Following the successful introduction of the Pig Health Scheme (PHS), 75% of pig farmers and their vets are getting back the slaughterhouse data and health reports on the prevalence of certain diseases found in their pigs. How best to interpret these data is important, as it is the way the scheme can be effectively used to assess the level of disease on the farm and benchmark it with other producers. An assessment, whether an intervention e.g. via vaccination or therapy should be introduced, can be made. Additionally, it can be used to check that any intervention is working. It is invaluable information and really should be used by the farmer and vet to improve the health of the herd and reduce the cost of production.
Enzootic pneumonia (EP) lesions on the lung are one of the more easily measured disease parameters to monitor and score. The disease is caused by Mycoplasma hyopneumoniae and is widespread in the national herd and exacerbates other respiratory problems caused by PRRS virus and PMWS/PCV-2 infections. To look at the effects of the disease on its own, we need to go back to data produced before the arrival of PRRSV and PMWS in the 1990's, when a lot of work was done on EP. In my early pig vet days, I was fortunate to work under Mike Muirhead of the Garth Vet Group and with Reg Goodwin of Cambridge University, who were considered experts in the disease and M. hyopneumoniae itself.
Reg Goodwin discovered that M. hyopneumoniae caused the disease and devised the scoring method we use (maximum score 55, which approximately relates to about 55% of the lung involved) (Goodwin and others, 1969). He also set up the early monitoring programmes for his high health (PHCA) herds. Mike looked at farms with different levels of enzootic pneumonia and recorded certain aspect of the disease, such as the percentage of pigs affected with the lesions and their effect on feed conversion efficiency (FCE) and mortality (Muirhead, 1980). I looked at the effects of the severity of EP lesions on individual pig growth rates in finishers (Burch, 1982), which is currently used as the basis of the assessments on growth rate in the PHS. Approximately, a herd average lung lesion score of 10 depresses growth rate by 5% (37.5g/day). Barbara Straw, from the US collated as many EP field trials as possible and confirmed the depressing effects of EP lesions on pig's growth but also related these to depression of FCE; a score of 10 reduces FCE by about 4.5% (Straw and others, 1989).
From these works, a disease cost model can be made using basic production parameters (see Table 1) to determine the potential cost of EP by severity of average lung lesions scores. Vaccination with a good oil-based adjuvanted M. hyopneumoniae vaccine will reduce lesions by about 67% under field conditions (Burch - unpublished data) so the improvement from vaccination is not nearly 100%, as sometimes claimed. This has to be built into the model, as well as the cost of the vaccine.
The cost of even a low average lung lesion score of EP (score 5) can be about £1/pig and this increases as the score rises. The disease and its effects are not usually eliminated by vaccines, so there is a residual effect of the lesions left. If the cost of the vaccine is added (£0.50 for a single shot) then the breakeven for vaccination is a lesion score of about 4, but as the initial disease score rises to 10 the cost benefit is clear (see Graph 1).
Graph 1. Cost of EP, the benefits of vaccination and cost/benefit break-even point for vaccination
Knowing what is the farm's average lung lesion score, allows the farmer and vet to know what intervention is required, if any, to bring the level of disease down to minimise its impact on production.
As Stewart Houston says, 'to join the Pig Health Scheme is the best £33/year a pig farmer can spend' and encourages the remaining 25% to join.
References:
Burch, D.G.S. (1982) The incidence and distribution of lung lesions, associated with enzootic pneumonia, in pigs from 2 farms, and the effect of the extent of these lesions on weight gain. Proceedings of the International Pig Veterinary Society Congress, Mexico City, mexico, p 95
Goodwin, R.F.W., Hodgson, R.G., Whittlestone, P. and Woodhams, R.L. (1969) Some experiments relating to artificial immunity in enzootic pneumonia of pigs Journal of Hygiene, Cambridge, 67, 465-476
Muirhead, M.R. (1980) Porcine pneumonia. Its differential diagnosis and the control of Mycoplasma hyopneumoniae infection. The Pig Journal, 6, 103-120
Straw, B.E., Tuovinen, V.K. and Bigras-Poulin, M. (1989) Estimation of the cost of pneumonia in swine herds. Journal of the American Veterinary Medical Association, 195, 12, 1702-1706
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Pig Diseases & Medication: Pig Technical Reviews
