Helle Stege

Prevalence of intestinal pathogens in Danish finishing pig herds

Our aim was to determine the prevalence of the intestinal bacteria: Lawsonia intracellularis, Brachyspira hyodysenteriae, Serpulina intermedia, Brachyspira innocens, Brachyspira pilosicoli, pathogenic Escherichia coli (serogroups O138, O139, O141 and O149) and Salmonella enterica in Danish finishing pig herds. A total of 79 herds was randomly selected and visited during 1998. From each herd, 20 faecal samples were collected from individual pigs weighing 30-50kg. Furthermore, 10 pooled pen samples were collected and examined for S. enterica. In total, 1580 faecal samples and 790 pen samples were collected and examined by polymerase chain reaction (PCR) or culture. L. intracellularis was found in 74 herds (93.7%), B. hyodysenteriae in two herds (2.5%), S. intermedia in 10 herds (12. 7%), B. innocens in 27 herds (34.2%), B. pilosicoli in 15 herds (19. 0%), pathogenic E. coli in 19 herds (24.1%) and S. enterica in eight herds (10.1%). The within-herd prevalences of L. intracellularis and B. hyodysenteriae were 25-30%; the within-herd prevalences of the other agents were 5-10%. Three herds (4%) were not infected with any of the bacteria and 25 herds (32%) were only infected with L. intracellularis.

Risk factors for intestinal pathogens in Danish finishing pig herds

The objective of this investigation was to identify risk factors for infection with the intestinal bacteria: Lawsonia intracellularis, Brachyspira hyodysenteriae, Serpulina intermedia, Brachyspira innocens, Brachyspira pilosicoli and swine-pathogenic Escherichia coli (serogroups O138, O139, O141 and O149) in Danish finishing pig herds.A total of 79 herds was randomly selected and visited during 1998. From each herd, 20 faecal samples were collected from individual pigs weighing 30-50 kg. In total, 1580 faecal samples were collected and examined by polymerase chain reaction (L. intracellularis) or culture (all other agents). Information on feed and management procedures was collected by filling in questionnaires at the herd visits. The questionnaires included information on 29 dichotomous variables and three continuous variables. Variables with P<0.25 in a preliminary screening (chi2- or t-test) were selected for the statistical modelling. Our conclusions, based on the results of multifactorial logistic regression (cut-off: P=0.05), were the following: 1. Consistent batch production was associated with reduced prevalences of L. intracellularis and weakly -haemolytic spirochetes (S. intermedia, B. innocens, B. pilosicoli) (ORs=0.43 and 0.06, respectively). 2. Home-mixed (and/or non-pelleted) feed was associated with reduced prevalences of L. intracellularis and weakly -haemolytic spirochetes (ORs=0.6 and 0.4, respectively). 3. Providing straw to finishers was associated with a reduced prevalence of weakly -haemolytic spirochetes (OR=0.28-0.32). 4. Not using antimicrobial growth promoters for piglets was associated with an increased prevalence of S. intermedia (OR=11.11). 5. Rare occurrence of post-weaning diarrhoea (as opposed to common) was associated with an increased prevalence of weakly -haemolytic spirochetes (OR=8.3-13.7).

Diagnostic Performance of Different Fecal Lawsonia intracellularis—Specific Polymerase Chain Reaction Assays as Diagnostic Tests for Proliferative Enteropathy in Pigs: A Review:

Traditionally, diagnosis of Lawsonia intracellularis—associated proliferative enteropathy (PE) has depended on necropsy and histology. Since the establishment of the etiologic role of L. intracellularis, a number of specific polymerase chain reaction (PCR) assays have been developed for the detection of DNA in feces. The present article is a systematic review of peer-reviewed publications on the application of L. intracellularis specific fecal PCR as an antemortem diagnostic test for histologic lesions of PE in pigs. Based on this information, a range of diagnostic sensitivities (36-100%) and specificities (50-100%) of the published tests was calculated. Validity and confidence limits of the estimates varied considerably. The positive and negative predictive values of 6 different PCR assays were calculated for PE prevalence of 15%, 30%, 45%, 60%, 75%, and 90%, using a histologic case definition of PE and based on the reported test sensitivities and specificities. The simulated predictive values suggested that applying the fecal PCR assay as a diagnostic test is more likely to overestimate than underestimate the number of pigs having histologic lesions of PE under field conditions.

Association between average daily gain, faecal dry matter content and concentration of Lawsonia intracellularis in faeces

BackgroundThe objective of this study was to investigate the association between average daily gain and the number of Lawsonia intracellularis bacteria in faeces of growing pigs with different levels of diarrhoea.MethodsA longitudinal field study (n = 150 pigs) was performed in a Danish herd from day 29 to 47 post weaning. Every third day all pigs were weighed, subjected to a clinical examination and faecal samples were obtained. Faecal samples were subjected to dry matter determination and absolute quantification by PCR for L. intracellularis and porcine circovirus type 2 (PCV2). Association between average daily gain, faecal dry matter content, numbers of L. intracellularis bacteria and PCV2 genome copies in faeces was investigated in a multilevel mixed-effects linear model.ResultsIncreasing numbers of L. intracellularis log10 bacteria/g faeces were significantly associated with decreasing average daily gain (P < 0.001). The association was decreasing with increasing faecal dry matter content (P < 0.01). The number of PCV2 log10 copies/g faeces was not significantly associated with average daily gain of the pigs (P > 0.5).ConclusionThe results suggest a potential application of a PCR quantifying L. intracellularis in growing pigs. Faecal dry matter content must be taken into consideration in interpretation of such test results.

Evaluation of a microwave method for dry matter determination in faecal samples from weaned pigs with or without clinical diarrhoea

Microwave drying as a procedure for determination of faecal dry matter in weaned pigs was evaluated and clinical relevant cut-off values between faecal consistency scores were determined. Repeatability and reproducibility were evaluated. Overall coefficient of variation was 0.03. The 95% confidence limits for any future faecal subsample examined by any operator in any replica were ± 0.85% faecal dry matter. Robustness in relation to weight of wet faeces was evaluated. The weight categories were 0.5, 1.0, 1.5, 2.0 and 3.0 g. Samples of 0.5 g gave significantly different mean faecal dry matter content compared to weighing of 1.0-3.0 g. Agreement with freeze-drying was evaluated. Lins concordance correlation coefficient was 0.94. On average the faecal dry matter values was 1.7% (SD=1.99%) higher in freeze dried compared to micro waved samples. Non-parametric ROC analyses were used to determine optimal faecal dry matter cut-off values for clinical faecal consistency scores. The 4 consistency scores were score 1=firm and shaped, score 2=soft and shaped, score 3=loose and score 4=watery. The cut-off values were score 1: faecal dry matter content >19.5%, score 2: faecal dry matter content ≤ 19.5% and >18.0%, score 3: faecal dry matter content ≤ 18.0% and >11.3%, score 4: faecal dry matter content ≤ 11.3%. In conclusion, the microwave procedure has an acceptable repeatability/reproducibility and good agreement with freeze drying can be expected. A minimum of 1.0 g of wet faeces must be used for analyses. Faecal dry matter cut-off values between 4 different clinical consistency scores were determined.

Diagnostic performance of fecal quantitative real-time polymerase chain reaction for detection of Lawsonia intracellularis–associated proliferative enteropathy in nursery pigs

Quantitative polymerase chain reaction (qPCR) tests for detection and quantification of Lawsonia intracellularis in feces from pigs have been developed. The objective of the current study was to evaluate the diagnostic performance of a fecal qPCR test for detection of nursery pigs with L. intracellularis–associated proliferative enteropathy (PE) under field conditions. Furthermore, the diagnostic performance for different subpopulations of pigs was investigated, including pigs infected or noninfected with Porcine circovirus-2, Brachyspira pilosicoli, and Escherichia coli. The diagnostic performance was evaluated in terms of diagnostic sensitivity and specificity. Data from pigs originating from 20 herds with antibiotic treatment requiring diarrhea outbreaks from a prior study were reused. Before treatment, pigs were randomly selected for histological and immunohistochemical examination of intestinal segments and fecal quantification of L. intracellularis by qPCR. A total of 313 pigs (157 without diarrhea, 156 with diarrhea) were included in the statistical analysis, and 37 pigs (11.8%) were classified as PE positives (defined as proliferative histological lesions in combination with L. intracellularis demonstration by immunohistochemistry). Lawsonia intracellularis was detected by qPCR in feces from 91 pigs (29.1%). A nonparametric receiver operating characteristic (ROC) analysis provided an area under the ROC curve (0.93) and an optimal cutoff value of 4.8 log10 L. intracellularis bacteria/g feces. This cutoff provided a diagnostic sensitivity of 0.84 and diagnostic specificity of 0.93. The diagnostic sensitivity and specificity were significantly different between herds (P < 0.0001). Numerically, diagnostic sensitivity and specificity were different between subpopulations of pigs, but no significant differences were demonstrated.

Observations of variable inter-observer agreement for clinical evaluation of faecal consistency in grow-finishing pigs.

Inter-observer agreement for assessment of faecal consistency in pigs was evaluated using a scoring system with 3 categories. In a pilot study, 3 observers performed an examination of faecal samples post-collection. The samples were obtained from pigs (12-13 weeks old) in 4 herds with a history of diarrhoea associated with Lawsonia intracellularis, Brachyspira spp. and/or Porcine Circovirus Type 2. Observer 1 examined all the faecal samples from the 4 herds. Observer 2 only examined the faecal samples from herds 1 and 2. Observer 3 only examined the faecal samples from herds 3 and 4. We observed a substantial agreement in faecal consistency scores between Observers 1 and 3 (kappa=0.64, 95% CI: 0.51-0.78). In contrast, only a fair agreement was observed between Observers 1 and 2 (kappa=0.24, 95% CI: 0.14-0.34). The variations in inter-observer agreement detected in the current study suggest that misclassification error can be a problem in studies assessing faecal consistency. Solutions may include developing a standardized system for scoring the consistency of pig faeces, calibration when more than one observer is involved in clinical studies and using a more objective measure of faecal consistency.

Effect of breeding strategy and feeding system on the within-herd variation of lean meat percents in Danish slaughter pigs

In several countries slaughter pigs are paid for individually, according to slaughter weight and lean meat percent (LMP). Production of uniform batches of pigs within the optimal weight and LMP limits will obtain the best price. Therefore, all pigs should have a similar growth rate (average daily gain, ADG) and reach an appropriate slaughter weight within the same time period. LMP may serve as a proxy for ADG since pigs with low LMP have significantly higher ADG than pigs with high LMP and vice versa. Both breeding strategy and feeding system may influence the range of variation among pigs. The aim of this study was to test the two following hypotheses: (1) Herds purchasing breeding gilts have a higher mean value and a lower variation (standard deviation) in LMP than herds producing their own breeding gilts and (2) Herds using restricted feeding of finishers have a higher mean value and a lower variation (standard deviation) in LMP than herds with ad libitum feeding of finishers. The study included 72 herds and a total of 345,132 pigs slaughtered during one year. Among the 72 herds, 40 were home-breeders and 32 purchased breeding gilts from a breeding company. Nineteen herds used restricted feeding, of which 8 (42%) were home-breeders. Fifty-three herds used ad libitum feeding, of which 32 (60%) were home-breeders. Breeding strategy had a significant effect on SDLMP (p=0.003), where purchase of breeding gilts resulted in a significantly lower standard deviation of the monthly LMP compared to home-bred gilts (a difference in median SDLMP of 0.2 percentage points or 8% difference between groups). Feeding system had a significant effect on the meanLMP (p<0.001), with a significantly higher meanLMP in herds using restrictive feeding compared to ad libitum feeding (60.7% versus 60.0%). Restrictive feeding also resulted in a significantly lower SDLMP (p<0.001) compared to ad libitum feeding (2.2% versus 2.5% or a 12% difference between groups).

Association between lean meat percentage and average daily weight gain in Danish slaughter pigs

Danish pigs that are within optimal weight limits and have a high lean meat percentage (LMP) obtain the best prices at slaughter. Another reason to consider the variation in LMP is the assumed association between LMP and average daily weight gain (ADG) at the individual level. The aim of this study was to test whether high ADG was associated with low LMP and vice versa. A cohort of 99 pigs from a conventional Danish herd was followed from 30kg to slaughter. The data included days in the herd, start- and end-weights, calculated ADG and LMP, reported from the abattoir. The study also included existing data from 13,057 boars from a Danish boar test station. The results of the study demonstrated a significant negative association between LMP and ADG: Pearsons correlation coefficient (r)=-0.42 (95% CI: -0.57; -0.24) (p<0.0001) for the cohort and r=-0.42 (95% CI: -0.48; -0.36) (p<0.0001) for the boars.

Within-day repeatability for absolute quantification of Lawsonia intracellularis bacteria in feces from growing pigs

Absolute quantification of Lawsonia intracellularis by real-time polymerase chain reaction (PCR) is now possible on a routine basis. Poor repeatability of quantification can result in disease status misclassification of individual pigs when a single fecal sample is obtained. The objective of the current study was to investigate overall variation within a day for fecal numbers of L. intracellularis bacteria determined by real-time PCR in growing pigs. From each of 30 pigs with an infection of L. intracellularis, 5 fecal samples were collected within 1 day. A total of 150 fecal samples were obtained and subjected to quantitative PCR (qPCR) testing. Mean fecal dry matter content was 14.3% (standard deviation = 4.5%). Two pigs (6.7%) alternated between being L. intracellularis qPCR positive and negative. For 28 pigs, the excreting levels of L. intracellularis were within the dynamic range of the qPCR assay at all sampling points. For these 28 pigs, the mean excretion level of L. intracellularis was 6.1 log10 bacteria/g feces (standard deviation = 1.2 log10 bacteria/g feces). The maximum observed difference between 2 fecal samples from the same pig was 1.1 log10 bacteria/g feces. The average standard deviation for individual pigs was 0.27 log10 bacteria/g feces. The average coefficient of variation within pigs was 0.04, ranging from 0.006 to 0.08. The results imply that absolute quantification of L. intracellularis by qPCR has acceptable repeatability within 1 day. However, a population-specific proportion of pigs alternating between positive and negative test results must be expected.