Gene Edited Pig Offers Hope Against Costly Hog Disease

Porcine Reproductive and Respiratory Syndrome, or PRRS, was first identified 37 years ago in the United States. It showed up sporadically in 1987, causing respiratory disease in hogs as well as inducing sows to abort their litters.

The illness, triggered by a virus that can mutate rapidly, has stubbornly stuck around since, overcoming management attempts and spreading globally.

Dr. Derald Holtkamp, Iowa State University College of Veterinary Medicine: “You go through these cycles of, you know, you are happy that you think you got some solutions and then you realize, nope, it’s found a way to outsmart us again.”

Iowa State University veterinary medicine professor Dr. Derald Holtkamp, along with a peer, released a new study this summer that demonstrates the illness’ increasing cost to farmers through lost animals, lower fertility and reduced weight gain.

Since an earlier study began in 2000 and this new one was completed in 2020, the economic impact of PRRS grew from $560 million annually to $1.2 billion, an increase of 114 percent. Even after adjusting for inflation and a larger U.S. herd, the annual losses as of 2020 still exceeded $1 billion a year.

Dr. Derald Holtkamp, Iowa State University College of Veterinary Medicine: “I thought it was going to go up but I didn’t think it was going to go up by that much…As I do with all of these types of studies, I usually go to my veterinary friends and I say, ‘Is this what you are seeing in the field? Does this make sense to you?’ And without fail, they said, ‘Yeah that looks right to us.’”

The study showed hog mortality rates up to 5.3 percent higher than for those without PRRS. Several vaccines are available but Holtkamp says they seem to be less effective when new versions of the virus crop up. There is no evidence of the PRRS virus affecting humans.

Dr. Derald Holtkamp, Iowa State University College of Veterinary Medicine: “They’re just extremely severe viruses. That when they got into a herd, the virus replication was just tremendous. More than we’ve ever seen. And the disease caused by those isolates was very, very severe and so, in many cases, the best option was to simply de-populate the herd and start over.” 

Iowa pork producer Gene Gourley says PRRS is the reason his family is stepping away from raising sows.

Gene Gourley, Gourley Brothers - Webster City, Iowa: “Our father started in ‘56 with farrowing three bred animals from a neighbor. And today we are - 65 years later basically - are shutting down our only…sow facility we had left, due to PRRS…otherwise we would still be farrowing sows today.” 

There is a potential solution on the horizon: a genetically edited pig that the federal government is in the process of considering for commercial release.

Through gene editing, the Tennessee-based Pig Improvement Company, or PIC, along with the University of Missouri and The Roslin Institute, have found a way to knock out a specific portion of a protein in the genetic code of hogs.

Banks Baker, Global Director of Product Sustainability, PIC: “We can utilize gene editing and Crispr technology to go in and edit a specific portion of the protein. And once we have that edit, then it makes the pigs completely resilient to the PRRS  virus.”

Baker said the work on licensing and regulatory approval have been slow-going but they are hopeful the FDA will approve their PRRS-resistant pig by late 2025. This PRRS-resistant pig would join a short list of genetically altered food animals already approved for human consumption. 

In December 2023, the FDA, for the first time, approved a gene-editing therapy for treating humans, in this case, those suffering from sickle cell disease.

Banks Baker, Global Director of Product Sustainability, PIC: “The benefits of this technology are extremely significant, and we’re excited to be among one of the first companies that are bringing something like this to the market on a commercial population. Because this is likely how we are going to end up solving a lot of the devastating animal diseases that we deal with on a production basis day-to-day.” 

Although the first PRRS-resistant pigs are already being bred in carefully controlled facilities, they are not allowed to leave these buildings and can not be harvested for their meat. Even if the FDA gives the green light, these pigs will presumably be too valuable for their recessive genetic trait to land on anyone’s plate anytime soon.

Banks Baker, Global Director of Product Sustainability, PIC: “This isn’t like a light switch where all of a sudden we get approval, and these pigs will be available for everybody to utilize. We think about it in terms of more of a dimmer switch so it’s going to take time to breed this trait within those commercial populations and get full coverage.”

Brazil and Columbia have already determined that even though the pigs are genetically edited, because they don’t have additional DNA from other animals or plants, they can be treated as conventional products. However, PIC is moving cautiously.

Banks Baker, Global Director of Product Sustainability, PIC: “We understand that the global pork market is global in nature and so we want to make sure that we have the appropriate level of approvals across all of the importing and exporting countries.”

PIC, and parent company Genus, are seeking approval from other countries including Canada, Mexico and Japan.

Baker says they don’t want cost to be a barrier for farmers as they hope to bring the genetics to all producers battling PRRS, perhaps three to five years after approval.

The Gourley Brothers farm would have tried to move toward a PRRS-resistant pig if the option had arrived time. But, instead, they are cutting their losses and focusing only on finishing hogs.

Gene Gourley, Gourley Brothers - Webster City, Iowa: “It’s hard on your heart strings because you’ve had those animals all your life and you’ve cared for them and you’ve had mothers you’ve been able to tend their litters and take care of them, and see that production from start to finish. And you had the pride of your dad starting it and raising us kids and that’s how we’ve grown our farm operation …. It’s just, it’s not sustainable to keep doing what we’re doing.”

By Colleen Bradford Krantz, colleen.krantz@iowapbs.org