Common mistakes to avoid during PRRS elimination

Eliminating porcine reproductive and respiratory syndrome (PRRS) virus from a breeding herd is not a simple task, and no herd acts exactly like the next, according to Brad Leuwerke, DVM, with Swine Vet Center, St. Peter, Minnesota.

Looking back at years of PRRS elimination efforts, Leuwerke led a retrospective analysis of several breeding herds to determine why some were able to stay on course and achieve success while others were unsuccessful.

“We assessed several factors thought to influence a return to PRRS stability,” he said. “We found the season when the outbreak occurred, the virus strain causing the outbreak and the herd’s previous PRRS status all substantially affected the time necessary to eliminate the virus from the breeding herd.

“Largely, though, it feels like these factors are often out of our control.”

The review did highlight four factors producers can control that help drive successful virus elimination. “Failure to account for these aspects will extend the time necessary to achieve negative status,” Leuwerke said.

1) Avoid premature replacement entry

Producers must resist the urge to bring in extra replacement animals as a herd closure progresses. If replacements are brought in before the virus is eliminated, these animals will become infected and the closure time is drawn out.

“Instead, herds should ‘load up’ with replacements at the beginning of the closure to withstand the temptation to open up before the virus is eliminated,” Leuwerke said. “In addition, a reduction of culling, starting early in the closure, will also help in maintaining production goals without needing to open the herd.”

2) Set ‘day zero’ with an entire herd exposure

Start the PRRS elimination on a specified “day zero” using direct virus exposure of the entire herd.

“Infecting the entire population at one time allows for the shortest closure possible and is preferred over allowing the virus to naturally move through the population,” Leuwerke said.

This is especially important with newer, more virulent PRRS strains that look to have longer periods that animals shed virus.

3) Manage farrowing biosecurity

As a breeding herd nears the end of the closure, farrowing is the last place the virus can be found.

“The last animals to harbor and shed virus will do this through piglets, either born virus-positive or infected following birth,” Leuwerke explained. “Our biosecurity practices late in a closure influence the length of closure and, ultimately, if elimination is successful.”

At this stage, pigs should not be held back at weaning for more growth. “This is one of the worst things we can do in a sow herd working towards PRRS-negative status,” he said. It will extend the time of elimination.

Farrowing sanitation is very important, and poor practices can cause the elimination to fail. Leuwerke recommends all-out farrowing rooms at weaning so the rooms can be thoroughly washed, disinfected and dried. Common hallways also must be washed after all pig movements.

Good hygiene with processing tools must be practiced, too, to prevent the virus from spreading between litters.

4) Monitor herd status

“Newer monitoring strategies that allow us to test more animals have given us more confidence that a herd is truly negative before reopening to replacement animals,” Leuwerke said.

These new strategies include the use of processing fluids from many animals in the population.

“Before the use of processing fluids, we often would blood test 30 piglets each month,” he explained. “If we had 3 consecutive months negative, we called the herd negative. We likely missed virus using these testing procedures.”

Leuwerke admits PRRS eliminations are difficult. But good planning before a herd closure starts will help avoid common mistakes that lead to elimination failures.







New sow farm design minimizes disease transmission

A 2,200-sow, farrow-to-wean farm still under construction recently opened its doors for the public to see the latest technology in hog building design. More than 500 people registered to walk through the farm’s completed sow gestation and gilt development barns along with the unfinished farrowing barn.

The new Coleman Chops sow farm, being built by Brandon Romsdahl, is located near St. James, Minnesota. Swine Vet Center (SVC) helped owner Brent Coleman develop plans to better control disease and maintain a high-health status in the new facility. Brent, his father Dennis and family have farmed and raised hogs in this area for years. Brent will finish out all the hogs produced by the sow farm.

The new farm is equipped with several new features to help reduce disease entry into the farm, according to SVC’s Brad Leuwerke, DVM.

Filtered air

All air coming into the farm will be pulled through air fliters before entering the barn.

Brad Leuwerke, DVM, MS

“We know that using filters helps reduce the amount of virus that comes into a farm,” Leuwerke said. Many sow farms now use filters to help prevent the entry of diseases like porcine reproductive and respiratory syndrome (PRRS) into their herd.

Cement perimeter walls

The sow farm also has an outside concrete wall installed around the entire facility to reduce air leakage.

“A typical sow farm with wood and steel inherently has air leaks, that take a lot of time to continue to seal,” Leuwerke added. “The cement makes a tighter building and forces the air to go through the filters.”

The concrete walls are made with a plastic-forming system by Nuform. The plastic forms are snapped into place for the wall, rebar installed and cement poured into the forms. When hardened, the concrete wall has a smooth, white plastic exterior. The Nuform also has foam built in for better insulation and energy savings.

Biosecure entry and exit

When completed, the sow farm office will include a heated disinfection room to make sure all supplies brought into the farm will be pathogen-free. The room warms up to at least 90 degrees for a period of time to inactivate all pathogens. Everything going into the farm, will go through this room.

Other standard biosecurity measures are in place for workers and visitors entering the facility. Some of these measures include a pressurized entryway, an ultraviolet box to disinfect items necessary in the farm like employee lunches and electronics, and shower in with clothing changes.

In addition, pigs will exit the facilty through a pressurized loadout room that prevents the backdraft of unfiltered air when doors are open and trailers are being loaded.

Internal multiplication

The sow farm will develop its own gilts to reduce the risk of disease brought in by replacement gilts from another site.

“Brent and I discussed internal multiplication a lot,” Leuwerke said. “He had prior experience with this and we feel it’s a good way to reduce disease risk.

“A segment of his herd will be able to make the replacement animals. Those sows will farrow with other sows and their offspring we chose to keep will walk down the hallway and go into the gilt developer unit. They never leave the farm,” he explained.

If replacement gilts ever do need to be brought in, they will come in at 3 weeks of age and will go into a quarantine room. The animals will be tested and when cleared, will move into the main farm.

Small pen gestation

Gestating sows in the new farm start out in gestation stalls and move to small pens after reaching 50 days of pregnancy. Twelve similar sows will be kept in each pen together as a group for the duration of gestation

“We tend to find pens mixed with like size and age sows don’t fight as much,” Leuwerke said. “It doesn’t eliminate it, but it reduces it.”

Twelve stanchions in each pen for feeding and a simultaneous feed drop also help reduce aggression.

The first gilts were moved into the new facility shortly after the open house. The rest of the facility is expected to be completed in early 2020, in time for the first farrowings.

“Our hope is they can go for a long time without experiencing a major health challenge and be able to send pigs to the nursery that do well,” Leuwerke concluded.

Maintain sound on-farm biosecurity with PRRS ‘season’ approaching

By Brad Leuwerke, DVM, MS

As we creep closer to autumn’s weather change, crop harvest, manure pumping, etc., we also sneak closer to what has become a predictable rise in new cases of porcine reproductive and respiratory syndrome virus (PRRSv) across the country.

For 10 years now, the Dr. Bob Morrison Swine Health Monitoring Project has shown that the swine industry experiences an annual rise in PRRSv cases over an epidemic threshold in the October to November time frame. If history has anything to say, a similar trend should be expected this fall.

Knowing that one of the biggest drivers of profitability for swine producers is reducing nursery and finishing mortality and culls, those swine producers who are able to keep PRRSv out of their herds will have an economic advantage.

As fall arrives and the number of PRRSv cases begins to rise, swine veterinarians will start to get a sense of whether there are any new or more pathogenic “strains” that may become the new virus to be on the lookout for as an industry.

The last two to three years have given rise to PRRSv 1-7-4 and 1-3-4; both viruses caused severe disease in sow herds, leading to aborted fetuses, piglet mortality and sow mortality.

The other challenge these viruses have presented is the difficulty in eliminating them from sow farms. The “traditional” 210- to 240-day closures designed to eliminate PRRSv from a breed-to-wean farm have not been as successful, forcing many producers to make a decision on whether to keep a herd closed longer in hopes of eliminating the virus or to reload the farm and restart the elimination procedures over again in an effort to not miss production targets.

Research on these viruses and how they are transmitted within a herd has shown that these newer strains are shed for a longer period and are shed in higher amounts from infected animals. There also is speculation that new viruses are able to change more quickly within a population. All of these factors have worked to decrease the success of PRRSv elimination in breed-to-wean herds.

The effects of an increasingly pathogenic virus also can be seen in growing pigs. PRRSv 1-7-4 and 1-3-4 infection in growing pigs continues to be severe, causing greater mortality with higher culling rates and increased treatment costs compared to PRRSv strains observed in the past.

Similar to the observations in sow farms regarding the timing of disease, the effects of PRRSv infection seem to extend to longer periods compared to past PRRSv strains. Nursery and finishing sites that are continuous flow struggle tremendously to eliminate the virus and should consider all-in/all-out or, at the very least, site depopulation to eliminate virus from these populations of growing pigs.


The cornerstone of preventing new virus introduction still relies on biosecurity, biosecurity, biosecurity.

Even though newer strains of PRRSv act increasingly pathogenic, sound biosecurity practices — including clean/ dirty lines for site entry, controlled supply entry, organized (clean to dirty) personal movement, dedicated trailers, mortality composting, etc. — help limit virus spread from farm to farm.

Air filtration of breed-to-wean farms continues to be successful. Filtration hasn’t been 100% effective in all cases, but when looking at dense areas where sow herds were breaking multiple times each year, the reduction in the outbreak rate has been extraordinary. Updated technologies, including positive-pressure filtration systems and air conditioning, which reduces the amount of air that needs to come into the barn, continue to move the bar on what can be expected for preventing virus introduction into these farms.

A PRRSv vaccine remains an important tool available to producers for virus control. Recent additions of modified live PRRS vaccines on the market give swine producers further options for vaccines.

In many commercial sow herds, especially those in more densely populated swine areas, a modified live vaccine is used to help maintain immunity at least with the goal of lessening the impact a new virus introduction will have on the herd. In many of these cases, the herds and replacement gilts are vaccinated multiple times each year to maintain immunity.

In growing pigs, millions of pigs continue to be vaccinated for PRRSv (either prior to weaning or at some point while in the nursery). PRRSv vaccines continue to show the ability to reduce lung lesions for pigs that become infected with a non-vaccine strain of the virus. In addition, groups that are vaccinated and exposed to a field virus consistently show closeouts that have less mortality and a lower cull rate compared to nonvaccinated groups that become infected with field strains.

As an industry, we’ll start to see the benefits of new diagnostic technologies, including whole-genome sequencing, which will provide more insight than ever before regarding PRRS circulation and change within a population. Take, for example, herds that are unsuccessful at eliminating a resident PRRSv strain from their herd. Whole-genome sequencing will help determine if that virus continues to be the resident strain or if a completely new virus strain has been introduced into the herd.

It goes without saying that it has been and will continue to be an interesting time for all swine producers. The industry is already starting to make market pigs for June 2020. It’s paramount to keep PRRSv out of the herd. Those producers who are able to limit new virus entry will have a greater opportunity to keep reducing pig mortality and culls, leading to increased profitability.

PRRSv “season” will be here soon, so it’s important to emphasize that the biosecurity practices producers have used for years for PRRSv and other pathogens still apply.

Reprinted with permission of Feedstuffs.

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