The U.S. swine industry may have "learned to live" with domestic diseases in the wean-to-market phase of production, however Kate Dion says preventing lateral introductions could be key to preparing for foreign animal diseases as well as protecting the U.S. sow herd.

"We're missing some opportunity there and the big one is that we need to protect our sow farms," Dion says. "We've invested a lot of money in the facilities and those animals, and we can drag diseases back, and the more diseases that we have prevalent in our wean-to-market population causes risk for our sow farms."

Dion, a veterinarian with Hanor Company who is also pursuing a PhD in population sciences in animal health at Iowa State University College of Veterinary Medicine, shared her latest research with lateral disease introductions and her experience in wean-to-market biosecurity during the 2022 Iowa Swine Day.

According to data from the Swine Disease Reporting System, over the last two years increases in the number of sow farms positive for porcine reproductive and respiratory syndrome across the United States has actually been preceded by an increase in positives in the growing pig population.

"I think we could probably say is this a chicken or an egg thing, but in likelihood it's probably that we're spreading PRRSV in those populations and putting those farms at risk, that are either in similar areas or tracking it back to the sow farm," Dion says.

While biosecurity hasn't always been a focal point for the wean-to-market phase, the cost of a disease outbreak is significant. Dion references the 2013 Holtkamp cost analysis of a PRRS outbreak in the grow-finish phase, showing a $2.29 per head cost due to increased mortality and slower growth. She also points to the 2020 Wedel study that found if 23% of growing pigs in a production system became positive with coronaviruses, in 14 months it would cause a $1.6 million loss to that system.

The economic impact is even more significant if pigs become positive for both diseases during the growing phase, no matter if PRRS or coronavirus came first. Henness (2018) found a $7.08 cost/pig compared to pigs that remained negative for both pathogens.

"There is a lot of opportunity we could get back if we could limit some of these pathogen introductions, but we have a lot of challenges about how we choose to raise our wean-to-market pigs in the United States," Dion says.

Those challenges include having farms in high density locations and an infrastructure of industry reliance on contracts.

"We can spread out that cost of production, allow more people to be involved, but that means that generally a lot of our inputs and facilities are contracted out, and that might be the facilities, the labor, the feed, maintenance, transportation and even handling manure. And then maybe further from there, those contractors may subcontract out some of that labor," Dion says. "Ultimately what really happens is that we end up with a lot of our farms, that although they may not be with the same producer or the same production system, they're very tied together because so much contract labor in facilities is occurring."

Growing pig biosecurity study
Dion is currently conducting a growing pig biosecurity study with 75 groups of pigs in Northwest Iowa. The pigs started off as negative for PRRS, porcine epidemic diarrhea, porcine deltacoronavirus and transmissible gastroenteritis virus at placement from the sow farm and were not vaccinated for PRRS. Oral fluids and biosecurity characteristics and events were collected every two weeks.

TGEV was not detected in any of the farms. Eleven of the groups became positive for PEDV, 19 for PDCoV and 73 for PRRSV.

"So, what this really means for us, is we have a lot of lateral disease transmission occurring, and so while that can be really frustrating for me as a veterinarian, wishing that we weren't having all of our pigs having a lateral introduction of PRRS … what that really means is we have to flip that on its head," Dion says. "It means we have a lot of opportunity, a lot of places that we can improve, and then hopefully we can eventually figure out how we could reduce these introductions and recoup some of that cost that occurs to our producers when they get a lateral infection."

Diving into the diagnostics a little bit more, Dion points to some distinctive patterns, with PEDV introductions occurring in the nursery phase and a couple during the late finishing phase. PDCoV was similar, while PRRSV looked quite a bit different, with many introductions in the early finisher phase.

Another noteworthy observation was the larger farms in the study were more likely to become positive for all three diseases compared to the smaller herd size farms.

"As you can imagine with a larger herd size, there's just more events that are going to have to happen. We have to get more feed in. We have to have more loads of animals in, more loads of animals out. They have to probably have a little bit more labor potentially to run those facilities," Dion says. "We have to enter supplies more frequently, so there's just going to be a trend towards more events occurring on a larger herd size that may make it more susceptible for a disease introduction."

One "event" Dion says grow-finish facilities cannot dismiss in disease introduction is the role of the caretaker.

"There's been very early work with PRRS that if you just wash your hands and change your boots and your clothing, that's good enough to prevent moving PRRS into pigs if you're contaminated," Dion says. "But yet we see a lot of introductions and we tend to have in the wean-to-market phase, a lot of folks that may chore more than one barn – management, veterinarians, visitors, we go farm to farm, and that's quite different than most of our sow farms."

To understand if the movement of caretakers from one premise to another impacted the spread of the four diseases during the nursery phase of production, Dion decided to study a subset of the farms within the 75 groups.

During the nursery phase employees use a program called Timesheet Mobile (Freedom Telecare, Westborough, MA) to clock in and clock out. The system is geofenced to a farm location, so caregiver visits to the site could be identified as well as other site visits prior to the study site for 72 hours.

Using diagnostics in the system, as well as sow farm diagnostics, Dion assigned all of the sites visited a disease status for the groups and for the sites of pigs that they visited prior to coming to the farm. This allowed them to then summarize the number of positive versus negative sites that they visited for each disease.

Sixty-three groups were eligible for this portion of the study. There were no TGE detections, eight of those nurseries became positive for PED, 12 for PDCoV and six for PRRS.

While the number of visits between farms started to add up over time, Dion says ultimately neither employee visits nor the ratio of the number of visits from positive premises over the total number of visits were statistically significant in the logistic regression for any pathogen.

"This may suggest that more frequent caretaker visits or visiting a higher ratio of positive sites is not associated with introduction of virus into these pigs that were previously negative," Dion says.

She also notes that three days out might be too far out to be evaluated and further research may need to examine one to two days prior to site visits. Also, risk may have been mitigated by caretakers following entry procedures, she says.

Marathon, not a sprint
The commercial production veterinarian says building an on-farm biosecurity culture takes time and may even be a new concept for many wean-to-finish farms. She suggests implementing the following protocols:

The biggest thing in implementing better biosecurity on wean-to-finish is to just get started somewhere, Dion says.

"We don't have to go out and do all the facility improvements, but maybe if we're using something like rendering, we want to make sure that we address that the boots that we're wearing in the barn don't go out to the rendering box, that we may not drag the stuff into the barn that might have come from the rendering truck," Dion says.

Finally, she says small progress is still progress.

"It's a marathon. It's not a sprint," Dion says. "We're not going to get through this race really quickly. It's not going to end. We're going to have to keep going and trying to maintain and improve biosecurity."

The 11th annual Iowa Swine Day was held June 30 at Iowa State University. More information on the conference and sponsors can be found here. Videos and presentation files for many of the plenary and concurrent sessions can be found on the Iowa Pork Industry Center YouTube channel.