Pleurisy in pigs: associated risk factors and impact on health, welfare and performance
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Research partners: University of Cambridge, Veterinary Laboratories Agency
Industrial partners: Bowes of Norfolk, BQP, Yorkwold Ltd.
Sponsors: BPEX., RCVS Trust Senior Clinical Training Scholarship
Project duration: 2008 – 2009
This project set out to generate evidence based approaches to the investigation and control of pleurisy in the UK pig population. The introduction of the British Pig Health Scheme and systematic monitoring of pathology in slaughter pigs has highlighted the prevalence of pleurisy. Data from BPHS up to 2006 indicated that 68% of all batches monitored were affected by pleurisy to some degree and 14% of all individual pigs monitored showed signs of pleurisy. However, while much work has been published on risk factors for respiratory disease in general, little has been published on the infectious and non-infectious factors that underlie this condition. Even less has been published on the economic consequences of pleurisy for the producer and processor. The core aims of this project were:
- To determine the relative importance of on-farm risk factors for pleurisy thereby informing new preventive strategies.
- To quantify the impact of pleurisy on:
- Production costs before and after processing.
- Objective measures of health and welfare during production.
- To assess the relative importance of the current known causal agents of pleurisy in the UK.
- To provide this information in a format suitable for knowledge transfer to producers, veterinarians, and processors.
Taking each of these aims in turn, our key findings in relation to on-farm risk or protective factors came from a carefully designed case control study of UK finisher units with consistently high or low pleurisy prevalence according to BPHS data. We found that managemental risk factors for pleurisy included production system type (especially farrow-to-finish systems), incomplete application or absence of all-in all-out production flow, and repeated mixing or moving of pigs between weaning and slaughter. Some managemental practices were protective and these included cleaning and disinfection of finisher accommodation between batches, and the allowance of down-time between batches for grower and finisher batches. Sourcing from a higher number of breeders by batch finishers in multi-site operations was a key risk factor in our prospective study. We found that pleurisy affected units were more likely to have experienced consistently raised mortality in post-weaning pigs, to have showed respiratory symptoms in pigs through the post-weaning period, to have reported disease due to Actinobacillus pleuropneumoniae, and finally to have experienced wasting associated disease during 2007. The important role of infectious disease was supported by strong associations between batches that had seroconverted (been exposed) to A. pleuropneumoniae, swine influenza, porcine reproductive respiratory syndrome virus (PRRSV), and Mycoplasma hyopneumoniae.
We found clear indications of the substantial economic impact of pleurisy (and associated respiratory diseases that were likely underlying the pleurisy). We showed that a simple measure of total pleurisy prevalence for a subset of 50 pigs was as informative as either a more complex calculation of a pleurisy index that measured both prevalence and severity, or an assessment of pleurisy using Meat Hygiene Service data collected for the entire batch (up to 5000 pigs). Through an extensive prospective survey of 80 batches of slaughter pigs (approximately 95,000 pigs) we found increasing pleurisy prevalence was associated with reduced carcase weight (measured after any trimming) and increased age at slaughter. Similarly, daily weight gain, calculated by 2 methods, was also adversely affected. Costs to the producer, for a typical 10% pleurisy prevalence at batch level were found to be in the order of 226p/pig (based on stated assumptions) – based on reduced carcase weight and increased age at slaughter. We found that post-weaning mortality rates on units with a long term consistent pleurisy problem were on average 3.3% greater than for unaffected units. This alone, has a significant impact on costs of production even though it may not be a direct consequence of pleurisy associated disease.
A substantial economic impact of pleurisy was also found at the processing stage which was largely driven by the necessary reduction in line speed, and associated staff costs, to permit adequate inspection and trimming. A representative batch with 10% pleurisy prevalence was estimated to result in additional processing costs of 29p/pig (based on assumptions).
Efforts to characterise relationships between pleurisy at slaughter and objective on-farm measures of health and welfare were limited to the observed relationships were frustrated by problems with the data collected in our prospective study. We found this on-farm data to be highly variable with a very strong integrator-specific influence. However, this should not diminish the useful information that we identified in our retrospective analysis (Part 1).
The third aspect of the project was to characterise the prevailing infectious agents involved in pig pleurisy in England and Wales and to optimize the approach to on-farm investigation of raised pleurisy prevalence. This work emphasized the strong link between pleurisy and underlying pneumonia and identified the traditional bacterial contributors to respiratory disease. However, we found strong evidence that viral infections such as PRRSV and especially PCV2 were underpinning pleurisy. Useful information on appropriate minimum ages (>9 weeks), ante mortem clinical findings (respiratory signs, lethargy, conjunctivitis), and group sizes of necropsy pigs (>6) was found in order to optimize the chances of a successful diagnostic outcome.
In conclusion, this work has provided clear messages on the managemental factors that can reduce or exacerbate pleurisy. The substantial cost of pleurisy and associated disease both to producers and processors has been highlighted, and recommendations for optimized investigation and diagnosis of farm-specific causes were developed. Together, this provides sufficient preliminary knowledge for producers to calculate the economic impact of disease on their own units, to plan investigations of their own infectious and non-infectious factors, and to implement protective management practices that are most suited to their specific circumstances. These key messages have been set out in Section 7 as knowledge transfer notes.
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Press release (May 09)