GenomeAlberta reports that researchers in the United States recently discovered a genetic marker on chromosome four that affects, to a large extent, the viral load and growth rate of pigs infected by PRRS. Pigs generating more viruses also gain less weight, and vice versa. The research was partially funded by the PRRS Host Genetics Consortium, an international group studying the disease’s genetics.

“First of all, that’s an exciting result because we didn’t necessarily expect to be able to see such a big impact. Normally, in some of these traits, we expect to see lots of regions of the genome explaining a small amount of variation, and then you have to trap all of them. But in this case, there is…a loci explaining enough variation that it should be interesting to go after that region and select for animals that are less susceptible to PRRS,“ says Dr Graham Plastow, CEO of Livestock Gentec. Plastow is one of the researchers working on the Canadian component of the consortium research.

Different PRRS strains can be grouped into two genotypes - Type 1 and Type 2. However, within each genotype there are several subgroups, and variants within that subgroup, making PRRS one of the most genetically diverse viruses. The research to date has focused on a single strain of PRRS that was well-suited to the experiments, so the next step will examine how this genomic region reacts to different strains.

“Is this same region going to behave in the same way with a different strain? Because if it isn’t then it will have limited impact for the industry because PRRS changes quite readily. It would be an arms race and we’d start to select for pigs with this region, but actually if they didn’t affect the other virus, we might not have any economic impact for the producer,“ says Dr Plastow.

Canadian researchers are looking at how chromosome four’s genetic marker affects the pig’s response to reproductive PRRS. Scientists are now running a pilot at the University of Saskatchewan to see which of four strains will work best for the reproductive PRRS experiments.

“Obviously if there was one that was so aggressive that all of the pigs aborted, we’d have less information than if we have a range of outcomes. To get the best research we need to have a balance between the aggressiveness of the virus and variation,“ Dr Plastow says.

Each year PRRS costs the US pork industry $664 million, according to Pork Checkoff. Together, circovirus and PRRS cost the Canadian industry $100 million every year. Such losses add up to a real need for research that will help the hog industry battle the disease.

Further Reading

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