30 November 2001

HYGIENE KEY TO KEEPING PMWS UNDER CONTROL

Postweaning multisystemic wasting syndrome and porcine

dermatitis and nephropathy syndrome are spreading.

Pig vet Neville Kingston discusses control methods, based

on a study of 43 affected units in his practice

A CONTROL strategy for reducing the incidence of pig wasting diseases must centre on improving the units hygiene and production system.

The disease is usually observed as PMWS at 7-12 weeks of age with infected pigs looking distressed, pale, jaundiced and scouring. As pigs are recovering from PMWS, PDNS is commonly seen as spots or purple patches on the skin.

The disease has devastating effects on feeding herd performance, with mortality doubling or trebling and weight variations within age groups. Higher mortality, longer emptying times, extra accommodation for sick pigs and drug treatments result in falling farm incomes.

After reviewing 43 cases of PMWS/PDNS in the practice, a comparison of herd mortality was made to explain wide variations seen in mortality and pig growth rates.

The most striking trend within affected herds was a series of disease problems in the growing herd over two months, with mortality gradually increasing, before clinical PMWS was observed.

Once disease was diagnosed clinically and confirmed by post mortem and histology, the usual growing herd mortality doubled or trebled. Then mortality decreased over 3-6 months, depending on the diligence of unit staff to bring disease under control.

Mortality rates

Mortality rates varied within affected herds. Higher mortality was seen on units with poorer health status, particularly those suffering with major diseases, such as enzootic pneumonia and porcine reproductive and respiratory syndrome (PRRS). However, the health status of a unit is relatively difficult to change.

Vaccination can help reduce incidence of endemic disease. However, some scientific literature indicates vaccines may over-stimulate piglets immune systems, so it is important vaccination is carried out well before PMWS is observed.

Experience on farm shows a reasonable response to water soluble antibiotics for groups starting to waste and individual injections for clinically ill pigs. But various immune system enhancers in feed have given variable results.

Generally, herds with a high level of stockmanship have low mortality, but the survey shows with PMWS/PDNS there is no evidence of reduced mortality – it was higher in many cases.

There was also a link between the hygiene system adopted on the unit and mortality. The stricter the hygiene – all-in/all-out, batch production, streaming of sick pigs and washing between batches – the lower the mortality.

One large outdoor unit, finishing pigs on three different systems, clearly demonstrated the effect of production system and hygiene on performance.

Pigs were weaned weekly. Those pigs moved to an off-site straw yard at 7kg and not moved until slaughter had a mortality of 3%. Pigs that went off-site into a straw yard nursery and moved at 30-35kg to finishing yards had a higher mortality of 6-8%.

This variation in mortality depended on whether nursery yards had been washed out prior to weaners entering and the standard of weaner care, particularly in the first 10 days post weaning. Mortality was also higher when pigs were just starting with PMWS as they moved from the nursery to the finishing yard.

Mortality varied between 7% and 10% in another finishing system on the unit. Pigs were kept in a continuously populated site, with four batches on the site. Initially weaned into veranda pens, 25kg pigs were then moved into one of three finishing houses – two straw yards and one part slatted.

Units adopting strict hygiene measures (see panel) usually reduce mortality to reasonable levels – 1.25-1.5 times the original overall mortality of the unit. In some cases mortality levels fell below levels prior to PMWS.

Once PMWS emerges on a unit, the level of endemic disease explodes. It is only with diligent implementation of hygiene measures that disease is brought under control. Although it is a long hard process, it can be achieved. The disease can depress stockpeople, as it is often overwhelming, but with constant support it can be achieved.

When the health status of a unit is particularly poor, the disease is more difficult to control. Depopulation and restocking may have to be considered or at least going to three week batch production and strict separation by housing different age groups. &#42

Do not move pigs between seven and 12 weeks of age and operate a strict all-in/all-out hygiene policy to reduce incidence of pig wasting diseases on affected units, advises Neville Kingston (inset).

HYGIENE/PRODUCTION SYSTEMS TO REDUCE PMWS

&#8226 Do not move pigs between seven and 12 weeks of age – the prime age for developing PMWS.

&#8226 Carefully consider sources of breeding stock. Isolate and acclimatise them over an eight week period.

&#8226 Operate a strict all-in/all-out policy by introducing a batch or weekly production system.

&#8226 All pigs must be weaned each week. Do not mix pigs from different weekly batches.

&#8226 No movement of pigs between each batch.

&#8226 Remove sick pigs from pens immediately and move to sick pens.

&#8226 Build new sick pens – outdoor weaning huts are commonly used.

&#8226 Make up a new sick pen each week.

&#8226 Periodically empty sick pens.

&#8226 Never remix in recovered sick pigs.

&#8226 Keep each batch in separate air space and ensure air does not enter from other rooms/houses.

&#8226 Wash out and disinfect rooms between batches.

&#8226 Only use a disinfectant with products of proven activity for circovirus.

&#8226 Consider partial depopulation of problem areas.

&#8226 Reduce pig movements from weaning to slaughter.

&#8226 Reduce stress, particularly check ventilation.