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Valuable improvements in growth rate and feed efficiency are reported from Chile, for units where the PRRS virus has been eliminated. (Photos courtesy of Asprocer, Chile)
on June 30, 2009

Chile eradicates PRRS

National eradication of the virus from Chile's herds moved close to completion when the last batch of positive animals went for slaughter in April this year

Chile is close to becoming the first country in the world to eradicate PRRS virus infection. In April of this year the last group of PRRS-positive animals was slaughtered. To declare farms free from PRRS it is necessary to cull all sows present in their herds at the time of infection.

Eradication is a highly significant event, not least for the country's foreign trade in pigmeat. Chile exports pork to several markets around the world. In 2006, the value of the meat exported by the industry amounted to more than US$300 million. This is expected to reach US$600 million by 2010, due to the considerable investments being made by local companies in production and export development.

Then there is the fact that Chile can claim to have more free trade agreements with other countries than any other pork exporter. This point is a big advantage for a pig industry that boasts an excellent health status: both foot-and-mouth disease and classical swine fever/hog cholera having been eradicated in the past.

Nationwide survey

For PRRS, the idea of starting a nationwide programme of eradication was raised in 2001 after the animal health division of the Ministry of Agriculture's agricultural and livestock service (SAG Chile) carried out an epidemiology study on PRRS serology by taking blood samples from pigs on the largest farms nationally. Sampling was done at 93 herds. From a total 2011 samples, the study identified 214 (11.9%) as positive using the ELISA immunoassay technique. These positive samples came from 28 pig units, or 30.1% of all the farms studied.

The initial testing confirmed the isolation of the virus strain. Genomically, this was confirmed as being 88.9% similar to the American reference strain VR 2332 and very distant from the European strain of the virus.

The decision to begin implementing the eradication programme was taken in 2001, soon after the information from the study became known. Major considerations behind the decision were that Chile had a genetic pyramid to support re-stocking and most of its pig population was free from the PRRS virus.

From the outset, eradication was in fact a joint venture. The programme involved SAG as the public veterinary authority, Chilean pork producers association Asprocer, privately owned pig enterprises and a number of private veterinary and commercial companies.

Setting the strategy

In the beginning, a technical committee was formed with representatives of the public and private sectors of the pig industry. Some of the most important decisions made at the start included making PRRS a notifiable disease so that the eradication exercise could receive the legal support it crucially required. Under the public-private agreement between SAG and Asprocer, official eradication would be regulated by SAG. Also agreed was that no PRRS vaccination would be available to the country's herds.

The strategy to eradicate the virus on a national basis began with its attrition on multi-site enterprises, using a procedure described in 2000 by a study group that had included the programme's international consultants Dr Montserrat Torremorell and Dr Steve Henry. Site 1 of the enterprise would be kept closed for 6 months to stabilise it while sites 2 and 3 would undergo total or partial depopulation. A protocol of depopulation-repopulation was followed for single-site units.

Among other measures, surveillance of the virus-negative population was performed at the auction market. Biosecurity and control received great emphasis at the positive farms. Moves also were made to improve import regulations and controls. Further investigation took place of the virus genome. What is more, probably for the first time anywhere, geo-satellite positioning (GPS) was used to identify the location of 100% of the farms in Chile involved in industrial pig production.

See from Table 1  how progress evolved in eliminating the PRRS virus from both mono-site and multi-site farms across all of Chile. In the case of mono-site units the depopulation and repopulation procedure was done in 2005. The mono-site producers joined together to rent one empty farm where they could establish a new herd of 2000 PRRS-negative sows for repopulating their cleaned-up and disinfected units.

Before that, however, there had been a problem in 2003 when a number of multi-site farms experienced a new PRRS outbreak. The opportunity for the virus to enter these sites was attributed to a failure on the part of producers or farm workers to observe the biosecurity rules that had been specified.

Comparing Figure 1  and Figure 2  shows the reduction in the number of infected sows at national level between the start of the programme in 2001 and the situation recorded in 2006. Today, no sows are infected. But Chile still has had to deal with sows that were present when some multi-site farms were infected. Those farms have followed a strict sow culling procedure to complete the eradication protocol.

Of course, PRRS is an expensive disease for herds that suffer its effects and in terms of the actions needed to eradicate it. In Chile the cost of the disease has been estimated on one multi-site farm after the infection. Taking into account the impact on production results and the cost of eliminating the virus, the estimate is that the total reached US$2800 per sow.

A number of valuable benefits to the Chilean pig industry can be set against such high costs. Eradicating PRRS has already brought an improvement in production results after mono-site units were repopulated. They have seen increased daily weight gains, better feed conversion and a reduction in mortality rate across all production stages. With a reduced prevalence of secondary disease such as respiratory and digestive problems, it has meant an improved profit per pig sold.

It can also now be said that the eradication programme to beat PRRS has increased the profitability of all previously infected farms. This is due to a lower mortality rate and less use of antibiotics, as well as to better feed efficiency and fewer days to reach market weight.

Add to that the excellent experience of working together by the public veterinary authority, Chilean pork producers and private companies. This has presented a good example to show it is possible to obtain good results from the eradication of diseases and to improve safety levels and wholesomeness of final products.

Chile also wins. Increased biosecurity levels now apply on all farms and better control is now in place for the entry into the country of animals or biological products that originate from other places. Ultimately, there is the big advantage that the Chilean pig industry has value-added pork for export to markets around the world because the eradication of PRRS means healthier and safer animals. PIGI

 

This report has been specially prepared for Pig International by the directors of Chilean pig producers' association Asprocer

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The strategy to eradicate PRRS has involved depopulating the nursery and grow-out sites of multi-site units while keeping the sow herd closed to stabilise its status.
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