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Classifying Swine Herds by Porcine Reproductive and Respiratory Syndrome Virus Status

13 May 2016

Global PRRS Solutions - Boehringer Ingelheim

The purpose of this paper is to provide a herd classification system for describing the PRRSV status of herds, based upon a set of definitions reflecting the biology and ecology of PRRSV.

An accepted set of terms and herd clas­sifications will facilitate regional and national efforts to eliminate PRRSV. Furthermore, the availability of standardized nomenclature will allow communi­cations among researchers, veterinarians, producers, genetic companies, and other industry participants.

How is it done?
This herd classification system was developed by a definitions committee formed jointly by the American Association of Swine Veterinar­ians (AASV) and the United States Depart­ment of Agriculture PRRS-Coordinated Agricultural Project, and was approved by the AASV Board of Directors on March 9, 2010. The committee included veterinarians from private practice and industry, research­ers, and representatives from AASV and the National Pork Board.

What are the results?    
Breeding herds, with or without growing pigs on the same premises, were categorized as Positive Unstable (Category I), Positive Stable (Category II), Provisional Negative (Category III), or Negative (Category IV) on the basis of herd shedding and exposure status. Growing-pig herds are categorized as Positive or Negative.

What implications does this paper have?

Standardized nomen­clature will facilitate better contractual and business arrangements, especially those between genetic and commercial production companies and agreements between produc­ers that offer premiums for weaned pigs from breeding-herd sources with a specific PRRSV status.

Researchers writing proposals and papers and making presentations may save time otherwise spent defining terms related to PRRSV, and standardized definitions will facilitate comparison of field-based research results by making clearer the conditions under which research trials are conducted. 

However, anecdotal evidence from the field supports the notion that herds classified as Positive Stable (II) have better reproductive and growing-pig performance than herds that are Positive Unstable (I).

Being Positive Stable (II) is the goal for breeding herds that are trying to control the virus. In the context of area or national elimination efforts, subdivision of category II into II-A and II-B is important to convey the likely differences in the risk of current or future shedding of virus by animals in these herds.

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