The increasing availability of genomic tools allows for a much more detailed analysis of genetic influences on a pigs response to a disease challenge. The most difficult part of this research is collecting disease “phenotypes” which are generally associated with responses of pigs that are undergoing a disease challenge.

Fortunately a few groups have collaborated to fund and supply pigs and facilities where these phenotypes can be collected. Early research has pointed to some aspect of genetic control to a pig’s response to a disease challenge. The issue has been to refine the understanding of genetic control and then to determine how best to implement selection.

At the World Congress of Genetics Applied to Livestock Production meeting in August 2014 and the North American PRRS Symposium held in December 2014, the results of initial and continuing research were discussed.

Based on the number of papers presented there has been a significant increase in activity associated with the genetic component of swine disease. One paper by Serão et al. (2014) validated that the phenotype resulting from a PRRS ELISA test, known as the sample to positive ratio (S/P), was under significant genetic control.

The S/P is a measure of the pig’s response to a PRRS virus. This has now been demonstrated in reproductive sows undergoing a PRRS outbreak (Serão et al. 2014a) and also in high-health commercial gilts during acclimation to low-level health farms (Serão et al. 2014b).

In both studies, genomic regions on chromosome 7 were identified as having significant impact on the pig’s response. These studies demonstrated that antibody response during a PRRS outbreak can be predicted using genetic markers on chromosome 7 and that results are consistent across different Landrace-Yorkshire populations.

Additionally, a paper presented by Hess et al. (2014) at the North American PRRS Symposium extended the work of Boddicker et al. (2012) to a second PRRS virus isolate. Boddicker et al. (2012) had shown that a region on chromosome 4 (WUR) significantly reduced viral load and increased weight gain in the initial 21 days after weaning.

Hess et al. (2014) used a different PRRS virus isolate under the same testing protocol and procedures and demonstrated that there was a significant reduction in viral load of pigs having the favorable WUR genotype for both PRRS virus isolates. These results suggest that selection for the favourable WUR will result in reduced viral load in pigs undergoing a PRRS challenge of either virus isolate.

Clearly genetic contributions to the pig’s ability to mount an immune response to viral challenges has been demonstrated with resultant impacts on growth and some reproductive traits. The potential to improve the disease response of individual pigs by genetic selection is getting closer to reality.

Geneticists need to determine the potential economic impact of such selection on other economically important traits. It is exciting to think about a day when effective disease selection is routinely incorporated into genetic selection indexes.

Genesus, as part of its continual R&D investment has been a significant contributor to these research projects in addition to an internal research effort.