strain in this study was not detected in the birds. 相似文献
5.
One hundred flocks associated with five integrated poultry companies were monitored for one production cycle to investigate risk factors for campylobacter infection of poultry broiler flocks. Bacteriological samples were collected from one house of birds on each site at weekly intervals from 3 to 4 weeks of age until the birds were infected with campylobacter or the flock was depopulated (whichever was sooner). Environmental samples were obtained from 20 houses after cleansing and disinfection of the site before chick arrival. Conventional methods were used for the isolation of campylobacter. Questionnaires were used to collect information on potential risk factors for campylobacter infection. Discrete-time survival analysis was used to assess the influence of various exposures on the age at which the flock was infected with campylobacter.More than 40% of flocks were infected with campylobacter by the time the chicks were 4 weeks old and >90% by 7 weeks. Infection spread rapidly to most birds in a flock. Infection was not predictable by campylobacter status of the last flock reared on the site. (However, because most flocks were infected, the power to detect such an association was poor.) There was no evidence of environmental survival of campylobacters in broiler houses after adequate cleansing and disinfection. The most important predictors of protection from campylobacter were related to effective hygiene barriers (such as housing birds in buildings in a good state of repair, appropriate usage of disinfectant boot dips and a high standard of cleansing and disinfection of the drinking-water equipment). There was no evidence that rodents were a source of infection (but most sites operated effective vermin-control programmes). 相似文献
6.
P?ivikki Perko-M?kel? Pauliina Isohanni Marianne Katzav Marianne Lund Marja-Liisa H?nninen Ulrike Lyhs 《Acta veterinaria Scandinavica》2009,51(1):18
Background
Campylobacter is the most common cause of bacterial enteritis worldwide. Handling and eating of contaminated poultry meat has considered as one of the risk factors for human campylobacteriosis.Campylobacter contamination can occur at all stages of a poultry production cycle. The objective of this study was to determine the occurrence of Campylobacter during a complete turkey production cycle which lasts for 1,5 years of time. For detection of Campylobacter, a conventional culture method was compared with a PCR method. Campylobacter isolates from different types of samples have been identified to the species level by a multiplex PCR assay.Methods
Samples (N = 456) were regularly collected from one turkey parent flock, the hatchery, six different commercial turkey farms and from 11 different stages at the slaughterhouse. For the detection of Campylobacter, a conventional culture and a PCR method were used. Campylobacter isolates (n = 143) were identified to species level by a multiplex PCR assay.Results
No Campylobacter were detected in either the samples from the turkey parent flock or from hatchery samples using the culture method. PCR detected Campylobacter DNA in five faecal samples and one fluff and eggshell sample. Six flocks out of 12 commercial turkey flocks where found negative at the farm level but only two were negative at the slaughterhouse.Conclusion
During the brooding period Campylobacter might have contact with the birds without spreading of the contamination within the flock. Contamination of working surfaces and equipment during slaughter of a Campylobacter positive turkey flock can persist and lead to possible contamination of negative flocks even after the end of the day''s cleaning and desinfection. Reduction of contamination at farm by a high level of biosecurity control and hygiene may be one of the most efficient ways to reduce the amount of contaminated poultry meat in Finland. Due to the low numbers of Campylobacter in the Finnish turkey production chain, enrichment PCR seems to be the optimal detection method here. 相似文献7.
From August 1995 until December 1997, the effect of adding Salmonella enteritidis (SE) vaccination to a certified standardized biosecurity program in a situation of increased infection risk was examined in a field trial in The Netherlands. In this field trial, two groups of broiler-breeder flocks with increased infection risk were vaccinated, one group with VAC-T/TALOVAC logSE(group A) and the second group with SALENVAC (group B). The determination of increased infection risk in groups A and B was based on an SE infection history; flocks were either previously infected and treated (PIT) or had other risk factors than previously infected and treated (OPIT). SE infections in both vaccinated groups were assessed by monitoring according to the Dutch salmonella control program. Under field conditions, designation of a vaccinated and a control group on the farm was not possible. In the same period as the vaccinated groups, 608 nonvaccinated flocks (group C) were hatched and monitored according to the Dutch salmonella control program. The flock level occurrence of SE infection in the vaccinated groups was compared with the flock level occurrence of SE infection in the nonvaccinated group on the basis of comparability of infection risk. In group C, whether or not flocks had infection risk PIT was known and for risk factor OPIT, only whether or not a flock had been placed on a previously contaminated farm (= risk of reinfection) was known. The proportion of SE-infected flocks with risk factor PIT in the vaccinated groups was not significantly different from that in the nonvaccinated group C. Only the proportion of SE-infected flocks with a risk of reinfection in the vaccinated group B (0) was significantly lower (P = 0.02) than in the nonvaccinated group C (18%). The fact that no significant result was found in favor of group A is because of the small number of flocks in this part of the study. On the basis of the conditions of the setup of this trial, it can only be concluded that there is an indication that vaccination contributes in the reduction of SE reinfection in broiler breeder flocks. 相似文献
8.
V. V. Volkova R. W. Wills S. A. Hubbard D. L. Magee J. A. Byrd R. H. Bailey 《Zoonoses and public health》2011,58(3):158-168
In this study, we investigated risk factors associated with the probability to detect Salmonella in samples of litter collected within 2 h prior to new flock placement in 76 grow‐out houses on 38 conventional broiler farms located in the US states of Mississippi, Alabama and Texas. We evaluated characteristics of location and layout of the farm; area adjacent to and surrounding the house; house construction; condition and type of equipment in the house; litter management and other production, sanitation, visitation and biosecurity practices; non‐broiler animal species on the farm; and weather conditions on the 3 days leading up to flock placement. Logistic regression was used to model the relationships between probability to detect Salmonella in litter and potential risk factors. In the screening process, each risk factor was evaluated as a single fixed effects factor in a multilevel model that accounted for variability among the sampled farms and their production complexes and companies. Of almost 370 risk factors screened, 24 were associated with the probability to detect Salmonella in litter. These were characteristics of the surroundings of the house, house construction and conditions, litter management, length of downtimes between flocks in the house, biosecurity and farm location. After investigation of collinearity between these variables and building of models for important risk factor categories, the list of candidate variables for the final model was refined to eight factors. The final model demonstrated that a higher probability of detecting Salmonella in litter was strongly associated with the use of wood to construct the base of the walls or to cover the inside of the broiler house foundation, and with the use of fresh wood shavings to top‐dress or completely replace the litter between flocks. 相似文献
9.
Our objectives were to identify risk factors for contamination of French broiler flocks by Campylobacter. We used 75 broiler farms in western France. A questionnaire was administered to the farmers and samples of fresh droppings were taken to assess the Campylobacter status of the broiler flocks. 42.7% of the flocks were positive for Campylobacter spp. The risk of contamination of the broiler flocks by Campylobacter was increased in summer/autumn, in houses with static air distribution, when two or more people took care of the flock, in poultry farms with three or more houses and when the drinking water for the chickens was acidified. The presence of litter-beetles in the change room also increased the risk of contamination. The administration of an antibiotic treatment following a disease decreased the risk of a flock being contaminated by Campylobacter. 相似文献
10.
Connolly Dj Dwyer P Fagan J Hayes M Ryan E Costello E Kilroy A More S 《Irish veterinary journal》2008,61(8):533-537
Tuberculosis (TB), due to infection with Mycobacterium bovis was diagnosed in a flock of alpaca in Ireland in 2004. An epidemiological investigation was conducted to identify the risk of TB for farmed alpaca where TB is endemic, the origin of the infection, the potential for alpaca-to-alpaca transmission and appropriate control measures. The investigation focused on the alpaca flock (including the farm, animal movements and breeding, feeding and flock health practice), the disease episode (including animal disease events and subsequent control measures) and TB infection risk in the locality. The TB risk to alpaca is high in areas where infection is endemic in cattle and badgers and where biosecurity is inadequate. It is most likely that the source of infection for the alpaca was a local strain of M. bovis, present in cattle in this area since at least 2001. Genotyping of isolates identified a single variable number tandem repeat (VNTR) profile in both cattle and alpaca in this region. Although a tuberculous badger was also removed from the vicinity, bacterial isolation was not attempted. On this farm, infection in alpaca was probably derived from a common source. Alpaca-to-alpaca transmission seems unlikely. Two broad control strategies were implemented, aimed at the rapid removal of infected (and potentially infectious) animals and the implementation of measures to limit transmission. Tests that proved useful in detecting potentially-infected animals included measurement of the albumin-to-globulin ratio and regular body condition scoring. Skin testing was time consuming and unproductive, and early detection of infected animals remains a challenge. The flock was managed as a series of separate groupings, based on perceived infection risk. No further TB cases have been detected. 相似文献
11.
Generally, colonization with Campylobacter jejuni is first detected in broilers 2-3 wk after hatching. Once introduced into a flock, this infection spreads very rapidly. The sources and routes of transmission of C. jejuni in broilers remain debatable. In this study, the spread of infection was monitored in a commercial multipen broiler house in which birds were contained in discrete groups and sampled sequentially. Colonization was monitored in two broiler flocks up to slaughter. Serotyping and fla typing methods were applied to differentiate all the C. jejuni strains isolated. In flock 1, colonization was first detected at 32 days of age in birds located at the rear of the house. By 40 days, nearly all the birds were infected with the same strain (fla type 1.9). However, at 46 days of age, a second strain (fla type 3.7) was detected in some of the birds. These birds were also located toward the rear of the house. In flock 2, infection was detected at 5 wk of age. This infection was once again first detected in birds located at the rear of the house. In this flock, only a single fla type (1.1) was isolated throughout. A survey of the broiler house relative to the location of first point of infection indicated the use of an entrance door unprotected by boot dips. However, securing this door during the second flock study did not prevent infection. 相似文献
12.
Sasaki Y Tsujiyama Y Tanaka H Yoshida S Goshima T Oshima K Katayama S Yamada Y 《Zoonoses and public health》2011,58(5):350-356
The present study was conducted to estimate the prevalence of and to identify the risk factors for Campylobacter colonization in broiler flocks in Japan. Campylobacter colonization status in flock was evaluated by culturing pooled caecal excrement from 124 broiler flocks. Potential exposure to risk factors was evaluated with a questionnaire for the broiler producers. Odds ratios (ORs) were calculated using a multivariable logistic regression analysis. The prevalence of Campylobacter-positive flocks was 43.5% (upper and lower limits of 95% confidence interval (CI(95%) ): 34.8, 52.3). Multivariable logistic regression model identified two variables as risk factors for Campylobacter colonization. The ORs of Campylobacter colonization were higher in flocks in western Japan (OR=2.68; CI(95%) : 1.04, 6.91) than in eastern Japan, and in flocks supplied with undisinfected drinking water (OR=7.41; CI(95%) : 3.11, 17.66) than in those supplied with disinfected drinking water. These findings indicate that water may play an important role in Campylobacter colonization in broiler flocks in Japan and the use of disinfected water may reduce the risk of Campylobacter colonization. 相似文献
13.
The aim of this cross-sectional survey was to identify risk factors for Campylobacter spp. colonization in French free-range broiler flocks at the end of the indoor rearing period (between 35 and 42 days old). Seventy-three broiler farms were studied from March 2003 to March 2004 in France. A questionnaire was administered to the farmers and samples of fresh droppings were taken to assess the flocks'Campylobacter status by bacteriology. Campylobacter species were determined by PCR. A logistic regression analysis was used to assess the influence of various factors on flocks'Campylobacter status. 71.2% of the sampled flocks excreted Campylobacter spp. before going out on the range. The risk of a flock being colonized with Campylobacter was increased in the spring/summer period (RR=1.8, p=0.02) and autumn (RR=2.2, p=0.02) compared to winter, on total freedom rearing farms (RR=3.3, p=0.04) in comparison with farms with a fenced run, when the first disinfection of the poultry-house was performed by the farmer (RR=2.4, p=0.04) instead of a hygiene specialist, when rodent control was carried out by a contractor (RR=1.8, p<0.01) and not by the farmer and when the farmer came into the house twice a day as opposed to three time a day or more (RR=1.5, p=0.02). Use of a specific gate for chick placement decreased the risk of a flock being colonized with Campylobacter (RR=0.5, p=0.01) in comparison with using the gate for manual disposure or the door of the change room. 相似文献
14.
A surveillance study for thermophilic Campylobacter spp. in broiler flocks was carried out for the year 1998 in Denmark. The study included examinations of 4286 broiler flocks comprising samples from 57,000 birds. Overall, a flock prevalence of 46.0% was recorded. The species distribution was Campylobacter jejuni 86%, Campylobacter coli 11%, Campylobacter lari 1%, other not further diagnosed species 2%. The prevalence was significantly higher in the period from June to October (3.2 < odds ratio [OR] <1.8, P < 0.0002) and was significantly associated with abattoir (OR < 2.8, P < 0.0001) and the length of the period the broiler houses were left empty between flocks (download period; 6 days or more) (OR = 1.6, P < 0.0198). No association between Campylobacter colonization and the age at slaughter was found. Separating the flocks into batches for slaughter elevated the flock prevalence from 0.41 after the first batch had been slaughtered to 0.46 after all batches had been slaughtered. 相似文献
15.
Guerin MT Martin SW Reiersen J Berke O McEwen SA Fridriksdóttir V Bisaillon JR Lowman R;Campy-on-Ice Consortium 《Preventive veterinary medicine》2008,86(1-2):14-29
Our objective was to identify temperature-related risk factors associated with the colonization of broiler-chicken flocks with Campylobacter spp. in Iceland, with an underlying assumption that at minimum ambient temperatures, flies (Musca domestica) play a role in the epidemiology and seasonality of Campylobacter. At slaughter, pooled caecal samples were obtained from 792 flocks that hatched between March 15 and September 15 each year from 2001 to 2004, and cultured for Campylobacter. Daily temperature data (average, maximum and minimum temperatures) were obtained from the Icelandic Meteorological Office. We determined the closest weather station to each farm using ArcGIS 9. We then used logistic-regression models (with a random-effects term for farm) to examine associations between flock positivity and temperature-related predictors. The overall prevalence of Campylobacter was 27.4%, and the month with the highest prevalence (54.4%) was August. The final model included cumulative degree-days (CDD) above an average temperature of 4.4 degrees C and the presence of 1 or more days below a maximum temperature of 8.9 degrees C (threshold below which fly activity was expected to be substantially reduced and egg laying was not expected to occur) during the period 2-4 weeks (i.e. days 8-28) before slaughter. Below 79 CDD, the risk of flock Campylobacter colonization was generally low. Between 79 and 139 CDD, the risk increased gradually, but was lower for flocks raised during periods with 1 or more days <8.9 degrees C than flocks raised without days <8.9 degrees C. The risk increased sharply under conditions of high CDD (>139) and when the maximum temperature remained >8.9 degrees C during the period 2-4 weeks before slaughter. 相似文献
16.
ystein Angen Marianne N. Skov Mariann Chril Jens F. Agger Magne Bisgaard 《Preventive veterinary medicine》1996,26(3-4):223-237
A retrospective longitudinal study was conducted to identify risk factors associated with Salmonella enterica infection in Danish broiler production. The study was based on information in the antemortem database (AM database) where data were available for all broiler flocks slaughtered over the 2-year period from 1992 to 1993 in Denmark. The AM database contains information collected by the ante-mortem veterinarians, from the slaughterhouses, and from the salmonella examinations carried out at the National Veterinary Laboratory. The epidemiological unit was the individual broiler flock. The salmonella status of the flock was determined by examining the caecal tonsils from 16 3-week-old chickens from each flock. This procedure would detect a salmonella-infected flock, with a probability above 95%, if the prevalence is above 20%. Furthermore, the structure and quality of the collected data have been evaluated.
Fourteen variables were selected for analysis by multivariable logistic regression. An increased risk of salmonella infection in the broiler flocks was associated with the biggest hatcheries and feedmill, with an increasing number of houses on the farm, if the preceding flock was infected, and if the flock was reared in the autumn. Additionally, the main variables of the model were analysed by including a random effect at the house level. This resulted only in minor changes of the parameter estimates. 相似文献
17.
Our objective was to identify the risk factors for Campylobacter infection in Senegalese broiler flocks. Seventy broiler farms were studied around Dakar from January 2000 to December 2001 around Dakar. A questionnaire was administered to the farmers, and samples of fresh droppings were taken to assess the flocks' Campylobacter status. About 63% of the flocks were infected by Campylobacter spp.; Campylobacter jejuni was the most-prevalent species (P < 0.05). An elevated risk of Campylobacter infection was associated with other animals (mainly laying hens, cattle and sheep) being bred in the farm, the farm staff not wearing their work clothing exclusively in the poultry houses, uncemented poultry-house floors and the use of cartons that transport chicks from the hatchery to the farm as feed plates (rather than specifically designed feed plates). Alternatively, thorough cleaning and disinfection of poultry-house surroundings and manure disposal outside the farm were associated with decreased flock risk. 相似文献
18.
The litter of six turkey hen flocks was sampled using the drag-swab technique to determine the effectiveness of this method in detecting Salmonella arizona. Two flocks with the lowest biosecurity standards were found to have S. arizona. Results showed that the drag-swab technique can provide a sensitive and cost-effective measure of S. arizona infection within a flock. 相似文献
19.
Skov MN Spencer AG Hald B Petersen L Nauerby B Carstensen B Madsen M 《Avian diseases》2004,48(1):9-18
We evaluated the role of beetles infesting broiler chicken rearing facilities as potential reservoirs for Salmonella enterica infections between successive broiler flocks. In addition, their role as potential reservoirs for thermophilic Campylobacter spp. was also investigated. Fourteen broiler houses located at 11 different farms were included in the study. The houses were nonrandomly selected on the basis of their salmonella status; nine were persistently contaminated with salmonella whereas five were salmonella negative. For each broiler house, two consecutive broiler flocks (i.e., 28 broiler flocks in all) as well as beetles collected during both rotations of production and in the empty period (after cleaning and disinfection) between these flocks were monitored for the presence of salmonella. Examinations for the presence of campylobacter in the same sample materials were also performed. Beetles sampled during production were positive for salmonella or campylobacter or both. Furthermore, in one house, the occurrence of Salmonella indiana in two consecutive broiler flocks coincided with the presence of S. indiana-contaminated beetles in the empty period between the flocks. The genotype of the identified S. indiana was in all cases identical when analyzed by pulsed-field gel electrophoresis. However, our results also suggest that salmonella from beetles may not always be transmitted to the chickens and that beetles living in contaminated houses can remain free of infection. All cases of campylobacter-positive beetle samples were detected in connection with a positive chicken flock; in no case was campylobacter isolated from beetles taken from the empty period between rotations. Four beetle species were identified during this study. Alphitobius diaperinus was found in all houses and was relatively abundant in most. Typhaea stercorea and Ahasverus advena were found in eight and nine houses, respectively, and were abundant in most of these. Carcinops pumilio was found in small numbers in eight houses. No other insect species was identified. These investigations have shown that beetles in broiler houses infrequently are positive for salmonella. However, transmission of S. indiana between two consecutive broiler flocks can coincide with the presence of salmonella-contaminated beetles in the empty period, indicating that the beetles were the reservoir of S. indiana between the two flocks. Concerning campylobacter, the results suggest that beetles do not play a significant role as a reservoir of campylobacter from one rotation to the next. 相似文献
20.
1. Because thermophilic Campylobacter spp. are common in chicken flocks reared extensively, cross-sectional and longitudinal studies were carried out on organic and free-range farms to determine the onset of colonisation (lag phase) and likely sources of flock infection. 2. For 14 organic and 14 free range flocks, there was a difference in lag phases, with the former being colonized at a mean of 14·1 d in comparison with 31·6 d for the latter. Whereas most free-range flocks became colonized when released on to pasture, those reared organically were usually colonized at the housed brooding stage. 3. Further study of organic flocks on three farms over 7 successive crop cycles confirmed that colonisation was strongly influenced by the prevailing husbandry conditions and was not a consequence of the length of the rearing period. 4. Molecular epidemiological investigations on a farm showing the shortest lag phase, using PFGE typing with two different restriction enzymes (SmaI and KpnI) and flaA SVR sequence typing, revealed that potential sources of colonisation for organic chickens were already present on the farm at the time of chick placement. Such sources included the ante area of the brooding house, surrounding pasture and other livestock being kept on the farm. 5. Overall, the study demonstrated that, under UK conditions, the prevalence of colonisation was greater in extensive flocks (95-100%) than it was for conventional broilers (55%), similar to the situation in other countries, but all three management systems showed comparable levels of caecal carriage in positive birds (log(10)/g 6·2-6·7). 相似文献