NADIS Veterinary Report & Forecast - April 2009

by 5m Editor
18 May 2009, at 8:19am

UK - This is a monthly report from the National Animal Disease Information Service (NADIS), looking at the data collected from their UK farm inspections.

Pleurisy is a pathological condition widely seen in pigs at slaughter – and at post mortem examination on farms – and results in the adhesion of lung tissues to themselves and to the chest wall. In severe chronic cases the damage is so great that it is impossible to remove the pluck from the carcase, leading to delays in slaughter line dressing and possibly condemnation.

It is not caused by any one infection – a range of organisms can be involved either as primary agents (Actinobacillus pleuropneumoniae, Haemophilus parasuis – Glässers Disease) or as secondary bacteria taking advantage of previous lung damage. Pasturella, Arcanobacter and Streptococcus suis are common isolates.

Pleurisy can be of recent origin – fibrinous – long-standing (fibrous) or septic where abcessation complicates the adhesions. At slaughter, pleurisy is scored (under BHPS) as mild – affecting only a small part of the pluck – or extensive where more than 25 per cent lung tissue is affected. The nature and severity of the pleurisy will dictate the clinical impact on the pig, with mild disease having little measurable effect but severe lesions being associated with illness and loss of growth.

In any single case, it is almost impossible to estimate the time of the initial infection (other than in very recent cases). The condition can start at any stage of the growing cycle.

The BPHS will have data – to be published – covering the whole country, but NADIS on-farm surveillance has the ability to look at systems and geography in an attempt to highlight predisposing factors.

However, it is surprising and disappointing to see that within this data there has been a rise in recorded pleurisy levels through this last winter (peaking at 9 per cent of pigs) which represents the time when widespread vaccination of pigs for PCV2 has filtered through to slaughter. (Graph 1.)

However, within the data set, a number of interesting patterns can be discerned:

  • Herd size effects. Within the NADIS population, levels of pleurisy at slaughter are dramatically higher (ten per cent versus three per cent) in larger sites containing over 4000 pigs. This tends to suggest that disease load follows population size. (Graph 2.)
  • Source of growing pigs. (Graph 3.) Within the data set, outdoor derived pigs have four times the prevalence of pleurisy than indoor derived pigs. This may result from a healthier outdoor rearing environment actually leaving pigs more naïve when they come to finishing. Resultant disease challenge may have a greater effect on them compared to pigs that have had a steady challenge since birth.

The high prevalence of disease within East Anglia (graph 4) is consistent with the high number of outdoor producers in that area, with the differences between the two major pig-keeping areas dramatic.

  • System effects. Within the surveyed population, pleurisy levels are almost double on straw systems compared to slats. This confirms previous observations that straw-based systems are not necessarily better for respiratory health although this data may be confounded by the “outdoor effect” and East Anglian excessive disease levels as straw may be the predominant housing type here.

Pig flow appears to make a major difference to pleurisy levels, continuous flow systems revealing three times more pleurisy than batch systems, as would have been expected (Graph 3).

The University of Cambridge has recently completed a BPEX-funded research project looking in detail at pleurisy on-farm and at the abattoir and results of the study will be reported later.

5m Editor