Danish Broiler Research Articles

Resistance to quinolones in Campylobacter jejuni and Campylobacter coli from Danish broilers at farm level.

To investigate the prevalence of quinolone resistance among Campylobacter jejuni and Camp. coli isolates from Danish poultry at the farm level, as well as for the whole country. Data and isolates were collected from a national surveillance of Campylobacter in poultry. Quinolone resistance was investigated by determination of minimum inhibitory concentration (MIC) to nalidixic acid and enrofloxacin. Among Camp. jejuni and Camp. coli combined, 7.5% were resistant to nalidixic acid. Quinolone resistance varied considerably from farm to farm, with 0% on some farms and almost 100% on others, but the resistance was evenly distributed geographically. With respect to isolates from farms where resistance was detected, quinolone resistance was higher among Camp. coli (28.7%) than among Camp. jejuni (11.3%). PFGE typing of quinolone-resistant and quinolone-susceptible isolates from four farms indicated that certain resistant isolates belonged to specific clones that were able to persist on the farms during several rotations, even in the absence of selective pressure. Some clones were present and repeatedly isolated in both a quinolone-susceptible and quinolone-resistant variant. Overall, quinolone resistance among Campylobacter isolates from Danish broilers was 7.5% in 1998 and 1999; it was higher among Camp. coli than Camp. jejuni. Genetic diversity among resistant isolates was lower than among susceptible isolates, and certain clones existed in both a resistant and a susceptible variant. Some resistant clones appeared to persist on the farms and were repeatedly isolated from poultry flocks. The study is important for the understanding of persistence and dynamics of Campylobacter in broiler houses. It also highlights the extent, farm-to-farm variation and persistence of quinolone-resistant Campylobacter in broiler houses.

A questionnaire-based, retrospective field study of persistence of Salmonella Enteritidis and Salmonella Typhimurium in Danish broiler houses

A questionnaire-based, retrospective field study was conducted in 78 Danish broiler houses (analytical units) on 42 farms. In spring 1997, all these broiler houses had been infected with Salmonella Enteritidis, phage type 8, and/or Salmonella Typhimurium, definitive-type 66, by day-old chicks delivered from the same hatchery. Because these two salmonella types had not been detected in the Danish broiler sector before and the broiler houses were infected in a period of low salmonella prevalence, the study could focus on farm-related factors, without being distorted by other salmonella infections. The same person visited all 78 broiler houses, and farm-related factors were listed both from personal observations and by interrogating the person in charge of attending to the broilers. Additional factors (noted at the visits) were recorded in a later telephone interview. Altogether, 187 variables were analyzed. Broiler houses were divided into single-infection houses (which had one or both of the salmonella types in only one crop), and multiple-infection houses (where infection occurred in multiple crops). This was done both generally and separately for each of the salmonella types. Factors associated with house status—but that were beyond the control of the farmer—were the salmonella type and the percentage of salmonella positive samples in the first crop. Factors which could be controlled by the farmer and which were associated with reduced prevalence of multiple-infection houses included antiseptic soap and water for washing hands in the anteroom, hygiene barriers when removing dead broilers, gravel alongside the broiler house, systematic checks of indoor rodent-bait depots, and combined surface and pulse-fogging disinfection.

Relations between the occurrence of resistance to antimicrobial growth promoters among Enterococcus faecium isolated from broilers and broiler meat

From 1995 to 2001, Enterococcus faecium isolates were collected from broiler flocks at slaughter and broiler meat products at retail outlets and were tested for susceptibility to classes of antimicrobials used for growth promotion in broilers in Denmark, namely: evernimicin, glycopeptide, macrolide and streptogramin. By February 1998, all antimicrobial growth promoters (AGPs) were withdrawn from the Danish broiler production. The present study investigates, by logistic regression analyses, the (1) changes in the occurrence of AGP resistance among E. faecium from broilers and broiler meat from the fourth quarter of 1995 to the fourth quarter of 2001 and (2) relations between the occurrence of AGP resistance among E. faecium isolates from Danish broilers and AGP resistance among E. faecium isolates from the broiler meat of Danish and unknown origin collected in the same quarter within the year. In the present study, we showed that after the AGP withdrawal, a significant decline in resistance to avilamycin, erythromycin, vancomycin and virginiamycin was observed among E. faecium from broilers and broiler meat. In addition, a decline in the occurrence of AGP resistance among E. faecium from Danish broilers was associated with a decrease in the predicted probability of isolating an AGP-resistant E. faecium isolate from a randomly selected broiler meat product. In the analyses “relations between the occurrence of AGP resistance among E. faecium isolated from broilers and broiler meat collected in the same quarter” errors in the explanatory variable were expected. Therefore, a simulation study was performed to validate the results from logistic regression analyses. The results obtained by the two methods were similar.

Risk factors associated with the introduction of acute clinical infectious bursal disease among Danish broiler chickens in 1998

The objective of the present study was to investigate risk factors associated with the introduction of acute clinical infectious bursal disease (IBD) among Danish broiler chickens in 1998. Data on 218 flocks were collected from hatcheries, abattoirs, farmers and veterinarians; 49 of the flocks had experienced acute clinical IBD (cases), 169 were unexposed (controls). The study was carried out using a case-control design. Cases were defined as the first flock on each premises to experience acute clinical IBD, and these were compared with non-diseased, non-IBD-vaccinated control flocks chosen randomly from each unaffected farm. The resulting numbers of cases and controls used for statistical analyses were 16 and 61, respectively. Statistically significant associations were seen between the initial 16 Danish cases of acute clinical IBD in 1998 and certain hatcheries, age of parent birds and a certain feed mill.

Prevalence of cytolethal distending toxin (cdt) genes and CDT production in Campylobacter spp. isolated from Danish broilers.

The pathogenesis of campylobacter infection in man is largely unknown, although cytolethal distending toxin (CDT) has been incriminated as a virulence factor. However, little is known about the cdt genes in Campylobacter spp. isolated from broiler chickens. A total of 350 cloacal swabs was collected and tested by conventional culture and PCR. Of the 114 Campylobacter isolates obtained, 101 (88.6%) were identified as C. jejuni and 13 (11.4%) as C. coli by conventional methods. cdt genes were detected by PCR in all the isolates except one C. jejuni isolate. Cytotoxic effects were produced in a Vero cell line, by 100 of the C. jejuni isolates. In contrast, 10 C. coli isolates produced much lower levels of toxin and 3 produced no detectable toxin. These results confirm the common occurrence of campylobacter infection in chickens and indicate that cdt genes are commonly present in both C. jejuni and C. coli isolates from broilers, but that there are distinct differences in CDT production in these two closely related species.

DEVELOPMENT OF A PCR ASSAY SUITABLE FOR CAMPYLOBACTER SPP. MASS SCREENING PROGRAMS IN BROILER PRODUCTION

Campylobacter is the most common cause of human acute bacterial gastroenteritis worldwide. In order to comply with the demands of consumers for food free of bacterial pathogens, a mass screening program for Campylobacter in Danish broilers has been carried out based on conventional bacterial culture techniques since 1998. However, using conventional culture methods is time consuming and laborious, and therefore a Polymerase Chain Reaction (PCR) Campylobacter detection assay suitable for mass screening of cloacal swab samples from broilers was developed. By comparing the PCR detection with conventional culture methods, significantly more samples were found positive for Campylobacter with the PCR method. The PCR method is rapid, sensitive and suitable for mass screening for Campylobacter in poultry. Using this PCR method Campylobacter can be detected within 15 h. Notably, the method can be applied to detect Campylobacter directly from chicken feces at the species level.

Pre-harvest surveillance of Campylobacter and Salmonella in Danish broiler flocks: a 2-year study

In national surveillance programmes of broiler flocks carried out in Denmark during 1998 and 1999, 89,110 samples for Campylobacter representing 8911 broiler flocks were taken at 10 different abattoirs, and 44,550 samples for Salmonella were taken from the same flocks in the broiler houses at the farms. Of the swabs, 42.5% were Campylobacter positive. Most positive samples were found during July, August and September, while the lowest number of positive samples were found during January, February, March and April. Of the flocks, 5.5% were Salmonella positive, but no seasonal variation was observed. For each flock, the presence of Campylobacter and Salmonella was recorded in order to estimate the possible correlation between colonisation with the two pathogens. In conclusion, no significant effects on intensive cleaning and disinfection procedures on Campylobacter occurrence could be demonstrated, and no significant correlation between occurrence of Campylobacter and Salmonella infections in Danish broilers could be demonstrated which is in contrast to previous observations on concurrent colonisation of broilers with these two zoonotic pathogens.

The effect of discontinuing the use of antimicrobial growth promoters on the productivity in the Danish broiler production

On 15 February 1998, the Danish poultry industry voluntarily decided to discontinue the use of all antimicrobial growth promoters (AGPs). To investigate how the removal of AGPs influenced the broiler productivity in Denmark, data from 6815 flocks collected from November 1995 to July 1999 by the Danish Poultry Council were analysed. The three flock parameters were: kilogram broilers produced per square meter (per rotation), feed-conversion ratio (total kilogram feed used per rotation/total kilogram live weight per rotation) and total percent dead broilers ((number of dead broilers during the rotation/number of broilers put in the house per rotation) × 100). Data were analysed using a mixed model, allowing the correlation structures in the data to be taken into account. The analyses showed that kilogram broilers produced per square meter and percent dead broilers in total were not affected by the discontinued use of AGPs. However, the feed-conversion ratio increased marginally 0.016 kg/kg and has remained at this level throughout the rest of the study period.

Serologic Reactions against Salmonella in Samples from Broiler Parent Stock with and without Preceding Colibacillosis: A Case-Control Study

In the Danish Salmonella Control Program, eggs from broiler parent flocks are surveyed by serologic analysis every 4 wk for antibodies against Salmonella lipopolysaccharide O-antigens 1, 4, 5, 9, and 12 (Mix-enzyme-linked immunosorbent assay [ELISA]) and 6 and 7 (Infantis-ELISA). The antibody response is measured in percentage optical density (OD%) of a strong positive reaction, and the cutoff value has been determined to be 40 OD%. Two or more reactors above 40 OD% will place the parent flock under suspicion. There has been concern about possible cross-reactions between Salmonella spp. and other Enterobacteriaceae, e.g., Escherichia coli, because a high specificity of a Salmonella antibody test is desirable. Moreover, false-positive Salmonella results have economic consequences and impede planning the production. A case-control study based on cases of clinical E. coli infections (colibacillosis) from two Danish hatcheries, supplying about 62% of the Danish broiler production, is described. In order to eliminate a possible bias from age and season, the controls were matched on age of the birds and on time of submitting the samples. This study shows that flocks with preceding colibacillosis did not have higher salmonella reactions than matched flocks without a preceding colibacillosis. This observation was confirmed in longitudinal studies.

Thermophilic Campylobacter spp. in Danish broiler production: A cross-sectional survey and a retrospective analysis of risk factors for occurrence in broiler flocks

In order to elucidate the rate of thermophilic Campylobacter spp. carriage in Danish broiler production and to identify risk factors for occurrence of campylobacter in broiler flocks, a total of 88 randomly selected broiler flocks were tested for campylobacter infection, and a subsequent study of risk factors based on a questionnaire was conducted. The sample material comprised cloacal swabs from live birds before slaughter, and neck skin samples from carcasses at the end of the processing line. A total of 52% of the flocks were found Campylobacter spp.-positive before slaughter. At the end of processing, 24% of the flocks were positive. The species distribution was 87% Campylobacter jejuni, 8% Campylobacter coli and 5% Campylobacter lari. The following parameters were identified as significant risk factors: lack of a hygiene barrier (odds ratio (OR) = 3.1, 1.1 < OR < 9.3), presence of animals in the vicinity of the broiler house on farms with a missing hygiene barrier (OR = 7.0, 1.6 < OR < 33.9), livestock other than chickens on farms with a missing hygiene barrier (OR = 7.6, 1.4 < OR < 44.9), dividing the flock into batches for staggered slaughter (OR = 6.8, 1.2 < OR < 49.3), a down period of less than 14 days (OR = 5.0, 1.2 < OR < 22.6), and feeding purchased wheat rather than home-grown wheat (OR = 3.1, 1.0 <OR < 9.9). The presence of a hygiene barrier was found to be the single most important biosecurity measure for production of campylobacter-free broilers.

Risk factors associated with Salmonella enterica serovar typhimurium infection in Danish broiler flocks

A retrospective longitudinal study was conducted to identify risk factors associated with Salmonella enterica serovar typhimurium (S. typhimurium) infection in Danish broiler flocks. The data included all broiler flocks slaughtered in 1995, and the epidemiological unit was the individual broiler flock. The S. typhimurium status was determined by microbiological examination of 60 fresh fecal samples. This procedure should detect an infected flock with a probability above 95%, if the prevalence is above 5%, and given that the sensitivity of the test is 100%. Nineteen variables were selected for analysis. Five factors and an interaction term were found significant by multivariate logistic regression analysis. An increased risk for S. typhimurium infection was associated with two parent flocks, one confirmed infected and one suspected of being infected with S. typhimurium, with two of the hatcheries, and with five houses on the farm. An interaction between season and the previously mentioned hatcheries, and a random effect at farm level was also found to be statistically significant. Twelve variables were not found to be associated with S. typhimurium infection: medication, growth promoters, breed of the laying flock, animal density, size of the flock, area of the house, age of the house, geographical location of the farm, observation of beetles, number of days between disinfection and replacement, visual appearance of the bedding, and age of the chickens when they were tested for Salmonella. Three variables (feed mill, slaughterhouse, and Salmonella status of the preceding flock) were not evaluated in the multivariate analysis due to collinearity with other included variables.

Generalised linear mixed models analysis of risk factors for contamination of Danish broiler flocks with Salmonella typhimurium

We present a retrospective observational study of risk factors associated with the occurrence of Salmonella typhimurium (ST) in Danish broiler flocks. The study is based on recordings from 1994 in the ante-mortem database maintained by the Danish Poultry Council. The epidemiological units are the broiler flocks (about 4000 flocks) which are clustered within producers. Broiler flocks with ST-infected parent stocks show increased risk of salmonella infection, and also the hatchery affects the salmonella status significantly. Among the rearing factors, only the use of medicine as well as the time of rearing, and the sampling method are significant. Epidemiological control would seem most efficient on starting at the top levels of the production hierarchy from which a major part of the ST contamination is derived. A secondary purpose of the study is to evaluate different statistical approaches and software for the analysis of a moderately-sized data set of veterinary origin. We compare the results from five analyses of the generalised linear mixed model (GLMM) type. The first observation is that the results agree reasonably well and lead to similar conclusions. A closer look reveals certain patterns of bias and estimation accuracy that correspond well with theoretical findings and practical experience reported in the statistical literature.

Typhaea stercorea (Coleoptera: Mycetophagidae), a carrier of Salmonella enterica serovar Infantis in a Danish broiler house.

In December 1994, Salmonella enterica serovar Infantis (S. Infantis) was accidentally introduced into a Danish broiler house by stocking an S. Infantis-infected broiler flock of 39,900 day-old chicks. At the time of the study, the infection had persisted through 6 broiler cycles. Typhaea stercorea (L.), the hairy fungus beetle, was found in large quantities inside and around the broiler house. Various attempts to control the beetle had failed; T. stercorea had been uncontrollable on the farm since Alphitobius diaperinus (Panzer), the lesser mealworm, was eradicated approximately 10 yr earlier. We investigated the ability of T. stercorea to act as a carrier of S. Infantis in the broiler house between 2 broiler cycles. We examined the empty, cleaned, and disinfected broiler house for S. Infantis 3 d before stocking the 7th broiler flock, and S. Infantis was isolated from the beetles only. Of 20 singly examined T. stercorea, 9 (45%) were S. Infantis positive. A rapid spread of the infection was seen in the 7th broiler flock; 100% of the culled chicks were S. Infantis positive 3 d after stocking. Under experimental conditions chicks were observed eating beetles, and when 5 d-old, specified pathogen-free chicks were fed with S. Infantis-positive T. stercorea collected from the broiler house, all 5 chicks became infected in 4 d. We conclude that T. stercorea may act as a potential carrier of S. Infantis between successive broiler cycles.

Hatchery‐borne Salmonella enterica serovar Tennessee infections in broilers

Summary A substantial increase in the prevalence of 5. enterica serovar Tennessee was observed in broiler flocks in Denmark at the turn of the year 1994 and in the following months. Epidemiological data indicated that a single hatchery was involved in spreading of the infection. Molecular characterization of S. enterica serovar Tennessee isolates from Danish broilers (1992 to 1995), the suspected hatchery and strains from various other sources included for comparison was initiated in order to trace the source of infection of the broilers. In general, strains of S. enterica ser. Tennessee showed only minor genotypic variation. Three different ribotypes were demonstrated when EcoRI was used for digestion of DNA. Two types were obtained by the use of HindIII. Nine different plasmids and seven different plasmid profiles were demonstrated. A 180 kb plasmid was, however, only demonstrated in isolates from broilers and the hatchery. Sixty‐nine per cent of the broiler isolates obtained during the period 1992 to 1995 harboured this plasmid and 88% of the hatchery isolates contained a plasmid of the same size. An increased number of the broiler isolates (79%) contained this plasmid at the turn of 1994. Restriction enzyme analysis of the plasmid ensured that the plasmids from broilers and the hatchery were identical. By analysis of cleaning and disinfection procedures and by sampling of different control points in the hatchery it was shown that S. enterica ser. Tennessee had colonized areas of the hatchers which were protected from routine cleaning and disinfection. Subsequent inclusion of these areas into the sanitation programme resulted in the elimination of S. enterica ser. Tennessee from the hatchers, and a decreasing prevalence of S. enterica ser. Tennessee was observed in broiler flocks during the following months.

A retrospective study on salmonella infection in Danish broiler flocks

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.

Temporal Secretory Patterns of Growth Hormone in the Danish Broiler Lines Selected for High Body Weight or for Improved Food Efficiency

Abstract Plasma growth hormone (GH) secretory profiles of 8-week-old male and female broiler chickens selected for high body weight at 42 days of age (GL line) or for improved food efficiency between 18 and 39 days of age (FCR line) were compared. A pulsatile GH secretory pattern was still present for all the 8-week-old chickens examined. Overall mean GH levels, and to a lesser extent GH baseline and GH amplitude values, were higher for FCR chickens compared with GL chickens. Mean GH concentrations, baseline and amplitudes were slightly, but not significantly, superior in males. Length and frequency of pulses were not influenced by line or sex. In view of the current knowledge on age- and sex-related changes in pulsatile GH secretion, it is argued that the line and sex differences would have been more pronounced in younger chickens. Based on this, the hypothesis that the amplitude of the pulsatile GH release is related to protein conversion efficiency and protein deposition rather than to average body weight gain is corroborated.

Influence of subclinical virus infections and other factors on broiler flock performance

1. The influence of subclinical infections with infectious bursal disease virus, adenoviruses, REO viruses and chicken anaemia virus and of various production variables on broiler flock performance was investigated. 2. A significant effect could not be demonstrated of any of the viral infections either alone or in combination. 3. The production results were profoundly influenced by several other factors, that is, breed, diet, stock density and contents of whole wheat grain in the food. 4. The incidence of horizontally-transmitted subclinical chicken anaemia virus infection in Danish broilers has decreased significantly during the period 1988-89 to 1992-93, probably because of improved hygiene and management. The incidence of adeno- and REO virus infections did not change during the same period. 5. It is concluded that factors other than subclinical viral infections presently have an economic impact on performance observed in the Danish broiler production.

A voluntary Salmonella control programme for the broiler industry, implemented by the Danish Poultry Council

In the light of data and experience gained over the last two decades, initiatives made to combat and control Salmonella in the Danish broiler industry are described and the results obtained so far are discussed. The main elements include evaluation of the establishments, procedures and processes used, including bacteriological assessment, advice and guidance, routine bacteriological monitoring, and also research. Results obtained are used in the control of breeding stock, parent stock, hatcheries, broiler farms, slaughterhouses, feedmills and transport systems.

A Comparison of the Feeding Value for Broilers of Corn, Grain Sorghum, Barley, Wheat, and Oats, and the Influence of the Various Grains on the Composition and Taste of Broiler Meat

INTRODUCTIONTHE Danish broiler industry is dependent, in part, on the use of imported grains, mainly corn and grain sorghum. Baelum and Petersen (1964) reported the results of a broiler feeding trial using diets containing 40% corn, sorghum, wheat, barley, and oats—all the diets having the same ratio of metabolisable energy (ME) to digestible protein. The results of the trials showed that the chickens fed corn, sorghum, and barley diets, gained equally in weight, while the birds fed on the wheat and oat diets gained respectively 3% and 6% less. The chickens fed on the wheat, barley, and oats diets consumed respectively 3%, 4%, and 7% more feed per kg. gain, than the birds fed on the corn and sorghum diets. Some chickens from each group were tested for their meat quality, and it was reported by Jensen (1964) that grilled birds fed on the grain sorghum diet had…