Jeff Feder, DVM, with Swine Vet Center (SVC), has spent 15 years fine-tuning filtration systems in client hog barns. Today, Feder has records to prove air filtration does reduce outbreaks of disease like porcine reproductive and respiratory syndrome (PRRS).

Looking back over records from 85 farms with filtration, he found these farms prior to filtration were breaking with PRRS over three times more frequently than with filtration.

“Many of the early farms were located in very pig-dense areas and, as a result, were having more breaks with PRRS and other respiratory pathogens than we would like,” reported Feder who works from SVC’s clinic in St. Peter, Minnesota.

“We looked at PRRS break rates to understand if we were moving the needle and changing the number of PRRS breaks…We were able to cut those breaks by a third.”

Explaining filters
Air filtration systems are expensive. Feder said the early ones cost $150 per sow space, but today are at least three times that amount. They can be installed on new and existing facilities.

The filters are key to keeping pathogens out of hog buildings, and Feder has learned which ones are best. Fiberglass filters retain efficiency much longer than synthetic filters. He took used filters of both types out of hog buildings to be tested for filtering efficiency at certified labs.

“Often clients budgeted for those filters to last 2 to 3 years,” he said. “What we found was…the fiberglass filters will maintain their efficiency for a long time.”

Feder also recommends using fiberglass filters with a minimum efficiency reporting value (MERV) of 15 or 16. This means 92% to 95% of the very smallest particles will be removed by the filter.
“Typically, in a filtration system in a pig barn, you have what I call the main filter or end filter, and most commonly those have MERV 14, MERV 15 or MERV 16,” he explained. “Then they have a type of prefilter like the furnace filter in your home. The goal of the prefilter is to take out the large dust particles so those particles don’t plug up our expensive end filters.”

Impact on existing ventilation
Most of the filtration systems used by SVC clients are retrofits put on existing ventilation systems in hog barns.

“One common scenario in the top-down ventilation system is to simply install the filters over the top of the ceiling inlets, and that is your point of filtration,” Feder explained. “In tunnel-ventilated barns, you build filter banks in front of the cool cells before air enters through the end of the barn.”

Other modifications may be needed to accommodate air filtration. Often existing fans don’t move as much air as before the filters were added due to higher static pressure. Keeping fan shutters and blades clean may be enough to increase their efficiency. Otherwise extra fans can be installed to boost airflow.

When cool cells are involved, Feder recommends making sure they work correctly and are on a timer. Airflow filtration is reduced when water is running through the cell pads.

Negative versus positive pressure
Most existing hog facilities are negative-pressure ventilation systems, according to Feder. Some new buildings with filtration use positive-pressure systems.

“The benefit of the positive-pressure system, at least in a filtration scenario, would be if there are any leaks in the barn, those leaks are getting pushed out so it’s filtered air being pushed out,” he explained. “On the flipside in negative-pressure systems, if there are leaks, it’s unfiltered air leaking into the barn and that’s not a good thing.”

While the positive-pressure system sounds better, he cautions that ventilation rates run higher which can lead to higher LP usage rates in colder climates. In addition, there’s more potentially contaminated air being pushed into the barn, which could be a problem.

“Negative-pressure systems run at much lower ventilation rates in the winter, but we do have to worry about leaks,” Feder said. “We’ve spent a lot of time over the years figuring out how to build them tighter with different construction ideas using foam and caulk…to get these barns very tight.”

Air filtration works
“I completely believe in filtration and think that it’s a good tool to use, especially if you’re in a pig-dense area,” Feder said. “I would just caution, though, that it’s like any other tool that has to be managed.”

“Along with filtration come some additional things that need to happen. Make sure we’re monitoring the performance of the filters, looking for air leaks on farms and we do all the other things for biosecurity correctly as well.”