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Filters Are First Line Of Defense Against PRRS

Carthage Veterinary Service Ltd. of Carthage, IL, believes adding HEPA air filters to boar studs screens out the virus that causes porcine reproductive and respiratory syndrome (PRRS), providing an extra margin of security against contamination of sow farms. Carthage Veterinary Service Ltd. (CVS) coordinates shipments of semen from two producer-owned boar studs to 110,000 sows across Illinois, Iowa

Carthage Veterinary Service Ltd. of Carthage, IL, believes adding HEPA air filters to boar studs screens out the virus that causes porcine reproductive and respiratory syndrome (PRRS), providing an extra margin of security against contamination of sow farms.

Carthage Veterinary Service Ltd. (CVS) coordinates shipments of semen from two producer-owned boar studs to 110,000 sows across Illinois, Iowa and Missouri.

Many of the pigs produced by this semen are shipped as weaners to Iowa and Minnesota for finishing.

To provide the highest level of biosecurity for their clients, CVS has instituted a very detailed set of guidelines and rules for the boar studs (see sidebar on page 11).

In the past year, CVS went the extra mile, installing a HEPA filtration system in the second boar stud, with plans to install a similar system in a third, 400-head boar stud planned for construction later this summer.

HEPA stands for High Efficiency Particulate Arrestance, and refers to technology developed during World War II to remove radioactive particles from the air that could be dangerous to researchers.

Joe Connor, DVM, and co-owner of CVS, says HEPA air filtration systems have proven to be the most effective means of keeping out the PRRS virus. “As far as we know, there has never been a boar stud in the world that has broken with PRRS virus that has had (HEPA-) filtered air,” he reports.

In a number of boar studs in Europe, HEPA air filtration technology has been used successfully for many years to address hog density issues and PRRS infection re-breaks, he says.

Numerous boar studs in the United States have broken with PRRS over the years, including a spate of breaks this past winter. None of those studs, including a break in a Minnesota boar stud this summer, used air filtration systems, Connor adds.

Bear Creek Genetics, LLC

In 1998, about 24 tri-state area producers set up a limited liability company as a user group to build boar studs under the name Bear Creek Genetics, LLC. The first stud of 270 boars was built near Quincy, IL, that same year. It broke with PRRS over the Christmas holidays in 2000-2001, recalls Doug Groth, veterinarian in charge of boar studs and biosecurity for the Carthage veterinary/management group.

Soon after that the stud was emptied and repopulated. It has not re-broken with PRRS in the intervening years, despite being situated in a hog-dense area near a four-lane highway that was completed after the stud was built, Groth explains.

To provide more health assurances for producer-owners, it was decided that the second boar stud should be filtered. Located near Bowen, IL, it is an H-shaped facility that was built in two phases, with 200 boars housed on each side of a center office area. The first leg of the stud of 200 boars was completed in 2002. When the second wing of 200 boars was built a year ago, HEPA filtration technology became available and was installed to help protect the stud from PRRS, particularly because it produces a maternal line of boars, says Groth.

Shortly thereafter, the original phase of the second stud was retrofitted with HEPA filters to provide positive-pressure ventilation throughout the whole boar stud.

“With HEPA filters, we set them up as positive-pressure, tunnel-ventilated systems so we force outside air in through the HEPA filter that is higher pressure than anything on the outside of the building,” he says. “If there is a 30-mph wind outside, I don't want it blowing back in my exhaust outlets, so I have to maintain a positive pressure compared to the outside.”

The studs also feature cool cells on the end of the buildings, plus misters and stir fans to keep boars relatively cool on the hottest days in summer.

The ‘HEPA Room’

Groth says to convert a standard, negative-pressure ventilation system to a positive-pressure system for HEPA filtration in the older section of the second boar stud actually required that a separate “HEPA room” be built.

First is a panel of cool cells on the outside wall of the 15-ft-addition. Inside is a bank of four, 6-sq.-ft. metal air plenum chambers that house the electric fans that pressurize the air so it can be forced through the large HEPA filters into the main room of the boar stud. A series of 2-in.-thick pre-filters capture large particles such as dust and bugs, before air reaches the HEPA filters. There are nine HEPA filters in each air plenum.

HEPA filters are about 2 ft. sq. and a foot thick and consist of a “metal frame with a lot of pleats,” explains Groth. “They are 99.9% efficient in capturing most dust and virus particles down to 0.3 microns. The air coming through is as clean as you see in hospital rooms.”

HEPA filters and the prefilters can both be purchased from a number of commercial ventilation companies.

Each air plenum chamber operates independently, says Groth, so if routine maintenance needs to be performed, or a motor freezes up in one of the plenums, that chamber can easily be shut down at the computer-operated control pad.

Meanwhile, the other chambers continue to function normally, keeping air flowing and filtering systems working. The heating system is also engineered to run through the HEPA filter system.

A standby generator can be activated in the case of a power outage.

Energy, Filter Costs

In comparing energy use in the first, non-filtered boar stud vs. the second, filtered stud, there is surprisingly little difference in cost.

Boar studs cost about $3,000/boar to build. It cost around $600/boar to install the HEPA air filter system in the second boar stud.

Each HEPA filter costs from $200 to $400 and prefilters run $8/each. Prefilters need to be checked and changed about every quarter, while the HEPA filters are still functioning properly and have yet to be changed after one year of operation, remarks Groth.

He says some adjustments will be made to reduce the cost of installing the filter system to around $400/boar for the third boar stud. Key will be using one set of controls instead of two, because the third stud will only have six air plenums, compared to seven at the second boar stud.

“When we put in four air plenums in the original construction of the second half of the second boar stud, we never got above 60% capacity on each of the air plenum units,” says Groth. “We found out it wasn't necessary to have that fourth plenum and the 30% or so extra capacity.”

Testing Results Positive So Far

Veterinarians Groth and Connor caution it's only been a year since the HEPA filters were installed at the second stud, and there is no real way to know their true impact. But they believe that the filters have at least contributed to keeping out PRRS virus so far.

Semen collection is done at night when boars can stay cooler, especially beneficial in summer. Semen is collected four nights a week.

To test for PRRS, every third boar collected is serum-tested during semen collection using the ear prick method developed by Darwin Reicks, DVM, Swine Vet Center, St. Peter, MN.

But instead of using the ear swab to collect serum, Groth has switched to a plastic tube that uses capillary action to suck blood from the ear vein. It improves the quality of blood samples, reduces contamination and ensures adequate quantity, he says. Blood samples go out fresh early the next morning to the University of Illinois diagnostic lab at Champaign-Urbana. Results are e-mailed to the clinic by 5-6 p.m.

As assurances grow, testing will be reduced, which will in turn reduce the added cost/dose of semen to customers, says Groth. Testing by polymerase chain reaction (PCR) costs $22-25/sample.

Maternal and terminal boar semen are serum-tested for PRRS, both pooled in groups of five boars. For a “suspect” serum sample, each of those five boars would be tested individually.

Groth emphasizes that all five boars would be immediately sent to market if a pooled sample initially tested PRRS positive. “I don't care about five boars compared to 400 boars on one site,” he notes. “Suspects” sometimes occur in PRRS testing, and could point to a low-level infection, but more likely mean something didn't turn out right with the testing procedure.

“There is a standing order at the stud that when staff get an e-mail notifying of a test result pending or a suspect sample, employees are to automatically repeat the sampling procedures and send them off so they arrive at the diagnostic lab by noon the next day,” says Groth. Stud staff are trained to bleed boars from the jugular vein for followup PRRS tests.

Boar Stud Biosecurity Measures

Doug Groth, DVM, Carthage Veterinary Service, Ltd., says HEPA air filtration is really only a part of the biosecurity equation at the Bear Creek boar studs, in west central Illinois.

“We said we were going to do everything we can to protect the boar stud because of the large number of sows that we are servicing, and that is what we are doing,” he asserts.

Starts with the Boars

Biosecurity is for boars, too. PIC boars are introduced to the studs 5-6 times/year at 6-7 months of age from PIC trailers that have been through a cleaning and baking procedure.

Each stud has a separate 40-head (first stud) and 48-head (second stud) isolation building where boars spend their first 45 days becoming acclimated and trained for collection.

They are vaccinated for parvovirus, leptovirus and erysipelas and swine influenza virus. Boars are bled twice upon entry, and when they leave isolation, for porcine reproductive and respiratory syndrome, pseudorabies and brucellosis.

Boars are transported by designated trailer from an on-site equipment barn a few hundred feet to the main boar stud, after isolation/acclimation are completed, explains Groth.

When boars are culled, each stud has its own designated clean hog cart or trailer to load up and haul culls off-site. They are loaded onto a different clean trailer a mile or more away to ship to market.

Cull boars are shipped about once a week. Cull trailers are never allowed on the boar stud site, stresses Groth. And cull boars are always removed at the end of the day so employees working with them can go home for the day to create downtime.

Limiting Traffic

Visitors are strongly restricted from contact with boars in the stud. Groth jokes the visitor's log simply reflects his many visits to the stud.

But actually, biosecurity restrictions are serious business — Groth and others must strictly follow a 48-hour downtime between visits to the studs. That means he may in fact only get to visit each stud once a week or less.

Employees can travel between the first and second boar studs, provided there is 24-hour downtime.

All people traffic must shower in and out of the stud. If anyone steps outside the stud for any reason, they must shower back in. One employee was fired for not doing so.

“We are serious about biosecurity, because if something contaminates the stud and we can't sell semen, there is no cash flow,” says Groth.

All exterior doors are clearly marked “do not enter” and kept locked.

Stud labs for semen analysis are operated as separate shower-in, shower-out facilities. The second stud uses an underground pneumatic tube to transport semen shipments from the collection area to the lab.

Other Measures

  • Perimeter fencing and charged, high-tensile wire fencing surround the first and second boar studs, respectively.

  • All supplies entering the stud are fogged and disinfected prior to use.

  • Feed is delivered first thing Monday morning to a bulk bin about 150 ft. away from any stud buildings, and flows through feed lines into the feeders.

  • Building perimeters are kept well-landscaped and rocked. Bait stations are positioned at least every 50 ft. for rodent control. Once a week, bait must be checked and restocked.Weeds are kept well mowed.

  • For manure disposal, the studs use dedicated pumps so that none of the manure handling equipment of contract haulers enters any buildings. Manure gravity-flows out of 2-ft.-deep, pull-plug pit systems to a concrete basin, where it is pumped out every 12 months and knived into adjacent ground using a dragline hose system.

Boar studs must follow a weekly checklist that includes a review of biosecurity procedures and environmental conditions inside the studs, concludes Groth.