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.

 

 

 

 

 

 

Antibiotics properly timed during PRRS virus outbreak reduce reproductive failure

An outbreak of porcine reproductive and respiratory syndrome (PRRS) on a sow farm will trigger reproductive failure in gestating sows. While PRRS is a viral disease, it causes endometrial inflammation leading to abortions, stillborns and mummified fetuses.

Ross Kiehne, DVM, with Swine Vet Center, conducted a study to evaluate the use of the injectable antimicrobial Draxxin® (tulathromycin) administered to gestating sows during a PRRS virus outbreak. Specifically, he wanted to see how administering the antibiotic at different stages of gestation affected the rate of reproductive failure.

On-farm investigation

The investigation was conducted on a 2,500-sow farm in northeast Iowa that broke with PRRS virus in mid-2019. The first 5-mL dose of Draxxin was administered to gestating sows 5 days after the outbreak was detected. A live viral inoculation (LVI) was performed 2 days later. A second round of the antibiotic was administered 13 days after LVI. About 20% of the sows were not treated, and these animals served as a control.

Data collected for the study was based on the pregnancy stage when the first antibiotic treatment was administered. The gestation stages were day 0-18, day 19-29, day 30-49, day 50-69, day 70-90 and day 91-105.

Kiehne used four reproductive outcomes for analysis: 1) abortions, culls and death; 2) farrowed and found open; 3) preg-check negative; or 4) repeat mating. The number of pigs weaned per sow was also determined for each animal enrolled in the study.

Positive outcomes in later gestation

The study verified Kiehne’s hypothesis that while administering Draxxin during early gestation is detrimental, it is beneficial during later gestation.

“Administering this antibiotic during early pregnancy appears to increase negative outcome events such as found open, preg-check negative and repeat mating,” Kiehne said.

“However, there appears to be an advantage to administering it in a PRRS virus situation after 50 days of gestation,” he continued. “This advantage is apparent in a reduction in abortions, stillborns and mummified fetuses and increase in total pigs weaned.”

Overall, the study found the percentage of sows that farrowed was higher for those given the Draxxin treatment at 68.5% versus 64.1% for the control sows with no antibiotic. Sows with abortions was lower for those receiving the Draxxin treatment at 17.4% versus 22.9% for the control group. Sows not pregnant was 6.9% for those given the Draxxin treatment and 6.7% for the control group. The deads and culls category was 7.2% for sows receiving the Draxxin treatment and 6.3% for the control group.

Weaned pigs per enrolled sow was calculated in each pregnancy group. In the early pregnancy stages, weaned pig averages were lower for sows receiving the Draxxin treatment compared to controls. After day 50 of gestation, the number of weaned pigs increased for sows receiving the Draxxin treatment compared to the control group.

In conclusion, Kiehne recommends administering the injectable antimicrobial Draxxin to sows after day 50 of gestation during a PRRS virus outbreak. However, administering it any earlier would be detrimental.

 

 

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

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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.”

 

 

Is reducing inflammation key to improving PRRS control?

By JoAnn Alumbaugh
Farm Journal’s Pork

Porcine reproductive and respiratory syndrome (PRRS) continues to be a critical concern to the U.S. pork industry. The combined production losses associated with PRRS in breeding and growing-pig herds are estimated at more than $663 million, and that doesn’t include secondary infections.

There is usually a high degree of interaction between pathogens, and it has been shown in previous studies that a reduction in PRRS also causes a reduction in the impact of co-infections like Streptococcus suis, Haemophilus parasuis, Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae and Salmonella spp.

PRRS is a viral disease, yet it is known to cause considerable inflammation in the respiratory system. In PRRS-infected gilts, endometrial inflammation and vasculitis increased progressively from 2 to 14 days post-inoculation.

Inflammation may be one of the factors associated with abortions in the presence of PRRS as well. Inflammation at the point of attachment of the uterus with the placenta may disrupt the fetus, resulting in loss of the fetus or the formation of the mummy, says Paul Yeske, DVM, with the Swine Vet Center in St. Peter, MN.

“There are certainly some things we don’t understand, and we have changed our thought processes on how we can manage these things,” Yeske says, adding that PRRS-infected pigs are more vulnerable to secondary bacterial infections requiring an antibiotic therapy, so having an antibiotic and an anti-inflammatory can be a good combination.

“The inflammatory response is a call to action of the whole pig,” says John Deen, DVM, PhD, professor at the University of Minnesota. “It affects behavior, reproduction, metabolism and even the pig’s ability to survive. It has to be taken seriously, especially in the face of a disease like PRRS. We need to provide extra care for animals to recognize when they cannot cope with the insults they have in front of them.”

Inflammation is usually associated with bacterial infections; in which case an antibiotic would be used to help reduce the inflammation that accompanies an infection. Now, researchers are learning more about the role of inflammation in viral infections like PRRS.

Research findings

Andre Buret, PhD, a professor in the department of biological sciences at the University of Calgary, Canada, has done extensive research on the immunomodulation properties of an injectable antibiotic on pigs infected with PRRS. Immunomodulation refers to a change in the body’s immune system, caused by agents that activate or suppress its function.

While no vaccine against PRRS provides 100% protection, some injectable antibiotics have been shown to exhibit potent immune-modulating effects — that is, they activate, boost or restore normal immune function once it’s damaged. That in turn can help better withstand the inflammatory responses associated with PRRS.

“Treatment options to control PRRS outbreaks are limited, and the efficacy of vaccines is thwarted by the antigenic variability of PRRSV,” Buret says.

He explains that PRRS can create immune dysregulation — a breakdown of the immune system, in other words — that makes the host more susceptible to opportunistic pathogens. Disease severity is closely related to the ability of the virus to disrupt the functions of the macrophage — a large white blood cell that is an important part of the immune system — and induce inflammation, he adds. For those reasons, he theorizes that targeting inflammation with an antibiotic used for bacterial co-infections might be a critical element in managing the costly PRRS virus.

In laboratory experiments conducted by Buret and his team, using an injectable macrolide antibiotic did not change intracellular or extracellular viral titers, nor did it alter expression of the viral receptors (CD163 and CD169) on porcine macrophages. It did yield other benefits, however.

“In contrast, [the antibiotic] exhibited potent immunomodulating properties, which therefore occurred in the absence of any direct antiviral effects against PRRSV,” Buret says. “These data demonstrate that [the injectable antibiotic used in the study] inhibits PRRSV-induced inflammatory responses in porcine macrophages and protects against the phagocytic impairment caused by the virus.”

The antibiotic was also shown to inhibit the production of pro-inflammatory mediators (CXCL-8, LTB4) and promote the production of pro-resolving mediators (LXA4), Buret explains.

Research evolution

Buret’s work with pigs and PRRS marked an evolution in the battle against the PRRS virus.

“We spent two and a half years of research…and we were able to demonstrate [the antibiotic] may very well have benefits in the context of PRRS viral infections based on what we discovered,” he says. “It seems to disarm the ability of the virus to prevent host immunity to clean up bacteria in the lungs.”

If a producer has the background of a viral infection like PRRS on the farm, the engulfment of foreign particles by the macrophages is compromised. As a result, the lung cannot clean itself anymore and the pigs are more prone to secondary infections, Buret says.

“The virus alone triggers an inflammatory response and impairs phagocytic clearance by macrophages. We observed that this type of antibiotic protects against both effects. It’s really one discovery leading to the next,” he adds.

“As it turns out, our discoveries have established for the first time that controlling inflammation at the same time as you control the microbe is the best way to deal with these diseases clinically,” Buret says.

Anecdotal evidence

Swine Vet Center’s Yeske recalls working with a client who had a PRRS break in a herd that was being treated with an antibiotic as part of a Mycoplasma hyopneumoniae (M. hyo) elimination program.

“We were treating the herd with an antibiotic [for M. hyo] and [it] broke with PRRS in the middle of the M. hyo elimination,” Yeske says. “You never know if an outbreak is going to be as severe from herd to herd as other similar outbreaks, even if the virus is similar, but we saw much less of an impact in this particular case as we went through and treated the animals for the M. hyo elimination. We had fewer clinical signs than we would have expected to see, based on other very similar farms that had essentially the same virus. It does make us think about some of the mechanisms that may be going on [associated with inflammation].”

Because PRRS is often a co-infection with bacterial infections that also cause inflammation, antibiotic treatments for M. hyo might yield secondary benefits that make the effects of PRRS less severe.

This is a new approach for veterinarians to consider when PRRS is present in herds infected with swine respiratory disease, Buret says. The antibiotic controlled the bacterial infection, which in turn helped to not only reduce inflammation but also the host’s response to it — a process that, if left unchecked, ultimately causes pulmonary failure and death.

“Research in live pigs is warranted to assess the potential clinical benefits of this antibiotic in the context of virally induced inflammation and tissue injury,” Buret says.

(Read the article at Farm Journal’s PORK.)