The PRRS Host Genetics Consortium (PHGC) has undertaken a major study of genetic resistance to porcine reproductive and respiratory syndrome (PRRS) virus.

The group is working to identify new genes and mechanisms of PRRS resistance or susceptibility in order to help pig breeding companies produce more disease-resistant pigs.

Funded by the Pork Checkoff, Agricultural Research Service scientists collaborated with Kansas State University (KSU) and Iowa State University researchers to complete eight infection trials of 1,600 pigs to assess the role of genetics in PRRS virus resistance.

USDA’s PRRS Coordinated Agricultural Projects provided additional funds to uncover the genetic basis of host response to the PRRS virus.

A nursery pig infection model of 200 pigs for each of the eight trials was completed at the KSU biosecure animal facility using high-health pigs donated by commercial breeding stock companies. Blood was collected at 10 time points for a total of 20,000 serum samples per trial and 160,000 serum samples collected in all. Researchers measured viral levels, immune proteins, antibodies and cytokines (interferons, interleukins), plus a similar set of blood samples collected for analysis of gene expression.

An analysis of the pig samples indicates that all pigs were susceptible to PRRS virus infection. However, some pigs were resistant to infection, cleared the infection rapidly, and produced nearly normal weight gain while showing no reappearance of virus.

Other pigs in the study were more susceptible, carried persistent infection and had low or no weight gain. Unfortunately, those resistant pigs that produced close-to-normal weight gain also retained higher viral levels.

Preliminary genome-wide association analysis has begun to identify chromosomal regions that account for these different PRRS response phenotypes.

All consortium data is being stored in the secure, password-protected database at ISU,

Researchers: Joan Lunney, Animal Parasitic Diseases Laboratory, ARS, USDA, Beltsville, MD; Bob Rowland, Kansas State University; James Reecy, Iowa State University. For more information, contact Lunney by phone (301) 504-9368, fax (301) 504-5306 or e-mail; contact Rowland by phone (785) 532-4631, fax (785) 532-4481 or e-mail; contact Reecy by phone (515) 294-9269, fax (515) 294-2401 or e-mail