Reducing PRRS outbreaks by using air filtration: What you need to know

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.”



Top-notch gilt management requires attention to details

The basics of managing gilts for optimum pig production and longevity are well known. But successfully applying them requires meticulous attention to details, according to Jake Schwartz, DVM, Swine Vet Center.

“The best farms really embrace the details and make sure they’re executed 7 days a week,” Schwartz said. “That’s the difference between average farms and great farms.”

There are some basic rules he recommends for ensuring gilts realize their full genetic potential and become prolific members of the sow herd.

Disease management

The first is managing disease threats like porcine reproductive and respiratory syndrome (PRRS), which can derail gilt performance. Schwartz suggests either keeping PRRS out of the herd or finding an appropriate way to handle it in a herd.

“[If] PRRS management strategy involves vaccine or serum exposure, the timing of those two events is important,” he said. “Do exposure early in the gilt’s life so when she farrows the first time, she’s not giving birth to PRRS-positive pigs.”

He also recommends avoiding PRRS exposure around time of breeding or right after breeding to prevent reproductive issues like mummies and abortions.

Parvovirus type 1 also causes reproductive issues with gilts, including increased rate of mummies, especially when they’re exposed for the first time post-breeding. All gilts should be vaccinated pre-breeding. If there is an elevated rate of mummies, there are some creative ways to get parvo exposure pre-breeding and minimize its impact.

No breeding on first heat

One breeding rule tops the list of production techniques for optimum gilt management. “It’s been well documented that when we breed an animal on her first estrus, we give up total born and farrowing rate,” Schwartz said. “Proper gilt management includes heat-no-servicing and breeding on a second or third heat.”

This rule is in place because a gilt’s uterus is still developing during first estrus and not quite able to handle a large litter, he explained.

Also remember not to equate gilt age with sexual maturity. “Some animals will cycle for the first time when they are 24 or 25 weeks of age. Others will cycle for the first time when they are 30 or 31 weeks of age,” he said. “It’s kind of a bell curve.”

Acclimate gilts early

Another technique for good gilt development is making sure nothing occurs to throw a gilt off feed in the 14 days prior to breeding. This means vaccinations should be completed and the gilts moved to their stalls at least 14 days before they are bred, Schwartz explained.

“Both of those things will, in some animals, throw them off feed around the time of breeding,” he said. “Then in subsequent farrowings, those gilts will have less pigs.”

Early estrus equals longevity

Time of puberty can be a trait used for gilt selection because gilts coming into heat early usually are the most prolific in the herd.

“When an animal comes into heat early or is one of the first third or half…we know those gilts tend to be more long-term, prolific members of the herd versus a gilt that first comes into heat at 30+ weeks for the first time,” Schwartz said. “Those gilts tend to be more short-term members of the herd and have lagging total born and farrow rate.”

The ideal gilt management program would select females that cycle by 30 or 31 weeks of age and younger. “In a perfect world, that’s what you would do,” he explained. “But unfortunately, given the constraints of some of the system’s farms, that’s often not the case.”