In the UK, the national herd has been suffering from Post-weaning Multisystemic Wasting Syndrome (PMWS) since the first cases appeared in 1999. The acute disease with high mortality has largely passed (see Table 1 and Graph1) and we are now living with the chronic form of the disease. At its peak in 2003, the national average herd mortality was 13.8% (BPEX, 2006) for weaners, growers and finishers. The previous rolling average, pre-PMWS, was 5.7%, therefore there was an additional 8.1% mortality associated with the disease and its consequences. Even in 2005, the average national herd mortality is 9.9%, 4.2% over what it used to be before PMWS. This really can be considered a national tragedy for both the health and welfare of UK pig production.

Table 1. National average mortality (%) in weaner/growers and finishers 1998-2005

Graph 1. National average mortality (%) in weaner/growers and finishers 1998-2005

(Source: (BPEX 2006)

So where are we today? The disease has spread across the UK and some veterinarians think that 80% of their herds have been affected. Now, we are seeing a fall in the mortality in the weaner/growers, probably associated with an increase in sow immunity and the protective effect of passive immunity given in the colostrum, as well as improved husbandry (28 day weaning age) and hygiene measures, according to the Madec principles. The average mortality has dropped in the younger pigs to 3.4%, 1.0% above the rolling mean before PMWS. However, the average mortality in finishing pigs has plateaued at 6.5%, on average 3% higher than it was before PMWS and there are still some herds getting upto 10% mortality in batches going through.

The main cause of the disease and its effects, not only on mortality but reductions in growth rate and feed conversion efficiency (FCE), is now clearly associated with Porcine Circovirus type 2 (PCV-2) infection. In both the USA and Canada there has been a dramatic response to the PCV-2 vaccines, which are being used there, both in sows and especially piglets. There are thought to be other associated trigger/complicating factors such as Mycoplasma hyopneumoniae, PRRSV (Porcine Reproductive and Respiratory Syndrome Virus) and even Salmonella spp, which exacerbate the clinical problem and on-going work, is looking at the impact of these concurrent infections on the expression of the disease.

Using figures and costs from our own UK production trials (Burch and others, 2006) and comparing these with some of the responses to piglet vaccination with a killed PCV-2 vaccine (Desrosiers and others, 2007) where finisher mortality fell from 9.4% to 2.4% in vaccinated pigs, a cost/benefit model for finishers was developed. The vaccine (Ingelvac CircoFLEX - Boehringer Vetmedica) was used in batches of weaner and grower pigs and the performance was monitored during the finisher period. The pigs were free of PRRS and enzootic pneumonia, so the impact was primarily on PCV-2 infection.

Table 2. Cost of PCV-2 associated disease in finishers by severity and cost/benefit model results based on piglet vaccination

A severe form of the PMWS, losing an additional 7% mortality in finishers, would cost £11.28/pig produced in just lost production, let alone carcass disposal and medication costs. Even the national average of 3.0% additional mortality associated with PCV-2 infection in finishers is costing the industry £4.77/pig produced or £42million pounds/year. It is no wonder that the UK industry, with one of the highest pig mortality rates in Europe, is finding it difficult to compete with our EU neighbours.

Graph 2. Cost of disease (£) based on PCVD associated mortality in finishers and potential vaccination costs

It is likely that the piglet vaccines will not be available for some time in Europe but one can see that in the UK especially, with our straw-based finishing systems, there is a desperate need for such vaccines.

References:
BPEX (British Pig Executive) (2006) Pig Yearbook 2006 pp 47-50

Burch, D.G.S., Webster, G.I.A., Morgan, M., Macdonald, M. and Klein, U. (2006) Comparative efficacy of Tiamutin and Lincospectin in the drinking water for the treatment of mixed enteric and respiratory infections in finishing pigs. Proceedings of the 19th International Pig Veterinary Society Copenhagen, Denmark, 2, p 343

Desrosiers, R., Clark, E., Tremblay, D. and Tremblay, R. (2007) Preliminary results with Ingelvac® CircoFLEX™ to protect multiple ages of Quebec pigs against PCVAD. Proceedings of the American Association of Swine Practitioners Conference Orlando, USA, pp 143-145

Pig Diseases & Medication:  Pig Technical Reviews

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