A consortium of scientists from around the country has discovered a genetic marker in pigs that identifies whether or not the animal has a reduced susceptibility to porcine reproductive and respiratory syndrome (PRRS).

The researchers found a genetic marker, called a quantitative trait locus, on swine chromosome 4 that is associated with resistance to PRRS virus infection. The finding at this location is particularly important as it also is associated with improved growth of pigs that are infected with the PRRS virus. The results show a positive effect for PRRS resistance and higher weight gain, says Joan Lunney, a research scientist at the USDA's Agricultural Research Service (ARS) in Beltsville, Md.

According to Chris Hostetler, NPB's director of animal science, the identification of the marker gene that’s 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.

"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 notes.

The research team that led to this marker discovery includes scientists at USDA's Agricultural Research Service (ARS), Kansas State University and Iowa State University. The researchers continue to be funded by the PRRS Host Genetics Consortium, a nationwide effort originally funded by NPB; the Coordinated Agricultural Project program; the National Institute of Food and Agriculture and the U.S. Swine Genome Coordinator for the National Animal Genome Research Program.

To obtain the data necessary for the marker research, researchers collected blood and tissue samples, along with weight-gain data, from 2,000 pigs at biosecure facilities at Kansas State University. From there, ARS researchers performed genomic work at the facilities in Beltsville. Finally, Iowa State University researchers 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.

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

The U.S. pork industry has dealt with PRRS for more than 20 years and is it the industry’s most costly disease. In late 2011, Iowa State University researchers updated economic calculations and found that PRRS costs the U.S. pork industry an estimated $664 million annually. While PRRS does not present a concern for people or the end product, it does impact pigs of all ages from a production and growth standpoint.

"PRRS is one of the industry's top ongoing issues, so this research discovery is a major step in the right direction," says Lisa Becton, NPB's director of swine health and information. The particular finding builds off of work that originally received National Pork Checkoff funding.  

"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," Becton adds.  

More on checkoff-funded PRRS research results are available here.

Source: National Pork Board