Effect of feed withdrawal prior to slaughter on prevalence of gastric ulcers in pigs

OBJECTIVE: To determine whether withdrawing feed from pigs prior to slaughter had any effects on prevalence or severity of gastric ulcers. DESIGN: Split-plot design. ANIMALS: 873 pigs. PROCEDURES: At the finishing barn, pigs were assigned to 30 pens. Feed withdrawal times (0, 12, or 24 hours) were assigned to pens at random, and pigs in each pen were marketed in 3 groups over a period of 4 weeks. The first marketing group consisted of the 10 heaviest pigs in each pen, the second consisted of the next 10 heaviest, and the third consisted of all remaining pigs. Feed was withheld from all pigs in each pen prior to removal of each marketing group. Thus, feed was withheld once, twice, or 3 times for pigs in the first, second, and third marketing groups, respectively. RESULTS: Feed withdrawal time was not significantly associated with ulcer score at the time of slaughter. Ulcer scores and prevalence of chronic damage were higher in the third marketing group, regardless of feed withdrawal time. Prevalence of severe damage, prevalence of chronic damage, and prevalence of esophageal constriction increased as carcass weight decreased. No pigs died of gastric ulceration. CONCLUSION AND CLINICAL RELEVANCE: Results suggest that withdrawal of feed from pigs prior to slaughter does not increase damage to the stomach and that repeated feed withdrawal does not result in fatal gastric ulceration.     

Risk factors for gastric ulcers in Australian pigs at slaughter

The stomachs of pigs (n=15,741) originating from 136 herds from the Australian states of Queensland, Western Australia, Victoria and New South Wales were examined at slaughter for the presence of oesophago-gastric ulcers (OGUs). Stomachs were categorised as being normal, hyperkeratotic, eroded, ulcerated, or having strictures. A questionnaire was distributed to piggery owners to identify factors associated with an above-average herd prevalence of OGU. Thirty percent of all pigs examined had OGU (median within-herd prevalence of 17%). The median within-herd prevalence in Victoria (53%) was significantly higher than in Western Australia (30%) or Queensland (7%). The prevalence of OGU in culled breeding animals was significantly higher than in porkers or baconers from the same herds. There was no difference between the prevalence of OGU in male and female pigs sampled from the same Western Australian herds. The relationship between OGU and herd and pig risk factors was assessed by random effects logistic-regression analysis. Herds with a high prevalence of OGU were more likely to feed ad libitum (OR=13.7), use automated feeding systems (OR=7.8), feed a pelleted ration (OR=384) and get water from a dam rather than from a bore or river (OR=3.8). Furthermore, for every change in the ration formulation for finisher pigs, the risk of OGU increased 1.5 times.     

Validation of a method for the detection of virulent Yersinia enterocolitica and their distribution in slaughter pigs from conventional and alternative housing systems

Various methods have been described in the literature for the detection of virulent Yersinia enterocolitica in pigs. The risk factors for pig herd contamination have yet to be determined. The objective of this study was to validate a sensitive method for the detection of Y. enterocolitica and to describe the distribution of the bacteria in pigs at slaughter from conventional and alternative ("organic") housing systems. First, samples were collected from tonsils, caecum with caecal contents, and the caecal lymph nodes of 60 slaughter pigs. These samples were used to compare the sensitivity of six different laboratory culture methods either in common use or described in the literature with that of a polymerase chain reaction with two primer pairs (multiplex PCR). Then, only PCR was used to examine tonsils, caecum and caecal lymph nodes from two groups of slaughter pigs: 210 from six conventional fattening farms and 200 from three with alternative housing. The results of the multiplex PCR were positive in 28 cases. All culture methods proved inferior to PCR in sensitivity. In the second part of the study, PCR detected 36 (18%) positive pigs from alternative housing and 60 (29%) from conventional housing (p<0.05). The highest rate of Y. enterocolitica contamination was found in tonsils (11% alternative, 22% conventional; p<0.05), followed by caecum (5%, 11%) and lymph nodes (2%, 7%). The housing system appears to be one important factor in the prevalence of this common pathogen in pig herds, as we found important differences between the two systems studied here. In the conventional system, the main risk factors appeared to be sourcing pigs from different pig suppliers, use of commercial feed and transportation to slaughter.     

Prevalence and risk factors associated with adventitious bursitis in live growing and finishing pigs in south-west England

The prevalence and risk factors associated with adventitious bursitis in 912 growing and finishing pigs, originating from 20 different housing systems in south-west England, were investigated in this study. The overall prevalence of bursal lesions was 63.4%. Bursae were seen at different aspects of the hock: lateroplantar, plantar, medial and point of the hock. The most frequently affected site was lateroplantar (54.4%) followed by plantar (12.5%), medial (2.0%) and finally the point of the hock (0.7%). There was no difference in the proportions of left and right hocks affected. Bursal lesions were seen in pigs from 8 to 28 weeks of age and prevalence increased with age. Also, the longer the period pigs spent in the pen, the more likely they were to have bursitis. After accounting for the effect of herd of origin, bedding which covered the whole pen (OR 0.11) or only the lying area (OR 0.29) was the most important factor which reduced the risk of bursitis. A wet slurry film in the dunging area (OR 1.67) and a difference between the solid area and the concrete slats greater than 3 cm (OR 3.11) were significantly associated with an increased risk of bursal lesions.     

Non-infectious factors associated with macroscopic and microscopic lung lesions in slaughter pigs from farrow-to-finish herds

A cross-sectional epidemiological study was conducted in 150 randomly selected farrow-to-finish herds to investigate which non-infectious factors might act as risk indicators for the prevalence and severity of macroscopic and microscopic lung lesions in slaughter pigs. Data were collected during herd visits through inspections of the pigs and through interviews with the farmers. Macroscopic lung lesions of pneumonia and pleuritis were recorded at slaughter from 25 pigs per herd, and microscopic lung lesions of lymphohistiocytic infiltration were recorded from 10 pigs per herd. The median herd level prevalences were 24 per cent for pneumonia, 16 per cent for pleuritis and 60 per cent for lymphohistiocytic infiltration. Pneumonia lesions were negatively associated with pleuritis lesions and positively associated with lymphohistiocytic infiltration. Pleuritis lesions were negatively associated with lymphohistiocytic infiltration. The prevalence and the severity of pneumonia lesions were increased by a high frequency of purchasing gilts and by a slaughter date in January to February. The presence of a growing unit also increased the severity of pneumonia. The prevalence and the severity of pleuritis lesions were higher when there were more pig herds in the municipality, and when there were poor biosecurity measures, and their prevalence was increased by a slaughter date in January to February, and their severity by a slaughter date in March to April. An increase in the airspace stocking density in the finishing unit also increased the prevalence of pleuritis. The prevalence and the severity of lymphohistiocytic infiltration in the lung tissue were higher in herds purchasing gilts. Pigs raised in pens with slatted floors were also at higher risk of more severe lesions of lymphohistiocytic infiltration.     

Chronological study of Mycoplasma hyopneumoniae infection, seroconversion and associated lung lesions in vaccinated and non-vaccinated pigs

A field trial was conducted to study Mycoplasma hyopneumoniae (Mh) infection dynamics by nested polymerase chain reaction (nPCR) and serology in pigs of a farm affected by enzootic pneumonia (EP). Moreover, correlation of Mh detection at different respiratory tract sites with presence of EP gross and microscopic lung lesions was assessed. These parameters were studied and compared between vaccinated (two doses at 1 and 3 weeks of age versus one dose at 6 weeks of age) and non-vaccinated pigs. Animals were monitored from birth to slaughter by nPCR from nasal swabs and by serology. From 3 to 22 weeks of age, an average of three pigs per treatment and per batch were necropsied (n = 302). The remaining pigs were sent to the slaughter (n = 103). Nasal, bronchial and tonsillar swabs were taken from the necropsied/slaughtered pigs; gross and microscopic EP-suggestive lung lesions were also assessed. Single and double vaccination resulted in earlier seroconversion and higher percentage of Mh seropositive pigs compared to control group. At slaughter, double vaccinated pigs showed lower percentage of EP-compatible gross lung lesions and lower Mh prevalence at upper respiratory tract sites (nasal cavity and tonsil) than control pigs.     

African swine fever among slaughter pigs in Mubende district, Uganda

Owing to frequent reports of suspected outbreaks and the presence of reservoir hosts and vectors (warthogs, bushpigs and O. moubata ticks), African swine fever (ASF) is believed to be an endemic disease in Uganda. There have, however, been very few studies carried out to confirm its existence in Uganda. This study was carried out to describe the prevalence of ASF based on pathologic lesions and analysis of serum samples from slaughtered pigs during a suspected outbreak in the Mubende district of Uganda. The study was based on visits to 22 slaughterhouses where individual pigs were randomly selected for a detailed ante-mortem and post-mortem inspections. Sera were also collected for laboratory analysis. A total of 997 pigs (53.7% male and 46.3% female) were examined for lesions suggestive of ASF and sero-positivity of sera for ASF antibodies. The sera were tested using enzyme-linked immunosorbent assay (ELISA) and positive samples were further confirmed with an immunoblot assay. The results showed that 3.8% (38/997) of the pigs examined had clinical signs and post-mortem lesions suggestive of ASF. Two of 997 (0.2%) sera analysed were positive for ASF antibodies. Of the sub-counties investigated, Bagezza (12%) and Kiyuni (11%) had the highest prevalence of lesions suggestive of ASF based on ante- and post-mortem examination results, while Mubende town council (1.7%) had the lowest. This study found a low number of pigs (3.8%) with lesions suggestive of ASF at slaughter and an even lower number of pigs (0.2%) that were seropositive at slaughter, however a significantly higher number of pigs were slaughtered during the outbreak as a strategy for farmers to avoid losses associated with mortality.     

Slaughterline records of various postmortem pathological lesions and their influence on carcass and meat quality in slaughtered pigs

The aim of this study was to identify the prevalence of pathological lesions in pigs from small‐scale farms and to determine associations between pathological lesions and hematological parameters, and carcass and meat quality in slaughtered pigs. The study was conducted on 625 pigs (~115 kg) originating from 20 small‐scale farms. Any signs of pneumonia, pleurisy, pericarditis, and liver milk spots were recorded as present or absent. Complete blood count was investigated. The following carcass quality parameters were measured: live, hot and cold carcass weights, cooling loss, dressing percentage, backfat thickness, and meatiness. Meat pH and temperature were measured 45 min postmortem. Of the 625 examined pigs, 41.8% had pneumonia, 23.5% pleurisy, 2.7% pericarditis, and 29.9% liver milk spots. The presence of pathological lesions in slaughtered pigs adversely affected hematological parameters, reduced live, hot and cold carcass weights, and meatiness and had deleterious effects on meat quality (higher pH_45min and higher prevalence of dark, firm and dry meat). In conclusion, this study showed a high prevalence of pathological lesions in slaughtered pigs, indicating serious health problems in smallholder pig production systems. The presence of single and, especially, multiple pathological lesions in slaughtered pigs negatively affected hematological parameters, and carcass and meat quality.     

Varying effects of infections with Mycoplasma hyopneumoniae on the weight gain recorded in three different multisource fattening pig herds

Pigs in three specialized fattening herds were studied with respect to the effect of infection with Mycoplasma hyopneumoniae on weight gain. Individual pigs were weighed four times at 4-week intervals during the fattening period and their daily weight gain over the rearing period was calculated. A blood sample was collected on each weighing occasion and analysed for the presence of antibodies to M. hyopneumoniae. The lungs of the principals were inspected at slaughter and the extent of pneumonic lesions was registered by a specially developed technique that has been proven to warrant a high degree of repeatability. No serum antibodies to M. hyopneumoniae were detected in one of the herds, and no pneumonic lesions were recorded at slaughter in that herd. In the other two herds, the prevalence of pigs with serum antibodies to M. hyopneumoniae increased from 6 to 54% and from 31 to 81%, respectively, during the fattening period. The prevalence of pneumonic lesions at slaughter in these herds was higher the later the pigs seroconverted. On the other hand, the extension of the lung lesions tended to be higher among pigs that seroconverted early during the rearing period. Infections with M. hyopneumoniae acquired early during the rearing, presumably strengthened by secondary infections and environmental errors, was found to decrease the daily weight gain of the pigs. However, even non-complicated M. hyopneumoniae infections acquired late in the fattening period were associated with reduced daily weight gain. That growth reduction was estimated to be at least 60 g (about 6%) after adjusting for herd, pen, initial weight and sex.     

Relationship to growth performance of pneumonia and atrophic rhinitis lesions detected in pigs at slaughter among four seasons.

A commercial swine herd was selected for study, because pigs at slaughter repeatedly had lung lesions consistent with enzootic pneumonia and had snout lesions typical of atrophic rhinitis. Pigs born during various seasons of the year were allotted to 4 investigations and were evaluated from birth to slaughter. Individual lungs and snouts were identified and collected at the slaughter plant and later examined for gross lesions of bronchopneumonia and atrophic rhinitis, respectively. Each lesion was scored, and the following comparisons were made within investigations: prevalence and mean scores for lung lesions; prevalence and mean grades for snout lesions; correlations between lung lesion scores and growth indicators; correlations between snout lesion grades and growth indicators; and correlations between lung lesion scores and snout grade scores. Included in the growth indicators were average daily gain during the growing phase, average daily gain during the finishing phase, average daily gain during growing and finishing phases, and days to attain 104.5 kg of body weight. Prevalence of lung or snout lesions, mean values for lung lesion scores, mean values for snout lesion grades, and mean values for the various growth indicators were tested for statistical differences among the 4 investigations. Prevalence of lung lesions was highest (96%) for winter-slaughtered and lowest (81%) for autumn-slaughtered pigs. Mean scores for lung lesions were 7% (summer), 5% (autumn), 9% (winter), and 16% (spring). Prevalence of snout lesions was highest (85%) for spring-slaughtered pigs and lowest (42%) for autumn-slaughtered pigs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of the effect of pneumonia detected during lifetime with pneumonia detected at slaughter on growth in swine

Pneumonia in swine has been studied mainly at slaughter or necropsy. However, when performing slaughter or postmortem examinations, assessment of the true prevalence or lifetime extent of pneumonia is at best speculative. Radiography was used to evaluate lungs from pigs 21 to 150 days old. Follow-up slaughter examination was performed on pigs 180 days old. Individual percentage of pneumonia observed over the life of each pig and at slaughter were added to yield lifetime pneumonia scores. A significant (P = 0.0001) negative effect of lifetime pneumonia on growth rate was found. By comparison, slaughter examination proved to be a poor indicator of lifetime pneumonia; lesions were found to progress and regress dynamically throughout the life of pigs.     

Occurrence of multidrug resistant Salmonella in antimicrobial-free (ABF) swine production systems

This cross-sectional study was conducted to determine the prevalence and antimicrobial resistance of Salmonella species in swine reared in the intensive (indoor) and extensive (outdoor) ABF production systems at farm and slaughter in North Carolina, U.S.A. We sampled a total of 279 pigs at farm (extensive 107; intensive 172) and collected 274 carcass swabs (extensive 124; intensive 150) at slaughter. Salmonella species were tested for their susceptibility against 12 antimicrobial agents using the Kirby-Bauer disk diffusion method. Serogrouping was done using polyvalent and group specific antisera. A total of 400 salmonellae were isolated in this study with a significantly higher Salmonella prevalence from the intensive (30%) than the extensive farms (0.9%) (P<0.001). At slaughter, significantly higher Salmonella was isolated at the pre- and post-evisceration stages from extensively (29% pre-evisceration and 33.3% post-evisceration) than the intensively (2% pre-evisceration and 6% post-evisceration) reared swine (P<0.001). The isolates were clustered in six serogroups including B, C, E1, E4, G and R. Highest frequency of antimicrobial resistance was observed against tetracycline (78.5%) and streptomycin (31.5%). A total of 13 antimicrobial resistance patterns were observed including the pentaresistant strains with ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, tetracycline resistance pattern observed only among isolates from the intensive farms (n=28) and all were serotype Salmonella typhimurium var. Copenhagen. In conclusion, this study shows that multidrug resistant Salmonella are prevalent in ABF production systems despite the absence of antimicrobial selection pressure. In addition, it also highlights the possible role played by slaughterhouse and other environmental factors in the contamination and dissemination of antimicrobial resistant Salmonella in ABF production systems.     

Phenotypic and genotypic heterogeneity of Campylobacter coli within individual pigs at farm and slaughter in the US

The aim of this study was to determine the phenotypic and genotypic diversity of multiple Campylobacter isolates (n = 3 per sample) present within individual (heterogeneity) pig faecal and carcass samples at farm and slaughter, respectively. We isolated 1459 Campylobacter coli (1110 on farm and 349 from slaughter) from 908 pigs and 757 carcasses and characterized them for their antimicrobial susceptibility profile to a panel of six antimicrobials using the agar dilution method. Overall, we detected a significantly higher Campylobacter prevalence at the farm (54.7%) than at slaughter (19%) level (P < 0.05). C. coli isolates were resistant most commonly to tetracycline (66.2%) and erythromycin (53.6%) while fluoroquinolone resistance was detected in isolates (n = 17) only from the farm level. Phenotypic diversity of C. coli isolates at the 4-fold minimum inhibitory concentration levels within the same sample was detected in 38.6% (n = 192) pigs and 40.2% (n = 58) carcass swabs with no significant difference between the two sources (P = 0.72). Phenotypic heterogeneity based on the antimicrobial resistance patterns was observed in 32.5% (n = 162) of the farm samples and in 30.5% (n = 44) carcass swabs at slaughter (P = 0.64). A subset of 40 isolates representing ten pigs and eight carcass samples (originating from separate pigs) were further genotyped by multi locus sequence typing. The observation of phenotypic diversity was replicated at the genotypic level, as it was highlighted by the 22 sequence types which represented the 40 isolates. In conclusion, we detected multiple C. coli subtypes from individual pig or carcass samples indicating unprecedented level of heterogeneity. Our study clearly signifies the importance of testing multiple colonies to make appropriate and valid conclusions in epidemiological-based studies.     

An abattoir-based case-control study of risk factors for mycobacteriosis in Norwegian swine

An outbreak of mycobacteriosis in swine herds in southwestern Norway from autumn 1986 to 1990 is described. The prevalence of generalised infection in the pigs was higher than usual during the outbreak resulting in the condemnation of 0.3% of the swine carcasses in 1987. A case-control study involving 35 herds (17 herds with more than two tuberculous pigs at slaughter and 18 herds with no evidence of infection at slaughter) showed that an increased risk of infection was linked to combined production with sows and slaughter pigs in the same herd. The presence of birds in the pig house was another contributing risk factor. The standard of the ventilation system, covering of the feed tank, cleaning of the house less frequently than once a year and use of litter were not associated with tuberculous lesions.     

Host determinants of pneumonia in slaughter weight swine

A prospective cohort study was undertaken in a farrow-to-farrow swine herd to describe patterns of pneumonia, and to identify host risk factors associated with the extent of pneumonic lesions in 2 weight groups of slaughter swine. The risk of coughing and pneumonic lesions increased with increasing age of pigs within the herd (P less than 0.0001). The age-specific prevalence of pneumonic lesions was low (2.7%) in pigs less than 16 weeks old at slaughter, but increased rapidly when pigs were between 16 and 22 weeks old (8.6 to 67.9%). After 22 weeks, the prevalence remained relatively constant at about 80%. Associations between possible risk factors and pneumonia were investigated by use of multiple-regression models. Age at weaning (less than 24 days) and birth weight (less than 1 kg) exerted small, but significant (P less than 0.002), effects on the extent of pneumonic lesions in pigs slaughtered at 30 to 50 kg live weight. For pigs slaughtered at 90 to 110 kg, pneumonic lesions were more extensive (P = 0.007) in pigs sired by Yorkshire boars than pigs sired by non-Yorkshire sires (Duroc, Hampshire, Chester White, or American Spotted). Other host factor variables including weaning weight and clinical diseases (atrophic rhinitis, diarrhea, and arthritis) were not associated with pneumonia extent in either weight group. Higher pneumonia percentages were also associated with reduced growth rates in the grower/finisher phase. Pigs sired by Yorkshire boars grew significantly (P less than 0.0001) more slowly from entry into shed 2 (mean, 38 kg) until about the time of exit (mean, 92 kg) than pigs sired by other breeds (747 g/d and 795 g/d, respectively).     

Epidemiological investigation of swine tuberculosis in Arizona.

Swine tuberculosis occurred in thirteen herds of swine in Arizona. Mycobacterium avium serotypes 1, 2, 4, 5 and 8 were isolated from tissues of affected animals. These serotypes are responsible for approximately 85% of the mycobacterial infections found in swine in the United States. Based on tuberculin skin test responses and examinations of tissues collected at slaughter, the source of infection in at least one of these herds, Herd A, was found to be infected sawdust and wood shavings used as bedding. This finding concurs with the reports of others. Tuberculin skin tests performed on slaughter pigs in Herd A showed a 97.1% correlation between the number of pigs responding to tuberculin and the number found to have tuberculous lesions at slaughter. No correlation of skin test response and presence of lesions was possible for individual pigs, but these results imply that the test may have value when used to determine prevalence of the disease in a herd of pigs.     

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.     

Pleuritis in slaughter pigs: Relations between lung lesions and bacteriology in 10 herds with high pleuritis

Pleuritis in slaughter pigs has increased in recent years in the Netherlands. The aim of the present study was to determine what respiratory pathogens were involved in pleuritis.In total, lungs of 968 slaughter pigs from 10 herds with high prevalence of pleuritis were morphologically examined for size, location, and type of lesions. Moreover, histology and bacteriology were performed.Examination of gross lung lesions showed 45% pleuritis, 14% pleuropneumonia and 38% catarrhal pneumonia. Peribronchiolar cuffing was found in 61 of 142 samples. Actinobacillus pleuropneumoniae was cultured from 22 lung samples from four herds. Pasteurella multocida was cultured from 55 lung samples in eight herds. No specific pattern with respect to the causal pathogens was found.In conclusion, no single infectious cause of pleuritis was found. A variety of infectious agents combined with environmental factors should be considered as a cause of pleuritis.     

Efficacy of an inactivated aqueous vaccine for the control of enzootic pneumonia in pigs infected with Mycoplasma hyopneumoniae

The efficacy of an inactivated aqueous vaccine against Mycoplasma hyopneumoniae was evaluated at two M hyopneumoniae-infected farrow-to-finish commercial farms (A and B) in Greece. In a prospective, randomised double-blind study, two groups on each farm received intramuscular doses of either the vaccine or the adjuvant when they were one and four weeks of age. The pigs were observed daily for clinical signs of disease; morbidity and mortality were recorded; and bodyweight was recorded at intervals. At slaughter, the lungs of the animals were examined and the chest cavities were examined for signs of pleuritis. No adverse reactions to the treatments were observed in any of the pigs. On farm A the vaccinated pigs were on average 6 kg heavier at slaughter, and on farm B they were on average 4 kg heavier; on both farms the average daily gain of the pigs was greater than that of the unvaccinated pigs. The prevalence and severity of enzootic pneumonia in the affected lungs were significantly lower in the vaccinated than in the unvaccinated pigs.     

Granulomatous lesions in lymph nodes of slaughter pigs bacteriologically negative for Mycobacterium avium subsp. avium and positive for Rhodococcus equi

The prevalence of granulomatous lesions in lymph nodes of pigs was studied. From January till August 2004 in two slaughterhouses in The Netherlands 2,116,536 pigs were examined for the presence of granulomatous lesions in the sub-maxillary lymph nodes. In 15,900 (0.75%) of these pigs, lesions could be detected. Nine farms with the highest incidence of lesions were selected for a more detailed pathological and bacteriological examination. On these farms, the prevalence of lesions in sub-maxillary lymph nodes ranged from 2.3 to 5.7% with a mean of 3.0%. From 1276 pigs that were sampled, 98 (7.7%) displayed granulomatous lesions in the sub-maxillary lymph nodes and one (0.1%) pig showed lesions in its mesenteric lymph node. Mycobacterium avium subsp. avium (MAA) could not be isolated from the lymph nodes of the 99 pigs with lesions and from a selection of lymph nodes (n = 61) of pigs without lesions. Rhodococcus equi was isolated from 44 out of 98 (44.9%) of the sub-maxillary lymph nodes with granulomatous lesions and from two mesenteric lymph nodes without lesions. A comparison of former studies and the current results indicate that the prevalence of MAA infections in slaughter pigs has strongly decreased over the last decade, whereas R. equi is highly prevalent. The high incidence of granulomatous lesions associated with the bacteriological presence of R. equi could be considered as a serious cause of misdiagnosis of MAA infections in cases where meat inspection is carried out by inspection for granulomatous changes of lymph nodes only.