How to manage herd closure for PRRS elimination

Herd closures to eliminate porcine reproductive and respiratory syndrome (PRRS) are on the increase due in part to the virulent variant identified as PRRS 1-4-4 L1C.

“PRRS 1-4-4 L1C has hit people hard,” reported Paul Yeske, DVM, Swine Vet Center in St. Peter, Minnesota. “The elimination process for this variant is what we’ve done for all PRRS viruses, and the program has been very successful at getting the herd to make PRRS-negative pigs.”

Yeske offered suggestions for a successful herd closure to eliminate PRRS from a farm.

Prepare for herd closure

The first step is increasing gilt inventory to cover the full closure time, which typically runs 210 to 240 days, according to Yeske.

“If there’s an on-site gilt developer where the farm is getting the gilts as Isoweans, they already have 6 months of gilts and only need to increase capacity for a couple months,” he said. If the farm has no on-site gilt development, they must either find another site to hold these animals or be able to fill the space available and live with the current inventory.

Just prior to closure, Yeske recommended implementing a feedback program that’s given to all sows and gilts to provide scour control for 6 to 8 months of the closure. “A lesson learned from PED (porcine epidemic diarrhea) was that we can help ourselves on scour control by doing a whole-herd feedback at the beginning of a herd closure,” he said.

Closure begins

Herd closure begins when sows are exposed with serum collected from the farm site. This occurs after the sow herd has recovered from the initial break and are eating and feeling good again. Some farms even wait until all replacements are on site.

He suggested following up 3 weeks later with a statistical sampling around the site to confirm the herd is positive. Make sure to obtain tests from all barns to ensure all animals are positive going forward.

“The injections start the clock ticking for 240 days and maybe longer, depending on how testing goes,” Yeske said. “Essentially, we wait for time to allow immunity to develop and shedding from sows to decrease.

“The theory is the virus will shed for a period of time, and the immune system will clear the virus from the sows,” he explained. “Since there are no animals in the herd that can be infected, theoretically the virus should die out on the farm, allowing for negative replacements to enter and not become infected.”

Throughout the herd closure, Yeske said the farm should focus on cleaning and disinfecting rooms, hallways, loadouts and any place weaned pigs move. Also, movement between litters should be minimized, and staff should be diligent about changing boots and coveralls when going back to handling young pigs. They should always work from youngest to oldest pigs, and change and clean up before going back to younger pigs.

Testing regimens

After 10 to 12 weeks of closure, collecting and testing piglet processing fluids begins, which will indicate the level of viremia in piglets. “Are we still positive or are we going negative?” he said. “We watch the Ct (cycle threshold) values and hope to see them go up. A lower number means more virus in the sample.”

Yeske recommended using processing fluids because samples are relatively easy to obtain, and it is less expensive than other testing methods. Plus, it essentially tests all piglets in a pooled sample, he added. Most farms pool a week’s worth of samples to reduce cost, yet still monitor to see if the herd is progressing.

When processing fluids start testing PRRS-negative, then piglets should be tested at weaning to see if they have remained negative through lactation. At this point, processing-fluid samples should be tested by room or day to help isolate the positive locations.

“Before weaning, most do blood testing, but you can use family oral fluids,” Yeske said. “With family oral fluids, hang the rope so the sow can chew on it first, and the piglets will chew on it too. Some litters respond better to family oral fluids than others, which is why most will use blood samples.

“The other option is to blood test the poorest-quality pigs, 30 to 60 a week or month, to establish if pigs are negative at weaning,” he added.

When to open herd

Depending on the farm, some use 60 days of negative tests at weaning, and others use 90 days of negative tests before ending the closure, according to Yeske.

“What we’ve seen is 210 days is the sweet spot for herd closures,” he said. “We tried 180 days and didn’t have good success. If you use 210 days, you have higher confidence that the herd is ready to take PRRS-negative gilts.

“And if you don’t get the piglets testing negative at 210 days, then we just wait. That’s when some people go to 240 days or longer. Remember, time is your friend in elimination programs versus ending the closure too soon.”

Closure ends

Once the closure is finished, the final step is repopulating. If a genetic supplier for a farm with an on-site gilt developer can provide a staged population, Yeske recommended refilling the gilt developer that way.

If only weaned pigs are available from the supplier to repopulate the herd, the farm will need a clean place to raise clean animals. “That’s a potential limitation, and you must think about that going into an elimination,” he said.

“Overall, the process of PRRS elimination is relatively inexpensive. And it’s been able to push the field virus out of herds,” Yeske added. “Some farms in pig-dense areas will maintain a vaccination status. They will be negative to the field virus but have a PRRS vaccine to have some herd immunity in case of a new virus exposure.”



Weaned-pig market heats up after PRRS 1-4-4 outbreaks

A strong weaned-pig market this summer indicates the magnitude of the porcine reproductive and respiratory syndrome (PRRS) 1-4-4 variant outbreak in the US pork industry.

“There’s been enough PRRS breaks and death loss that people have to buy weaned pigs to fill their barns and contract obligations,” reported Ryan Strobel, DVM, Swine Vet Center. “When we see weaned pigs still being sold in the middle of the summer for $45 to $50, it shows there’s demand and people are having health problems with their flows.”

When disease affects markets

On rare occasions, disease outbreaks become severe enough to move hog markets. For example, the porcine epidemic diarrhea (PED) outbreak in 2014 and porcine circovirus in the mid-2000s both impacted hog numbers enough to change markets, Strobel said.

Will the PRRS variant impact US markets this fall and winter? While he stressed he isn’t a market analyst, Strobel said the PRRS variant’s impact on hog farms in May and June led him to believe markets in December and January could be abnormal.

“Given the amount of spikes and outbreaks we had, PRRS 1-4-4 could be a market mover,” he said. “It will be interesting to see what the numbers come in at this winter with higher demand than normal.”

Weaned-pig buying advice

The hot weaned-pig market means it can be challenging to find and buy healthy pigs.

“Make sure you do due diligence when purchasing weaned pigs,” he explained. “There are a lot of mistakes made when buying open-market pigs.”

Strobel suggested producers learn as much detail as possible about the health of the weaned pigs before buying. Be sure to ask questions about the major diseases like PRRS, PED and Mycoplasma and follow-up on other diseases like Escherichia coli and Streptococcus suis. He also recommended asking for references from other growers or the owners of previous groups of pigs.

“The PRRS 1-4-4 impact has also left more open contract-grower barns, especially compared to last year when there were no barns available,” he added.

Lessening the impact

With the current market climate, Strobel believes this is a good time to consider hedging for risk protection. “Despite what the numbers say or how optimistic we are, it’s good to manage risk,” he said. “Protecting a certain portion of your production is always a good idea.”

He also thinks this is a good time to reevaluate vaccine programs, especially with all the health challenges facing pigs. “More people are relooking at vaccination programs, whether going to a full dose or readjusting how they give vaccines or the timing,” he said.

“What we did a year ago is obviously different from what we are doing today,” Strobel added. “It’s crazy to think a year ago you could buy a weaned pig for free or $5, and now they are $50.”

Nasty PRRS variant continues to spread undeterred by summer’s heat

The virulent porcine reproductive and respiratory syndrome (PRRS) variant identified as PRRS 1-4-4 continues its destructive march through hog farms, even in the heat of summer.

The PRRS variant first struck herds in Minnesota and northern Iowa this past winter, and while producers and veterinarians hoped it would calm down in warm weather, latest data suggests things aren’t so simple.

“Even when it was 99°, we were getting calls about PRRS breaks,” reported Laura Bruner, DVM, with Swine Vet Center in St. Peter, Minnesota.

“It’s unprecedented; it’s unusual,” she continued. “This virus is walking past normal biosecurity practices such as on-farm biosecurity, trucking biosecurity, air filtration and feed mitigation.”

Survey shows variant’s hot spread

Alarmed by the continued PRRS 1-4-4 outbreaks, Bruner surveyed her peers of 15 veterinarians in the US to understand the variant’s reach. She was shocked by the results.

“In just over a month during the warm time of the year, we had 107,000 sows break with PRRS 1-4-4, and I believe that is an underestimation,” Bruner said.

“When you talk to practitioners about it, they have farms breaking with the variant that have never broke with PRRS before, and for some farms it’s been decades or never.

“Also interesting is how many nursery breaks there are,” she continued. “I can count on both hands in my career how many lateral field infections have happened in the nursery. It has caused more mortality and makes these nursery pigs quite a bit sicker than what we have seen other viruses do in the past.”

Another unusual detail of these outbreaks is the consistency of the PRRS 1-4-4 variant.

“Historically, if you have a sow-farm break, you call another veterinarian and compare sequences,” Bruner explained. “Rarely do they match. But with this one, it’s frequently over 99% to 100% a match. I had one farm in southern Minnesota that was a 100% match to a PRRS virus in northern Minnesota.”

Time to collaborate

Armed with her PRRS 1-4-4 survey results, Bruner sought help from Cesar Corzo, DVM, at the University of Minnesota. Corzo works with the Morrison Swine Health Monitoring Project, which monitors the incidence of swine disease such as PRRS. He set up a meeting at World Pork Expo (WPX) with other veterinarians and swine disease researchers to discuss the PRRS variant.

“My purpose of getting that meeting together was to collaborate and learn from each other,” Bruner said.

“We’ve learned we don’t know everything about PRRS, and specifically this virus because it does seem to be different. It is a game changer, just like PED (porcine epidemic diarrhea) when it arrived.”

Bruner hopes new research discussed during the WPX meeting will shed light on the variant’s unusual virulence. But for now, collaboration among practitioners will help fill in answers.

“We need to learn from who breaks with 1-4-4 and who doesn’t,” she said. “And we need to learn the successes and failures of their investigations.

“We need to go all the way back to the beginning and ask: Do our normal biosecurity practices work? Does our normal disinfection work? Do the filters we use today work? What’s different?”

Tighten biosecurity

With the variant’s threat to hog farms, Bruner recommends producers use this as an opportunity to improve biosecurity on the farm.

“Take a hard look at your biosecurity for any weaknesses and get them corrected,” she said. “We need to be looking at all the major inputs into the farm like people, feed, water and air as a source of infection.

“We are unsure of feed as a route of entry and haven’t done research on PRRS specifically in feed. I think it is worth considering a feed mitigant for sow farms and gilt-development units. We know that there are ingredients that provide a better environment for virus survivability than others and those need to be investigated.”

For farms that broke with PRRS 1-4-4 last winter, Bruner said it is still too early to know if the virus leaves the farm or if it will be difficult to eradicate.

For more information about PRRS 1-4-4, visit:

Highly infectious PRRS variant causes high mortalities on sow farms

New PRRS 1-4-4 L1C variant presents dramatic symptoms, quick spread

Virulent PRRS outbreaks in grow-finish require fast action to cut losses





Highly infectious PRRS variant causes high mortalities on sow farms

A variant of the porcine reproductive and respiratory syndrome (PRRS) virus is taking a heavy toll on hog farms in southern Minnesota and northern Iowa. The variant, identified as PRRS 1-4-4, hits sow farms especially hard, causing 10% to 20% sow mortality and high mortalities in the nursery of 50% and even as high as 80%. In grow-finish units, mortalities are less but still can be significant, and growth rates drop dramatically.

“This PRRS virus hasn’t done anything we haven’t seen with PRRS; it’s just way more dramatic,” reported Paul Yeske, DVM, Swine Vet Center, St. Peter, Minnesota. Yeske talked about PRRS 1-4-4 as part of a webinar presented by the Swine Health Information Center and American Association of Swine Veterinarians.

Clinical signs

“From what we’ve seen on sow farms, this virus has a pretty distinct footprint,” Yeske explained. “You almost don’t have to wait for sequencing because you know what it looks like from the clinical signs.”

Symptoms include sows going off feed, abortions, increased sow mortality, increased piglet mortality, increased mummies and high post-weaning mortality.

“One thing that’s unique to this virus is it tends to move quickly through the herds once you see clinical signs,” he added. “You’ll start with four to five animals off feed and then 200 the next day and 300 the next. It marches through the herd quickly.

“The abortions start about the same time the animals go off feed. We’ve seen upwards of 3 to 5 weeks of production aborted and 10% to 20% of the sows dying in 2 to 3 weeks.

“Also, there’s high piglet mortality in the farrowing house…50% up to 80%, which I didn’t think was possible.”

In addition, neither vaccination nor prior exposure to the virus appears to reduce the outbreaks, he added, but it’s difficult to tell with the limited number of herds experiencing an outbreak.

High viremia

The PRRS 1-4-4 variant produces high levels of viremia, allowing it to spread easily in an area, Yeske explained. In addition, a milder winter with overcast, warm weather has helped the virus move around.

An increased number of diagnoses started in October 2020 in the two-state area, beginning with outbreaks in grow-finish sites and moving into sow farms.

“Certainly, the worst breaks have been, like we always see with PRRS, when you have viremic pigs leaving the sow farms,” he added. “But with this virus, we have lateral outbreaks even at the end of nursery with significant mortality.”

Yeske indicated some of the farms that broke were filtered, while others stayed negative even when located next to positive finishing sites and lots of positive pigs.

“Filters continue to show us they help but are not perfect,” he added. “The PRRS viral load is very high. There are lots of opportunities for this virus to get in, and if there’s a weakness, it’s likely going to find it.”

Stabilizing herds

After a 2- to 4-week period where herds experience the devastating losses, farms start to stabilize.

“We see sows start to return to normal,” Yeske said. “We see normal pigs born again but with very low, live born due to mummies, even though total born are still in the 16 to 17 pigs range. There are a lot of mummies on these farms but not necessarily all farms.”

As the herds continue to stabilize, Yeske said they will track them on the PRRS timeline to see if it runs similar to other strains they have dealt with in the past.

Review biosecurity

The big lesson Yeske hopes producers will learn from these outbreaks is the importance of a biosecurity plan that is strictly followed. He urges everyone to review their biosecurity.

“Identify the greatest area of risk in your herd,” he explained. “Risk is how likely something is to come into the herd and then how many times a week do you do that activity. Multiply those two to give you the risk.

“Then improve any weakness in your biosecurity system, and do it sooner rather than later,” he added. “Don’t wait to identify it in your outbreak investigation.”



Virulent PRRS outbreaks in grow-finish require fast action to cut losses

A particularly difficult variant of the porcine reproductive and respiratory syndrome (PRRS) virus recently hit hog farms in south-central Minnesota. Henry Johnson, DVM, with Swine Vet Center in St. Peter, Minnesota, was called to diagnose and treat the PRRS outbreaks on client farms.

The virus has been identified as PRRS 1-4-4 and, to date, is the most virulent PRRS variant to infect hogs in the US.

“More herds have gotten infected, and this PRRS strain seems to be extremely pathogenic and more prone to airborne transmission,” Johnson said.

When it affects grow-finish units, he recommends immediate and aggressive treatment to reduce mortalities.

First symptoms

“When you walk into a PRRS 1-4-4 outbreak, you see a lot of pigs with varying degrees of respiratory challenge,” Johnson explained. Often, he sees pigs “thumping,” where the animals labor to breathe through airways blocked by bacterial and viral pneumonias.

“Other times, pigs are very, very lethargic because PRRS attacks and disables the whole immune system in pigs,” he said.

An outbreak can be identified early if grow-finish units are tracking water consumption. Pigs will quit drinking first, causing a dramatic drop-off in water usage. This should signal the need to start intensive pig care immediately, Johnson noted.

These symptoms may affect 5% to 25% of the pigs, depending on where they are in the disease challenge.

Diagnose, separate sick pigs

Johnson’s first action is to gather samples and send them to a diagnostic lab. The PRRS virus strain needs to be verified, and secondary bacterial infections identified.

“Get good bacteriology and susceptibility information from the lab, so you can make better microbial decisions and have confidence that you are putting the right medication for the right bug and utilize it appropriately,” he said. “It’s also good, judicious antibiotic use.”

At the same time, he wants to be aggressive and get help started for ailing pigs. He recommends moving critically ill pigs to sick pens for individual care.

“The best thing to do is provide a warm, dry, comfortable area with less pressure and competition for feed, water and space,” Johnson said. “Pigs can recover and subsequently move back to the general population where they are mixed in with other pigs. Then you can cycle other pigs through that sick pen.”

Another immediate action should be to increase barn temperatures, especially for young pigs. Pigs rarely die from being too warm in the winter during the nursery phase but can die of complications from being too cold.

Suppress secondary bugs

“A lot of times with these nasty PRRS [outbreaks], you are already behind the eight ball when you start,” he said. “You will never cure viral disease with an antibiotic. You are just trying to suppress secondary bacterial infections and control them when the immune system is devastated and rebooting after going through the PRRS infection.”

Depending on the herd and challenge, Johnson said they will use different antibiotics and delivery methods. He recommends starting water medication right away to address common secondary bugs like Streptococcus Suis, Glasser’s disease, Mycoplasma hyopneumoniae and Pasteurella.

When pigs are unable to get up to drink, Johnson recommends a mass injection followed by oral antibiotics or water medications.

“A lot of focus for me is to make sure we use the right antibiotics and follow up with caregivers to make sure the pigs that need help are moved and getting the necessary care,” he said.

Even with these care regimens, mortalities can still be high. He estimates as much as 15% mortality can occur.

Biosecurity alert

“When you get a virus that is really severe like this and spreads quickly across multiple production systems and geographies, it is a wake-up call to biosecurity practices in grow-finish,” Johnson said.

If any labor or equipment is shared, make sure all parties involved know what is going on. It’s also good to keep the feed mill in the loop as well.

“It’s a hard culture to establish, but if you are able to reduce a break like this, it demonstrates the importance of keeping our barns clean,” he said.