USDA Agricultural Research Service and University of Nebraska scientists are part of a team that has found a vital clue for battling porcine reproductive and respiratory syndrome which costs U.S. swine producers about $560 million annually.

The scientists evaluated two lines of swine for genetic resistance to PRRS. The Nebraska Index line (I) was chosen because of its improved reproductive traits, and the Hampshire by Duroc cross (HD) was selected for its high growth rates.

All pigs in both groups became infected after exposure to PRRSV. However, I pigs generally recovered more quickly, maintained higher levels of weight gain during their illness and had lower body temperatures. In addition, tissue samples showed that virus levels cleared more quickly in PRRS-resistant I and HD pigs.

The scientists then looked at the tissue expression of 11 genes and one "housekeeping" gene involved in the immune response to PRRSV. Both I and HD swine showed significant activity in 11 of the 12 genes, but the type of activity differed between the two groups. High pre-infection blood levels of one protein, interleukin-8—IL8—was found to be significantly associated with PRRS-resistant pigs. Low levels of another protein, interferon-gamma—IFNG—in blood and in RNA samples was also correlated with PRRS resistance.

These findings support existing research that indicates animal breeds with high growth rates devote less energy to immune and disease traits. This information will facilitate work into developing genetic tools for increasing swine resistance to PRRSV. ARS is the USDA's chief scientific research agency.
Source: USDA Agricultural Research Service