Herd prevalence of Salmonella spp. in Danish pig herds after implementation of the Danish Salmonella Control Program with reference to a pre-implementation study

The problems addressed are: (1) comparison of prevalences of Salmonella spp. in different herd types in the Danish pig population after implementation of the Danish Salmonella Control Program (DSCP), and (2) to make a reference to a study from 1993/1994 (pre-implementation) with a discussion of possible biases when diagnostic methods differ slightly. The objectives were to present the prevalences of Salmonella spp., Salmonella Typhimurium, and multiresistant S. Typhimurium DT104 in Danish pig herds in 1998. Further, to discuss how herd prevalences may be compared to a previous study.A bacteriological study in 1998 comprised: (a) a random sample of slaughter pig producing herds (N=1962); (b) a random sample of farrow-to-grower (sow) herds (N=305); and (c) all breeding and multiplying (genetic) herds (N=366). A previous bacteriological study on Salmonella presence in 1993/1994 served as a model for the present study. The results of the study were that multiresistant S. Typhimurium DT104 was detected in one herd producing slaughter pigs. The herd apparent prevalences (HAPs) of Salmonella spp. were 11.7, 16.7 and 11.4% in genetic, sow, and slaughter pig herds, respectively. The conclusion of the study was that prevalence of multiresistant S. Typhimurium DT104 was low in the examined slaughter pig herds. The herd true prevalence (HTP) of Salmonella spp. in pigs had declined from before the start of the DSCP in 1993/1994 to 4 years later (1998).     

Salmonella serotypes present on a sample of Irish pig farms

A survey of the prevalence of Salmonella species infection was conducted on 59 Irish farrow-to-finish pig herds. Faecal samples were collected from the pens of first-stage weaners (growing pigs approximately three to 10 weeks of age), second-stage weaners (approximately 10 to 17 weeks of age) and fatteners, and from the dry sow and farrowing sow houses. The prevalence of infection was estimated to within 5 per cent with a 95 per cent confidence interval. Thirty of the 59 herds were infected, 12 with Salmonella Typhimurium only, eight with Salmonella Derby only and seven with both S Typhimurium and S Derby; serotypes London, Livingstone and Infantis were each isolated from a single herd. Farms in Ireland are assigned to one of three infection categories on the basis of the antibody levels in samples of meat juice taken at slaughter. When a herd was classified as either positive or negative on the basis of the isolation of Salmonella from at least one faecal sample there was no association between the herd's category as determined by meat juice serology and the probability of the isolation of Salmonella from the faecal samples. However, there were differences in prevalence between pigs at different stages of production in herds of different categories. Farrowing sow houses in moderately infected (category 2) herds had significantly lower infection rates (P < or = 0.05) than other herd categories and other stages of production. Pigs from first-stage weaner pens in slightly infected (category 1) herds were more likely to be infected with Salmonella than pigs at any other stage of production or category of herd.     

The correlation between Salmonella serology and isolation of Salmonella in Danish pigs at slaughter

In Denmark, a serological Salmonella surveillance programme in finishing pig herds has been in place since 1995. The programme was founded on data from experimental studies, which demonstrated a strong association between Salmonella serology and the prevalence of these bacteria. The current study was carried out in three Danish abattoirs to evaluate the correlation under field conditions. A total of 160 Danish finishing pig herds were included. Seven out of these were examined twice, yielding a total of 167 observations. The herds were selected according to their herd serology based on data from the national surveillance. From each herd, samples were taken from 10 finishers at slaughter. The prevalence of Salmonella bacteria was measured at four sites: (1) caecal-content; (2) carcass surface; (3) pharynx; and (4) caecal lymph nodes. A logistic regression model was constructed for each sampling site. Abattoir, sanitary slaughter and herd seroprevalence were used as explanatory variables. The results demonstrated that there was a strong association between herd serology and the prevalence of Salmonella bacteria measured at three of the sampling sites: caecal-content, pharynx, and carcass surface. For these sites, the odds for being culture-positive for Salmonella varied from 1.3 to 1.5 for each increase of 10% in herd serology (P < 0.0001). For caecal lymph nodes, however, no linear association was found.     

Demonstrating freedom from disease using multiple complex data sources 2: case study--classical swine fever in Denmark

A method for quantitative evaluation of surveillance for disease freedom has been presented in the accompanying paper (Martin et al., 2007). This paper presents an application of the methods, using as an example surveillance for classical swine fever (CSF) in Denmark in 2005. A scenario tree model is presented for the abattoir-based serology component of the Danish CSF surveillance system, in which blood samples are collected in an ad hoc abattoir sampling process, from adult pigs originating in breeding herds in Denmark. The model incorporates effects of targeting (differential risk of seropositivity) associated with age and location (county), and disease clustering within herds. A surveillance time period of one month was used in the analysis. Records for the year 2005 were analysed, representing 25,332 samples from 3528 herds; all were negative for CSF-specific antibodies. Design prevalences of 0.1-1% of herds and 5% of animals within an infected herd were used. The estimated mean surveillance system component (SSC) sensitivities (probability that the SSC would give a positive outcome given the animals processed and that the country is infected at the design prevalences) per month were 0.18, 0.63 and 0.86, for among-herd design prevalences of 0.001, 0.005 and 0.01. The probabilities that the population was free from CSF at each of these design prevalences, after a year of accumulated negative surveillance data, were 0.91, 1.00 and 1.00. Targeting adults and herds from South Jutland was estimated to give approximately 1.9, 1.6 and 1.4 times the surveillance sensitivity of a proportionally representative sampling program for these three among-herd design prevalences.     

Epidemiological investigations into the sources of Salmonella contamination of pork

This study was conducted to elucidate which phases of the pork production chain contribute to the Salmonella contamination on pork after slaughter. During 7 sampling days, samples were collected of randomly selected slaughter pigs and of pigs from selected Salmonella-infected and Salmonella-free herds, trucks, lairages, and slaughterlines, in two slaughterhouses. Salmonella genotypes, present on pork after slaughter, were compared with Salmonella types, present on the farm, in the truck, in the lairage, on slaughter equipment, and in pigs from other herds. Results showed that the slaughterline was the most important source of Salmonella contamination of carcasses. The farm was the most important source of contamination of livers, tongues, rectal samples and mesenterial lymphnodes, for pigs originating from sero-positive herds. The lairage was the most important contamination source for pigs originating from sero-negative herds, for all samples, except carcasses. It is recommended to avoid each direct or indirect contact between different herds along the whole pork production chain, especially between Salmonella-infected and Salmonella-free herds.     

Salmonella Dublin infection in young dairy calves: transmission parameters estimated from field data and an SIR-model

In this study we used field data collected from October 2001 to January 2002 to estimate number of days of faecal excretion of Salmonella Dublin bacteria and time to seroconversion in infected calves below the age of 180 days. Based on these estimates all calves in four endemically infected dairy herds were grouped into the following infection states: susceptible (S), infectious (I) and resistant/recovered (R). Resistant calves had either acquired maternal antibodies through colostrum or they have recovered from previous infection and had a high level of antibodies directed against Salmonella Dublin possibly protecting them from becoming infected again until the level of antibodies had decreased to sufficiently low levels. Using the antibody measurements and faecal excretion periods, it was possible to assign the most likely infection state to each calf per week of the study period. Estimates of transmission parameter, beta, were obtained from a generalised linear model relating the number of new infections to the proportion of susceptible and infectious calves per week. From beta, the reproduction ratio R at steady state and the basic reproduction ratio R(0) were estimated for each herd and across herds. The R(0) denotes the average number of new infections caused by one infectious individual that is introduced to a fully susceptible population. The point estimates for R(0) ranged from 1.1 to 2.7 in the study herds. However, the confidence intervals were wide. Data were too limited to show possible significant differences in the parameters between the study herds. However, the tendency in the data suggested that there may be important differences. Across herds the R(0) was close to two suggesting that on average one infectious calf will produce two new infectious calves when introduced into a fully susceptible population under typical Danish dairy production systems. Further, the analyses indicated that environmental contamination from infectious calves plays an important role in transmitting Salmonella Dublin between calves.     

Persistent fecal Salmonella shedding in five dairy herds

OBJECTIVE: To monitor patterns of Salmonella fecal shedding in naturally infected dairy herds, determine the association between fecal shedding and individual animal production measures, and evaluate potential risk factors for shedding of Salmonella organisms among cattle in dairy herds. DESIGN: Longitudinal study. SAMPLE POPULATION: 5 Ohio dairy herds. PROCEDURE: For 3 herds, fecal samples were collected from all mature cows and unweaned calves 7 times during an 18-month period. For the remaining 2 herds, fecal samples were collected from 50 lactating cows 6 times during a 12-month period. Individual animal production records for 3 herds were used to examine associations between individual fecal Salmonella shedding status and 305-day mature-equivalent milk production, somatic cell count, milk fat content, and milk protein content. Multivariable logistic regression was used to test for associations between fecal shedding status and breed, lactation status, lactation number, and duration of lactation. RESULTS: None of the adult animals had clinical signs of salmonellosis, but prevalence of fecal Salmonella shedding at individual collection times ranged from 0 to 99% for cows and from 0 to 67% for unweaned calves. Mature cows were more likely to be shedding Salmonella organisms than were unweaned calves. Within herds, lactation status and duration of lactation for individual animals were associated with Salmonella shedding status. Salmonella fecal shedding status was not associated with individual cow production measures. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that subclinical fecal Salmonella shedding can persist in dairy herds for up to 18 months with no measurable effects on health or production of individual cows.     

Bayesian modeling of animal- and herd-level prevalences

We reviewed Bayesian approaches for animal-level and herd-level prevalence estimation based on cross-sectional sampling designs and demonstrated fitting of these models using the WinBUGS software. We considered estimation of infection prevalence based on use of a single diagnostic test applied to a single herd with binomial and hypergeometric sampling. We then considered multiple herds under binomial sampling with the primary goal of estimating the prevalence distribution and the proportion of infected herds. A new model is presented that can be used to estimate the herd-level prevalence in a region, including the posterior probability that all herds are non-infected. Using this model, inferences for the distribution of prevalences, mean prevalence in the region, and predicted prevalence of herds in the region (including the predicted probability of zero prevalence) are also available. In the models presented, both animal- and herd-level prevalences are modeled as mixture distributions to allow for zero infection prevalences. (If mixture models for the prevalences were not used, prevalence estimates might be artificially inflated, especially in herds and regions with low or zero prevalence.) Finally, we considered estimation of animal-level prevalence based on pooled samples.     

Cilia-Associated Respiratory (CAR) bacillus infection in veal calves and adult cattle

Cilia-Associated Respiratory (CAR) bacillus is a filamentous bacterium that colonizes the ciliated epithelium of the respiratory tract of many animal species and that has been associated with chronic inflammatory lesions in naturally and experimentally infected rats, mice and rabbits. In the present study, the prevalence of CAR bacillus infection and histological lesions of the trachea in veal calf and adult cattle were investigated. Forty five healthy veal calves and 45 adult cattle, raised in 18 different herds were selected at slaughter. From each animal, a tracheal sample was processed for histology, stain-ed with the Warthin-Starry method to evaluate the presence of CAR bacillus, and with haematoxylin and eosin to evaluate the presence of inflammatory lesions. CAR bacillus was identified in 17 veal calves (37.7%) and in 7 adult cattle (15.5%). Inflammatory lesions were found in 42 veal calves (93.3%) and in 41 adult cattle (91.1%). Statistical analysis pointed out a significant correlation between the presence and number of CAR bacilli and the presence and number of lymphoid follicles (P = 0.0071) and the presence and severity of neutrophilic infiltrates (P = 0.0428). These results indicate that CAR bacillus infection is common in cattle and is correlated with tracheal inflammatory lesions.     

Effect of separate transport, lairage, and slaughter on occurrence of Salmonella typhimurium on slaughter carcasses

The study aimed to reduce cross-contamination between finishers from Salmonella-positive and Salmonella-negative herds during transport, lairage, and slaughter, thereby reducing the prevalence of Salmonella Typhimurium on slaughter carcasses. In Phase 1 of the study, pigs from Salmonella-negative herds were kept in lairage for 2-4 hours either in clean pens (intervention group) or pens contaminated with Salmonella-infected faeces (control group). All pigs were slaughtered on the same slaughterline, and carcass swabs 24 hours after slaughter revealed a low degree of cross-contamination in the pens: there was no difference in Salmonella-positive carcasses between intervention (1.7%) and control groups (0.8%). In Phase 2, control pigs from Salmonella-negative herds were mixed with pigs from Salmonella-positive herds during lairage for 2-4 hours, while the intervention group still consisted of pigs from Salmonella-negative herds. All pigs were slaughtered on the same line: first intervention, then control. Carcass swabs taken 24 hours after slaughter failed to show a reduction in Salmonella-positive carcasses in the intervention group (4.5%) compared with the originally Salmonella-negative pigs in the control group (3.6%). In pigs from Salmonella-positive herds the occurrence of Salmonella was substantially higher at 10.4%. When the results were corrected for 6 carcass samples found positive with S. Heidelberg on the same day, which was attributed to a transient hygiene failure, only 2.2% of the carcasses in the intervention group were Salmonella-positive. We conclude that even though cross-contamination occurs in the abattoir pens, its importance on the slaughter line may be greater. However, the final results of this study should be awaited to conclude whether separate slaughter of pigs from Salmonella-positive and Salmonella-negative herds should be recommended.     

Longitudinal study of hepatitis E virus infection in Spanish farrow-to-finish swine herds

Hepatitis E is a zoonotic disease and is highly prevalent in European swine livestock. There is a need to compare the infection dynamics of hepatitis E virus (HEV) between herds with the same production system and determine the percentage of animals that could arrive infected at slaughter age. Therefore, a longitudinal study was performed in six Spanish farrow-to-finish affected farms. Twenty piglets per farm were monitored from nursery to slaughter. RT-PCR and serology techniques were applied to analyze longitudinally collected sera and/or faecal samples. Liver and bile samples were also taken at the abattoir. Anti-HEV IgM were firstly detected at 7 weeks of age in 5 farms whereas at 13 weeks of age in 1 farm (farm 2). At slaughter age 50–100% of pigs had seroconverted to anti-HEV IgG in the former 5 farms whereas in the other herd only 5% of pigs were IgG seropositive (farm 2). Six out of 96 livers and 5 out of 80 biles analyzed were HEV positive at the abattoir (total percentage of infected animals: 11.5%). All these positive animals had already seroconverted except 2 pigs of farm 2. Hence, pigs can be seronegative at slaughter age being infected during the latest fattening period. Manipulation of HEV-infected livers or other organs from pigs could be considered a possible route of transmission in Spanish abattoirs. This study represents the first longitudinal survey on swine HEV infection dynamics conducted in different herds.     

Some aspects of the gastrointestinal microflora of veal calves fed different rations: a pilot study

The gastrointestinal microflora of veal calves reared on different diets was studied because the nature of this microflora affects the quality of veal as a result of contamination of carcass surfaces with intestinal contents during slaughter. Diet A consisted of a milk substitute, diet B of milk substitute + straw pellets and diet C of milk substitute + straw pellets + concentrates. In the rumen fluid of calves reared on diet A significantly higher counts of Gram-negative bacteria but lower counts of thermotrophic enterobacteriaceae were found than in calves reared on diets B or C. As for the faecal flora, diets B and C seem to result in significantly lower counts of Gram-negative bacteria and thermotrophic enterobacteriaceae. In 46% of the faecal specimens and 62% of the specimens of rumen fluid from calves fed on milk substitute only, Pseudomonas aeruginosa was isolated in mean counts of 4.1 log cfu/g and 5.2 log cfu/g respectively. P. aeruginosa could not be isolated from any specimen from calves receiving straw pellets. These results indicate that the inclusion of straw pellets in the diet of veal calves may increase the bacteriological safety and keeping quality of veal.     

Influence of age,sex and herd characteristics on the occurrence of Verocytotoxin-producing Escherichia coli O157 in Danish dairy farms

Verocytotoxin-producing Escherichia coli (VTEC) O157 is an important emerging human pathogen. Cattle are considered to be the main reservoir for VTEC O157. The objectives of this study were to determine the prevalence of VTEC O157 in Danish dairy herds and to investigate the relationship between shedding of VTEC O157 and a number of animal and herd characteristics. Sixty dairy farms were visited once in August-October, and from each herd faecal samples from up to 50 animals were analysed for VTEC O157 by enrichment, immunomagnetic separation (IMS), and plating on selective agar. In total, 2419 animals were sampled, and 3.6% of these excreted VTEC O157. These animals were located on 10 farms (17%). On average, 21% of the sampled animals in the positive herds excreted VTEC O157. Register data, including age, sex, breed, housing conditions and herd composition, were extracted from a database. No influence of herd size or housing conditions was found. A strong effect of age was seen with 2-6-month-old calves as the high-risk age group (8.6% positive) in contrast to calves <2 months (0.7%) and cows (2.4%). There was a non-significant tendency of bull calves to have a higher prevalence than heifers within the age group of 2-6 months. Significantly, more of the herds characterised by having relatively many bull calves or many animals bought into the herd were positive for VTEC O157. Despite the low incidence of human VTEC O157 infections in Denmark, the prevalence in Danish dairy herds was found to be at a similar level as in many other countries.     

Experiences from the Danish programme for eradication of bovine virus diarrhoea (BVD) 1994-1998 with special reference to legislation and causes of infection

The main experiences from the Danish bovine virus diarrhoea (BVD) eradication programme over 5 years from 1994 to 1999 are presented. The last 3 years of the programme has been strongly supported by legislation. The most important regulations have been blood testing of live animals before movement to other herds, common pastures or exhibitions, and monitoring of all herds at regular intervals for the presence of the infection. Nevertheless, free herds have experienced infection, e.g., 204 dairy herds in 1998. Of herds found to be infected in the period from July 1997 through June 1998 after previously having been registered to be BVD-free, 67 herds were thoroughly investigated. Nineteen herds (28%) were found infected because of purchase of pregnant cows or heifers which delivered persistently infected (PI) calves, and 24 (36%) and two (3%) because of PI animals on neighbouring pastures or in neighbouring farm houses, respectively. In five herds (7%) pregnant heifers had become infected on one and the same common pasture, while in 17 herds (25%) no immediate cause of infection could be demonstrated. Yet, airborne spread from PI herds as a source of infection was suspected in some of these cases. It was furthermore concluded from investigations presented, that antibody-positive AI bulls were a remote but unlikely possibility. Free-living deer in Denmark had to be considered uninfected. Presence of PI-animals in sheep on infected farms has been seen and is paid attention to in individual cases. The results underline the need for legislation to be used in eradication programmes in areas with a high prevalence of infection and to be introduced right from the beginning in order to minimise the risk of infection for free herds.     

The new classification system for slaughter-pig herds in the Danish Salmonella surveillance-and-control program

The Danish surveillance-and-control program for Salmonella in slaughter pigs was introduced in 1995. The key element of the program is a quick and correct identification of herds with high seroprevalence. After 5 years, the classification scheme was evaluated--and a revision was made. Data from two Salmonella screenings including a total of 1902 slaughter pig herds were used. For each herd, information was available on Salmonella status based on both microbiology and serology. Based on analyses of these data, suitable changes in the scheme were identified and their effect estimated by use of data from the Danish Salmonella Database including all herds in 2000. The classification scheme has been adjusted on the following points. (1) The sampling has been simplified into 60, 75, or 100 samples per herd per year depending on herd size. This means more-precise estimates for the seroprevalence among smaller herds. (2) Herds with an annual kill or=index 40, and the limit between Levels 2 and 3 to >or=index 70. If the Danish swine producers are interested, a Level 0 may be introduced (consisting of seronegative herds as an indication of a negligible Salmonella prevalence). The classification scheme was introduced in August 2001.     

Farm factors associated with the presence of Mycobacterium paratuberculosis infection in dairy herds on the New York State Paratuberculosis Control Program

An extensive questionnaire was developed and used to collect data from 33 herds that were on the New York State Paratuberculosis Control Program, to study farm factors associated with the presence of Mycobacterium paratuberculosis infection in dairy herds. The results of the last whole herd paratuberculosis fecal culture were used to indicate presence of infection in a herd, with herds having one or more animals positive classified as ‘infected’. The average prevalence within herds was 5.2%. Fourteen herds were uninfected and 19 herds had prevalences ranging from 0.7%–28.2%. Data on 31 continuous and 67 categorical risk factors were collected by questionnaire. Ten factors were significantly associated with prevalence risk of infection in the univariable logistic regression. These factors were: the type of farm operation (commercial/registered or both); earlier diagnosis of the disease before entering the control program; number of clinical cases in the previous year; whether clinical cases were raised or purchased animals; typical signs in clinical cases; exposure of calves 0–6 weeks of age to feces of adult cows; contact of young stock with adult animal feces from using the same equipment to clean the housing for both groups of animals; spreading feces on fields from which forage is later harvested and fed to animals of any age group; what is done with animals that are suspected of having paratuberculosis or test positive on culture; and frequency of cleaning the cow barn. Stepwise logistic regression was used to determine the significance of each risk factor while controlling simultaneously for the effect of other factors. The significant factors were the type of farm operation, clinical signs, and exposure of calves to feces of adult cows. Commercial herds, presence of clinical signs typical of paratuberculosis in animals, and exposure of calves 0–6 weeks old to feces of adult cows all indicate a higher likelihood that a herd is infected with M. paratuberculosis.     

Prevalence of helminth infections in swine in Denmark

During 1982-1984 the occurrence of helminths in 66 sow herds was determined by examining faecal samples from swine of different age groups. Ascaris suum was found in 88% of the herds, while Oesophagostomum spp. and Trichuris suis were found in 58 and 23% of the herds, respectively. Strongyloides ransomi and Hyostrongylus rubidus was not identified in any of the herds. The occurrence of both A. suum and Oesophagostomum spp. was strongly related to the age of the animals. A. suum was most frequently found in growing pigs (30% of the fatteners and 25% of the gilts), whereas only 11-19% of the animals of the adult stock were excreting eggs. In contrast the prevalence of Oesophagostomum spp. increased with the age of the hosts, from 10% of the fatteners to 35 and 44% of the sows and boars, respectively. T. suis occurred only very sporadically, with the highest prevalence being 3% in the gilts. In comparison to previous Danish surveys the present mean prevalences of A. suum and Oesophagostomum spp. were low. Extremely low herd prevalences were found among large herds with intensive management and housing. In these herds, the pigs were infected at a later stage in life than pigs in more traditionally managed herds.     

Recovery of Salmonella enterica from seropositive finishing pig herds

The aim of this study was to assess the probability of detecting Salmonella from pen faecal samples in seropositive classified finishing pig herds. The study involved 77 herds from Denmark (20), The Netherlands (20), Greece (17) and Germany (20). The serological herd status was determined by the blood-sampling of 50 finishing pigs. Bacteriological sampling was performed by 20 pen faecal samples per herd. Over-all, 47% of the blood samples had an OD% larger than 10 and 23% larger than 40. Salmonella was isolated from 135 (9.3%) pen faecal samples in 32 herds (42%). Twenty-eight of these herds (87.5%) had a within-herd seroprevalence larger than 50% at sample cut-off OD% > 10. In our study, there was an increasing probability of recovering Salmonella with increasing within-herd seroprevalence. However, this was only a moderate correlation. A correlation coefficient of 0.62 was found between the proportion of culture positive- and seropositive samples in a herd at cut-off OD%> 10 and of 0.58 at cut-off OD% > 40. Serology is a measure of historical exposure, which may or may not correlate closely to the microbiological burden at the time of sampling. Due to the low sensitivity of culture methods, apparent 'false-positive' serological results may well represent real infections not detected by bacteriological testing. For screening purposes, serological testing provides an indication of exposure to Salmonella, which forms the basis for targeted sampling, intervention and logistic slaughter procedures.     

Effects of fluorequinolone treatment acidified feed, and improved hygiene measures on the occurrence of Salmonella Typhimurium DT104 in an integrated pig breeding herd

Worldwide, the use of antimicrobials in food production has been associated with drug resistance in foodborne pathogens such as Salmonella. However, little is known about the efficaciousness of fluorequinolone treatment on Salmonella Typhimurium T104 infections in pig breeding herds. A combined eradication procedure with enrofloxacin application on sows and piglets, feeding of encapsulated organic acids to sows, disinfection with peracetic acid, separation of the growers from the sows and serological discrimination using a new whole-cell-based enzyme-linked immnosorbent assay (ELISA) was evaluated for the suitability to eradicate and to control endemic S. Typhimurium DT104 infections in a closed herd. Thirty-seven sows and their piglets were treated everyday from day 14 ante partum until the day of weaning. Eighteen sows and their piglets served as controls. From the first day of life until day 168 after birth, faecal samples (n = 1671) of all piglets were analysed for Salmonella shedding. In parallel, systemic antibody responses were monitored by whole-cell-based isotype-specific ELISA systems. From birth to weaning the prevalence in both groups was between 2% and 9%. After weaning, intermittent shedding could be observed in both groups, and salmonellae could be found in up to 7.7% of the faecal samples. As a result, a dramatic increase in Salmonella-infected growers was observed, as of day 115 after birth, 47.4% of the animals of the treated group were tested positive for S. Typhimurium. Our results indicate that despite long-term antibiosis treatment and optimized hygiene measures, shedding of S. Typhimurium by the sows and the subsequent infection of their offspring could not be effectively prevented. Although it could be not shown that elimination of S. Typhimurium DT104 infection was achieved, the disinfection procedures described and the diagnostic test used are effective instruments to decrease the Salmonella load and to identify individual infected animals. Both of these are important factors for an improved consumer protection.     

Effect of organic acids in drinking water during the last 2 weeks prior to slaughter on Salmonella shedding by slaughter pigs and contamination of carcasses

In this study, we investigated the effect of adding organic acids to the drinking water of finishing pigs 2 weeks prior to slaughter on the shedding and prevalence rate of Salmonella at slaughter. Approximately 600 animals from four Belgian pig herds infected with Salmonella were included. At two herds, the study was conducted twice. Before the start of the study, overshoes were taken at the different herds. Two weeks prior to the expected slaughter date, the pigs were randomly divided into two groups (treatment and control group) each containing on average 50 animals within each herd. The treatment group received from this day onwards acidified drinking water (pH = 3.6-4.0), the control group received non-treated water (pH = 7.8-8.5). All other housing, feeding and management factors were identical in both groups. At the slaughterhouse, 10 pigs of each group (20 pigs for each group of study group 6) were randomly selected and sampled (blood, contents of ileum and rectum, mesenteric lymph nodes and carcass swabs). All samples were immediately transported to the laboratory and submitted to Salmonella isolation. Salmonella was isolated out of 11.9% (66/554) of the samples taken at the slaughterhouse, with the highest frequency found in the content of the ileum (18.7%), followed by 17.8% in the lymph nodes, 7.2% in the content of the rectum and 3.6% in the carcass swabs. The results did not reveal a significant difference between the treatment and control groups for the different slaughterhouse samples. The study documented that the investigated control strategy namely, the strategic application of organic acids during the last 2 weeks prior to slaughter was insufficient to decrease Salmonella shedding and contamination shortly before and during slaughter.