M.J.M. Tielen

Herd level husbandry factors associated with the serological Salmonella prevalence in finishing pig herds in The Netherlands

A national program to reduce Salmonella in pork and pork products should include monitoring and intervention at farm level. To develop an adequate intervention strategy at farm level, risk factors for Salmonella infections in finishing pigs have to be determined. In this study, blood samples were collected randomly at two slaughterhouses from slaughter pigs. Samples were tested by the Dutch Salmonella ELISA, based on the O-antigens 1, 4, 5, 6, 7 and 12, using a cut-off of OD%=10. This ELISA has been calibrated against the Danish ELISA to give comparable results. Workers from herds from which at least forty blood samples had been collected, were asked to participate in a questionnaire. In total, 353 questionnaires were obtained and analysed. Significant risk factors associated with the proportion of seropositive samples were identified by multiple linear logistic regression. The feeding of a complete liquid feed containing fermented by-products and the omission of disinfection after pressure washing a compartment as part of an all-in/all-out procedure, were both associated with a lower Salmonella seroprevalence. A small to moderate herd size (<800 finishing pigs), a previous diagnosis of clinical Salmonella infection in the herd, the use of tylosin as an antimicrobial growth promoter in finishing feed, or herds which had more than 16% of the livers of their pigs condemned at the slaughterhouse as a result of white spots were associated with a higher Salmonella seroprevalence. Hypothetical intervention strategies based on these risk factors can be studied for their effect on the Salmonella seroprevalence and practical applicability in field studies.

Salmonella infections in finishing pigs in The Netherlands: bacteriological herd prevalence, serogroup and antibiotic resistance of isolates and risk factors for infection

Salmonellae are wide spread in man and animals world wide and are of increasing significance as causative agents of foodborne diseases in man. The European Union, national authorities and the pig industry are therefore more and more interested in the Salmonella status of the pig population. The aim of this study was to estimate the bacteriological prevalence of Salmonella in finishing pig herds, the serogroup and the resistance to antibiotics of the isolated Salmonellae and a preliminary risk analysis of factors associated with infection. For this, 317 finishing pig herds were randomly selected from a database containing 1500 herds in the southern part of the Netherlands. In each herd 24 samples of fresh faeces were collected from two compartments with pigs close to market weight. Per compartment 12 samples of faeces were pooled into one pooled sample. Pooled samples were cultured in duplicate. Salmonella spp. were recovered from 71 out of 306 herds (23%) in which two compartments could be sampled. A total of 108 isolated Salmonellas were serotyped: 71 serogroup B, 3 serogroup C1, 6 serogroup C2, 22 serogroup D1, and 6 isolates neither serogroup B, C or D1. Of a total of 115 Salmonella isolates tested, none were resistant to colistin, enrofloxacin, flumequin or gentamicin. Automated liquid feeding of by-products, and membership of an Integrated Quality Control (IQC) production group were associated with a decreased risk of infection, while use of trough feeding was associated with an increased risk of infection. It is necessary to test these presumed risk factors in intervention studies to evaluate their potency to reduce the Salmonella prevalence in finishing pigs and thereby reduce the risk of Salmonellosis in people consuming pork.

Lung function and chronic respiratory symptoms of pig farmers: focus on exposure to endotoxins and ammonia and use of disinfectants.

OBJECTIVES--The prevalence of chronic respiratory symptoms among pig farmers is known to be high, but the aetiology of these symptoms is not yet unravelled. Long term average exposure to dust was evaluated, endotoxins and ammonia and use of disinfectants were compared with chronic respiratory symptoms and depressed base line lung function. METHODS--A cross sectional study was performed among 194 Dutch pig farmers, of whom 100 had not and 94 had chronic respiratory symptoms. Exposure-response relations were evaluated with multiple logistic and linear regression analysis. Estimates of long term average exposure were based on two personal exposure measurements, taken on one day in summer and one day in winter. Information on use of disinfectants and disinfection procedures was assessed by a walk through survey and interview by telephone. RESULTS--Exposure to dust, endotoxins, and ammonia were not related to chronic respiratory symptoms. Duration of the disinfection procedure and pressure used at disinfection were strongly and positively related to chronic respiratory symptoms. A significant inverse association between base line lung function and endotoxin exposure was found only among asymptomatic farmers. Ammonia exposure and duration of the disinfection procedure were significantly associated with base line lung function in the entire population. CONCLUSION--Results suggest that use of disinfectants is an important aetiological factor in chronic respiratory health effects of pig farmers. This factor has not been studied before. Results also suggest an aetiological role for exposure to endotoxins and ammonia in development of chronic respiratory health effects, but longitudinal studies with detailed exposure assessment strategies are required to assess their roles.

INCIDENCE OF CLINICAL MASTITIS IN A RANDOM SAMPLE OF DAIRY HERDS IN THE SOUTHERN NETHERLANDS

The incidence of clinical mastitis and distribution of pathogens in dairy cows was estimated in 171 randomly selected dairy herds in the southern Netherlands. A total of 1103 quarter cases were reported. The average annual incidence rate was 12.7 quarter cases per 100 cows per year. The most frequent isolates from clinical cases were Escherichia coli (16.9 per cent), Staphylococcus aureus (14.4 per cent), Streptococcus uberis (11.9 per cent) and Streptococcus dysgalactiae (8-9 per cent). Most cases were reported in early lactation: 25.4 per cent in the first month of lactation for all cows, and 39.1 per cent in the first month for first lactation cows. The rear quarters had a significantly higher incidence rate than the front quarters. Cows with an E coli infection showed more general clinical signs than cows infected with S aureus, S uberis and S dysgalactiae. A significantly higher incidence was observed in herds with a low (<150,000 cells/ml) bulk milk somatic cell count than in herds with a count above 250,000 cells/ml.

Salmonella seroprevalence at the population and herd level in pigs in The Netherlands

The aim of this study was to provide baseline data on the population and herd Salmonella seroprevalence in sows and finishers. For the population estimates in 1996 and 1999 and the herd prevalences for sows and gilts, blood samples from swine vesicular disease (SVD) and pseudorabies monitoring programmes were used and tested in an indirect Salmonella enzyme-linked immunosorbent assay (ELISA). The herd prevalence for finishers was determined using blood samples collected at two slaughterhouses. The population prevalence for finishers in 1996 and 1999 was 23.7 and 24.5%, respectively, and for sows 40.5 and 60.4%, respectively. The prevalence in free range (FR) finishers was significantly higher (44.6%) than in intensively housed finishers in 1999, identifying a hazard group for possible extra pork and pork product contamination. Of 406 finishing herds, 9% were completely seronegative for Salmonella (cut-off OD%>10). Of these 406 finishing herds, 69.7% had Salmonella-status I (low prevalence), 21.7% status II (moderate prevalence) and 8.6% status III (high prevalence) (cut-off OD%>40). In 46 multiplying sow herds, 20 breeding sow herds and 20 matching replacement gilt herds, the average herd prevalences were 54, 44.4 and 19.3%, respectively. Two gilt herds were completely seronegative. The prevalence in the gilt herds was never higher than in the matching breeding sow herds. Agreement on methodology and calibration of ELISA tests would make these results comparable between countries and is a prerequisite for a co-ordinated and integrated program to reduce Salmonella in pork in the European Union.

Administration of acidified drinking water to finishing pigs in order to prevent Salmonella infections

Summary The aim of the study was to test whether acidified drinking water, with two millilitres of an acid mixture per litre, was able to reduce the number of Salmonella infections in finishing pig herds. In each compartment, half of the pens were supplied with acidified water and the other pens served as negative control. In three herds the required dose was not applied to the pigs as a result of various practical problems. In another herd, all pigs remained seronegative throughout the study. Analysis of the remaining three herds showed a large and significant treatment effect in one herd (P<0.001). As a result of the small number of observations and the overall lower seroprevalence in the control groups, the other two herds only showed a statistical trend to a treatment effect (0.10<P<0.05). The main practical problem was the clogging of drinking nipples as a result of fungal growth in the pipelines.

Epidemiological studies on lesions in finishing pigs in the Netherlands. I. Prevalence, seasonality and interrelationship

Abstract Data from meat inspection services at two large regional abattoirs in the Netherlands were used to study the prevalence and seasonal variation of pathological lesions in finishing pigs. A data recording system including 12 codes for lesions was used. From 1 February 1987 until 1 February 1989, approximately 550 000 finishing pigs originating from 205 pig herds were slaughtered and observed. The lesions atrophic rhinitis, arthritis, inflammation of the leg, inflammation of the tail, skin lesions, partially affected and condemned liver, and abscess (es) in the lungs occured at frequencies of less than 1%. Only some respiratory disorders occured at frequencies of 2–11%. For all of the lesions investigated there were significant prevalence differences between pig herds, but there were also significant differences in the prevalence between the two slaughterhouses for the lesions arthritis and inflammation of the tail in pigs. The highest prevalences of pneumonia and of the skin lesions were in January–February and the lowest in July–August. The highest prevalences of abscesses in the lungs and of condemned liver were in October–November and the lowest in April–May. The highest prevalence of pleurisy was in June–August and the lowest in December–January. The highest prevalence of arthritis was in August–October and the lowest in February–April. The interralationships between lesions at the herd level were quite limited for most of the lesions.

Sero‐epidemiological screening of pig sera collected at the slaughterhouse to detect herds infected with Aujeszky's disease virus, porcine influenza virus and Actinobacillus (Haemophilus) pleuropneumoniae in the framework of an Integrated Quality Control (IQC) system

Over a period of six months, approximately 4700 blood samples were collected from 97 pig-finishing farms in the provinces of Noord-Brabant and Gelderland and screened for antibodies with respect to Aujeszkys disease virus (ADV), porcine influenza virus (PI) and Actinobacillus (Haemophilus) pleuropneumoniae (App). There were significant differences in the percentages of seropositive pigs between the two provinces, which may be related to the difference in the density of the pig population in the two provinces. In practice, it was possible to perform a reliable sera collecting procedure at the slaughterhouse. No farms remained seronegative with respect to most of the disease agents during the sampling period. There was a high degree of variation in the percentages of seropositive pigs per farm as to most of the disease agents. Evidence was found that animals that were seropositive with respect to ADV were significantly more susceptible to becoming seropositive with respect to App. serotype 2, and vice versa. The same connection was observed for PI serotype H1N1 and PI serotype H3N2. Furthermore, evidence was found that pigs seropositive with respect to PI serotype H1Ni only, or to PI serotype H1N1 and ADV or PI serotype H3N2 show a significant decrease in average daily weight gain compared to pigs that were seronegative.

Longitudinal changes in lung function associated with aspects of swine confinement exposure.

Several aspects of swine-confinement farming appear to be leading to adverse respiratory effects. This study was set up in a longitudinal design to study the association between certain characteristics of farms or the way they are run and a decline in lung function. A cohort of 171 pig farmers was observed for 3 years. Lung function was measured. Exposure to farm characteristics was determined at the start of the observation period, using data from standardized farm surveys and from diaries kept by the participants. Mean decline in lung function was 73 mL/year for forced expiratory volume in 1 second (FEV1) and 55 mL/year for forced vital capacity (FVC). A longitudinal decline in FEV1 was significantly associated with the use of quaternary ammonium compounds as disinfectants (an additional 43 mL/year) and also with the use of an automated dry feeding system (an additional 28 mL/year). The association with the use of wood shavings as bedding material was not statistically significant. The impact of these characteristics in a longitudinal study provides stronger evidence for causal inference than that shown in previous cross-sectional designs. This may be useful in promoting preventive measures.

Intensive regional vaccination with a gI-deleted vaccine markedly reduces pseudorabies virus infections

The development of marker vaccines against pseudorabies virus (PRV) and companion diagnostic tests have enabled us to perform a unique field trial. In this study, the effect of intensive regional vaccination on pig-finishing herd immunity was directly measured by comparing the seroprevalence of antibodies to glycoprotein I in trial and control groups. The seroprevalence of infected finishing herds in the trial region decreased from 81% at the start of the trial to 19% after 2 years (p < 0.001). The mean seroprevalence of infected pigs in these herds diminished from 49 to 5% (p < 0.001). In the control group, representing routine PRV control, no significant change in seroprevalences was noticed.