Exterior of a filtered hog barn National Pork Board

Air filtration for swine herds: A historical perspective

PRRS has been a game changer in the swine industry, and filtration of hog barns has made great strides in reduction of the the spread of the air-borne strains of the virus.

Porcine reproductive and respiratory syndrome has been a game-changer in the U.S. swine industry. Having first been described in the United States in 1987-88 in North Carolina, Iowa and Minnesota, the economic impact to producers has been compounded most recently attributed to $580.62 million each year.

Though a lot has been learned about PRRS, control of the virus is far from accomplished. Great strides have been made, with the recent technological advancements in the area of gene editing, presenting the potential to create a pig immune to PRRS. Progress has also been made with companies releasing live-virus vaccines that help herds build immunity. But several years ago, one of the biggest challenges was reducing the risk of airborne spread.

National Hog Farmer/Kevin Schulz

Scott Dee, veterinarian with Pipestone Veterinary Services and the director of Pipestone Applied Research

Filtration comes to America
Scott Dee, veterinarian with the Pipestone Veterinary Services and the director of Pipestone Applied Research, became intrigued with potential ways to stop farms from becoming infected with PRRS while he was a practitioner in Morris, Minn., from 1987-99, and while he was a professor at the University of Minnesota College of Veterinary Medicine. His research there focused on the transmission and biosecurity of PRRSV for a 12-year period.

In 2003, while he was still at the U of Minn., a new PRRSV strain — 184 — surfaced causing high mortalities in sows and “seemed to just jump from place to place”. Follow-up work by Dee and one of his students, Jenny Cho demonstrated that this virus had a great ability to replicate inside a pig and exhaling aerosols containing a quantity of virus that was significantly higher than from pigs infected with some of the older PRRSV strains.

Based on this information, in October of 2004, Dee’s intrigue with aerosol transmission of PRRSV took him to Brittany, France, where he had veterinarian friends who had started filtering hog farms. “Now that I knew air-borne risk was real, I wanted to learn what they were up to.”

The Brittany area of France, Dee says, is like the “Iowa of France” with hog farms very close together, though not very large. Filtered breeding stock farms, having been established for one to two years by the time Dee visited, were located right in the middle of all of this hog congestion, “and they had good clinical findings that filtration seemed to prevent infection; however, there was no hard data to support this observation.”

The French barns that Dee visited were all positive-pressure. The French had also employed the use of high-efficiency particulate air filters, which Dee calls the most efficient, but also most expensive, means of filtration. HEPA filters are about 99% efficient at particle removal, and are often found in hospitals and other medical facilities.

“I remember riding home on the airplane, thinking that air filtration is the answer, but we have to make it work for the U.S. national herd. We have to do it cheaper, and we have to do it with negative pressure because that’s the way all our buildings were set up.”

Proving the concept
Dee took his excitement from that October 2004 trip, and turned it into performing proof of concept research work at the University of Minnesota in 2004-05. Starting with rudimentary filter chambers, Dee set out to see if he could prevent infection, “and it worked.” Working off the French model, Dee worked with HEPA filters, and then started showing that less efficient, lower cost filters also worked very well.

Having shown success, Dee started getting the word out by publishing his results and doing presentations at industry conferences, and “people started to take notice and listen.”

As chance would have it, Dee found himself on a National Pork Board speaking circuit with Steve Pohl, South Dakota State University professor of Agricultural and Biosystems Engineering, who was presenting ventilation information, and “we started talking about how all this would work together,” Dee recalls. “So here we have a very talented engineer who can actually calculate the correct cfm and the airflow, measure the resistance and determine how many filters you’re going to need, how much inlet space you’ll need to make sure the pigs would get enough air. I could manage the virus, but we had to make sure the pigs could breathe. Steve deserves a great deal of credit for all that effort.”

The Pohl and Dee team were now looking for opportunities, and the first to come along was the Pipestone System boar stud in 2005. “Gordon Spronk (Pipestone System co-founder) was the real pioneer in putting air filtration into the real world,” Dee says, adding that the Pipestone boar stud was the first commercial success of a filtered barn.

The production region model
To further validate the process, in 2006, Dee developed and initiated a new project, funded by the National Pork Board, called the “production region model” that simulated a dense population project to mirror what was taking place across the Midwest countryside. “We set up four buildings, all close in proximity to one another. One facility contained 300 grow-finish pigs, the ‘source population’, and downwind from that we bought three small double-L nurseries, some filtered, and some not.” The grow-finish pigs were infected with the 184 strain and Mycoplasma hyopneumoniae in the “source” population. Downwind were the nursery barns housing negative pigs, and every two weeks new pigs were brought into the source herd to “keep the infection active.”

Using this approach, airborne pathogens were detected in exhausted air from the source population, across the landscape and right outside the downwind facilities. “Most importantly, we demonstrated the ability to keep the filtered barn free of infection, while the unfiltered barn became infected at a 30% infection rate.” To eliminate the doubt of PRRS virus and M hyo coming into the barns through other means than aerosol, Dee and his team were diligent in swabbing people and supplies coming in, testing insects, swabbing trailers and collecting air coming in to the barn. The leader of the team, Andrea Pitkin, now with PIC, ran this project as part of her master’s thesis. “The production region model was the first attempt to show on a day-to-day basis for an entire year if it was possible to keep a group of negative pigs free under a filtered condition. Then in a nonfiltered system, how often would those pigs become infected,” Dee says. As part of the project, researchers gathered any and all possible weather data using an on-site weather station — humidity, temperature, barometric pressure, wind speed and direction — “and we put together a set a meteorological guidelines as to what is high-risk and what is low-risk for PRRS virus aerosol infection.”

Dee says Pitkin deserves a lot of credit for what at the time was the most impactful study to show the efficacy of filtration and the risks of spread is various conditions. “There had never been a study of this type conducted before. Basically we modeled what I saw in Brittany, France, in 2004.” Another one of Dee’s students, Satoshi Otake, came back to the University of Minnesota and continued Pitkin’s production regional model for his post-doctorate work, adding three years to the project. Filter technology was evolving, and Dee and Otake looked at various types of filters and media, “and every filtered facility remained free for the entire four years,” Dee says. “At the end of the four years not one of the filtered barns had become infected, while the non-filtered control populations became infected 30% of the time.”

Taking it to the real world
Following sharing of the results of this study at the 2007 Leman Swine Conference, Spronk once again stepped forward with the vision of filtering a large commercial sow farm, which had never been done. The sow farm that Spronk was suggesting had 3,000 sows located in the heart of pig production in southern Minnesota, and it broke at least once every year with PRRS. “They basically would just figure it into the cash flow,” Dee says, “It was that regular occurrence, and always a new virus, never the old one.”

Dee says Spronk issued a challenge of taking the filtration practice that appeared to work on a small scale, both in the boar stud and the production region model, and take it into the “real world.”

“I said definitely, but we have got to bring Steve Pohl in,” Dee says, “which we did and away we went.”

The barn stayed PRRS-free for the first year, which it never had done before. Next for Dee was to see if this one barn’s success could be replicated on a grander scale, across multiple units over time. “I had been at the University for over 10 years and really enjoyed the time; however, I was looking for something bigger, I wanted to make a significant impact in the industry. You know, a published paper is nice, but if it’s a dusty old journal that sits on a shelf and no one ever looks at it, it doesn’t have much value,” Dee says. So, in 2011, he went to Luke Minion (Pipestone System chief executive officer) and Spronk to ask for a job. “I simply wanted to see if what we had developed at the U of M would work on a large scale. Based on the leadership of Pipestone in the science and application of air filtration, it made sense to get involved.”

Lessons learned
With Dee coming to Pipestone, this was the first leap of filtration into commercial sow farms and with it came many challenges. “We had to change behavior at the farm level. For example, you can’t just open the door anymore. How do you move pigs out without letting potentially contaminated air in?”

A lot of training and education of farm employees took place. “Gordon had the idea of having employees take regular biosecurity-based quizzes, using real-world scenarios.” Dee says the employees “really caught on fast, because they were all getting sick of having PRRS, and they got really excited when they started to see the infections stop.”

Unfortunately, “success was our worst enemy,” Dee says, “because people started to get lax on the biosecurity once PRRS cases started to drop. Therefore, we had to focus even harder and pay attention to the protocols.” Dee predicts that some farms do not adopt filtration systems “because deep down they know they cannot execute the biosecurity details necessary to make a filtration system work optimally.”

Another learning curve was the issue of filter longevity. Though they sought out the best filters to efficiently keep PRRS and other particles out of the sow farms, Dee says they learned that filters do not stand up forever. “We didn’t know that at first, but we learned that independent of media type (fiberglass or polypropylene), all filters lose performance over time. In addition, we learned that the adhesives are also affected by the aging process and would separate from the media and the frame causing bypass of non-filtered air.” The aging process of the filter wasn’t understood when Dee started his research, but it became a real concern when a system the size of Pipestone puts in as many filters as they do. “When you’re putting thousands (of filters) in a facility, the cost gets pretty high, so we want to stretch that investment out as long as we can.”

Though trying to stretch the filter’s life makes economic sense, that becomes difficult when filters meet the environment of a hog barn — fluctuating temperatures, high moisture and high dust. “Moisture is the Achilles heel for filters,” Dee says.

As Pipestone gained more experience with filters, they gave feedback to the manufacturers. “Some were responsive and some were not. Those that were willing to work with us to get better clearly got our loyalty. After 10-plus years of filtering and thousands of filters tested we have learned that all filters are not created equal and there are definitely differences in quality and lifespan.” Pipestone Veterinary Services has helped many producers with their preventative plans.

“We also learned that we had to devise ways to protect against backdrafts of fans and air leaks that are apparent in both positive and negative pressure facilities. … There was a lot of learning we had to do after the ‘honeymoon’ period. One of the lessons was this is not a perfect process. The filter system is a dynamic entity, it a living thing, it’s changing and aging over time, but when used right it does work very well.”

Before you even think of filtering a barn, Dee recommends that farms have a comprehensive biosecurity plan in place, involving personnel and supply entry, pig movement, quarantine and testing and transport sanitation programs. “You need to have all that in place before even thinking about putting in a filtration system. If you don’t have all the biosecurity bases covered, the filters will fail.” Dee says it’s also important to evaluate filters on a regular basis to monitor their performance, looking at air flow and fractional efficiency, as well as their structural integrity. Filters from Pipestone barns are sent to LMS Technologies in Minneapolis, a third-party lab to test the filters. The third-party lab provides transparency, as well as offering unique facilities for additional testing. “At LMS, we’ll expose filters to repeated wet/dry cycles, thermocycles (freezing conditions versus hot conditions) and extreme pressure secondary to heavy dust loading. We want to model three to four years of time in the swine environment to see what these filters have to deal with on a daily basis.”

Any new sow farm, which includes the GDU, built in the Pipestone System is built with filtration, and currently 44 of 60 sow farms in the system are filtered accounting for about 150,000 of the system’s 225,000 sows. “We have some barns that have 3,000 days of filtration with no breaks, and with that track record, people are more accepting of the technology.” He estimates close to 1 million sows in the United States live in the benefit of filtered barns.

At this time, the current Pipestone System filtered barns remain negative-pressured filtration barns. Though the debate between negative and positive filtered barns continues, Dee doesn’t care what producers use. “We’ve been on a steep learning curve with negative pressure and we think we’ve got a pretty good system now. We love the concept of positive pressure, and we want to continue to learn, but with that comes diligence on protocols and backdraft/air leak prevention.”

Dee says the Pipestone System, and the U.S. hog industry as a whole, needs to work to further lower PRRS break rates, with less than 10% being an acceptable rate. He is confident that filtered barns — positive or negative — are the key to achieving that goal.

“Any filtered barn that prevents disease spread is good for everyone,” Dee says. “It’s fun to help people reduce their risk of PRRSV infections, we have worked with many systems across the country and really enjoy that. I took on the challenge of air filtration PRRSV to make a difference. It has been very successful and I am very proud to have been involved from the beginning.”

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