DES MOINES, Iowa – A consortium of US scientists has discovered a genetic marker in pigs that identifies whether or not a pig has a reduced susceptibility to porcine reproductive and respiratory syndrome (PRRS). This disease annually costs the US pork industry approximately $664 million.

A genetic marker called quantitative trait locus was found by researchers on swine chromosome 4 that is associated with resistance to PRRS virus infection. This is especially important as this location also is associated with improved growth of pigs that are infected with the PRRS virus. She said results indicate a positive effect for PRRS resistance and higher weight gain, according to Joan Lunney, a research scientist at the USDA's Agricultural Research Service in Beltsville, Md.

"PRRS is one of the industry's top ongoing issues, so this research discovery is a major step in the right direction," said Lisa Becton, the Pork Checkoff's director of swine health and information. "Pork producers realize that supporting science-based research is not an overnight proposition. It's especially gratifying to achieve results like this and to envision how they can be implemented at the farm level."

The identification of the marker gene responsible for increasing resistance to PRRS will allow genetics companies to more easily place selection pressure on PRRS resistance, which in turn, could allow producers to introduce new "PRRS-resistant" lines into their herds, said Chris Hostetler, the Pork Checkoff's director of animal science. This could be one of the tools used to help eliminate PRRS, but more importantly, this work may provide the platform for finding similar marker genes responsible for conveying resistance to other economically devastating diseases, Hostetler said.

Scientists at USDA's ARS, Kansas State Univ. and Iowa State Univ. are included in the research team that led to this marker discovery. The researchers are being funded by the PRRS Host Genetics Consortium, a nationwide effort originally funded by the National Pork Board; the Coordinated Agricultural Project program; the National Institute of Food and Agriculture and the US Swine Genome Coordinator for the National Animal Genome Research Program.

Researchers collected blood and tissue samples, along with weight-gain data, from 2,000 pigs at biosecure facilities at Kansas State Univ. to obtain the data necessary for the marker research. ARS researchers then performed genomic work at the facilities in Beltsville. Researchers at Iowa State Univ. used the resulting genomic data to search the entire genome of all pigs from earlier trials done by the PRRS Host Genetics Consortium. They worked to identify chromosomal segments common to pigs that had lower levels of PRRS virus circulating in their blood and that grew faster after PRRS infection.

The next step is to pinpoint the gene and determine whether it shows the same effects for other strains of the PRRS virus now that scientists have found a chromosomal segment that can signify resistance to PRRS.