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First County PRRS Control Program Advances

Rice County, MN, is the first known county to attempt a PRRS (porcine reproductive and respiratory syndrome) control program. The Minnesota county, less than an hour's drive south of the Twin Cities, is nearly perfect for testing a partial county PRRS control effort, says Mike Strobel, DVM, Northfield, MN. In that regard, the area is kind of an island unto itself and a good candidate to test whether

Rice County, MN, is the first known county to attempt a PRRS (porcine reproductive and respiratory syndrome) control program.

The Minnesota county, less than an hour's drive south of the Twin Cities, is nearly perfect for testing a partial county PRRS control effort, says Mike Strobel, DVM, Northfield, MN.

In that regard, the area is kind of an “island unto itself and a good candidate to test whether PRRS can be stabilized and ultimately eliminated from an area,” he adds.

The project encompasses 30 producers with pigs on 49 sites in eastern Rice County, an area bordered on the north by Twin City suburbs, on the west by Interstate Highway 35 and with sparse pig numbers to the south and east.

Strobel and Minnesota swine veterinarians Roger Green of Faribault; Tom Lang of Clarks Grove; and Denny Rossiter and Paul Yeske, both of St. Peter, are collaborating with University of Minnesota swine veterinarians Robert Morrison and Enrique Mondaca on the two-year-old project.

Testing Results

To date, about 90% of the herds have been tested for PRRS and infected operations identified. Producers can now sign onto a password-protected Web site to locate infected herds in the project area. Strobel says the site only identifies whether herds are positive or negative and their location, and does not actually identify the operation by producer name. Producers must sign non-disclosure agreements to participate.

Only a few farms have refused to participate. The project includes a handful of large sow farms, several smaller farrow-to-finish operations and a number of nursery and finishing operations.

Even though testing results are still preliminary, Strobel says it is already apparent that PRRS control in an area is possible.

“I really think we have enough strategies today to control the virus regionally. In order to be successful, you just have to have everybody willing to cooperate and work toward the same goals. I think in Rice County we are probably a year away from completely reaching that reality.”

Strobel lists a couple of key points to project success borne out by the testing:

  • There appears to be a very low incidence of disease spread between neighbors, even though some of the sites are only a quarter of a mile apart.

  • Aerosol spread does not appear to be as common as previously thought. “It's not like pseudorabies, where if your neighbor had it, there is a pretty good chance you are going to get it because it spreads through the air very readily,” he comments.

Testing has revealed there are 10-12 PRRS virus strains in eastern Rice County. Farms tend to have the same, single strain throughout their operation. Strains have not been shown to drift from one farm to another, he says.

Strobel says project testing has shown that 95% of the PRRS breaks are not due to aerosol spread of the virus, but rather to biosecurity breakdowns due to people or animal movement.

Trucking is a huge biosecurity factor, probably bigger than we ever thought, Strobel comments. “It is a major contributor to the spread of PRRS between sites. If you don't do the right things, you will have problems.

“The solutions are simple — washing, cleaning and drying. Drying is probably the most important thing,” he emphasizes.

Producer Benefits

Producers have benefited directly from the project in learning the true value of biosecurity in protecting their herds from PRRS, says Strobel.

They have also learned the value of working closer with their swine veterinarian in developing a herd health program. He projects PRRS infection can cost a producer $5-7/pig. The cost of full-service veterinary care is less than 20¢/pig.

PRRS Control Measures

Producers are learning that it's unwise to totally clean up (depopulate/repopulate) their herds in an area where there are a number of other hog operations, according to Strobel.

The goal today is to immunize the sow herd to produce negative piglets — an effort that has been working well, he suggests. The most common strategy is gilt immunization using a variety of exposure and vaccination programs.

Ultimately, once the vast majority of producers have cooperated, disease prevalence can be decreased, adds Morrison. As disease levels decline, PRRS-negative pigs can be safely imported into the region to be finished.

Testing for the Rice County PRRS project is being paid for with a combination of funds from the Minnesota Pork Producers Association and the National Pork Board, says Morrison.

Plans for a second PRRS control project in Stevens County, MN, calls for testing to be funded by producers, states Morrison. Stevens County is located in west central Minnesota, and is home to several large breeding stock companies.

Total Farms in the Area 49
Participating Farms 44 (44%)1
Tested Farms 41 (93%)2
PRRSV ELISA (+) 35 (80%)2
PRRSV PCR (+) 13 (30%)2
1Percentage of the total number of farms in the area
2Percentage of the number of participating farms

Is PRRS Vaccination Just For Sows?

Though control strategies for managing porcine reproductive and respiratory syndrome (PRRS) vary widely, most focus on protecting the top of the pyramid, notably the sow farm.

Most producers getting PRRS-negative pigs believe sow vaccination is the best investment.

But stabilizing the sow herd isn't always enough. Some grow-finish operations must commingle pigs from different sow herds, some of which may not be PRRS-stable.

PRRS Challenges

North Carolina farmers face that challenge.

“You would be hard-pressed to find a PRRS-negative finishing floor in eastern North Carolina,” says Randy Jones, DVM, Livestock Veterinary Services, Kinston, NC. “We face significant, vertical spread of the PRRS virus.”

The answer for Jones and others has been to vaccinate pigs before exposure to the virus.

“As with any vaccine, the key to success is to vaccinate far enough ahead to develop immunity,” says Jones. “Where we have exposure to PRRS in finishing, we try to vaccinate two to four weeks prior to exposure.

“In some cases, with field virus circulation and exposure in the nursery, vaccination needs to occur as early as 7 days of age,” he adds.

If the sow farms are stabilized, or if growing pigs are from a single, PRRS-stable source, pigs aren't vaccinated for PRRS, he says.

PRRS Strategy

Phil Ruch, owner of Pork Place Farms, Lincoln, IL, stabilized his sow farm with quarterly vaccinations and a stringent gilt replacement vaccination program.

But problems persisted. Weaned, PRRS-negative pigs were being exposed to the virus in the nursery in spite of all-in, all-out production.

When pigs entered the continuous-flow grower, it only made matters worse. Older pigs shed virus to younger, naive pigs, resulting in respiratory disease and production losses.

“My pigs were going through a cycle of good health, then became infected with PRRS and developed respiratory problems. The end result would be high morbidity,” says Ruch. “I had done the serology testing and knew pigs were getting infected postweaning.”

He vaccinated all pigs with a PRRS modified-live-virus vaccine (MLV) at 3 weeks of age and controlled the virus in growing pigs. Vaccination has decreased the virus load and reproductive disease it causes in the breeding herd. Vaccination also reduced the respiratory form of PRRS in growing pigs.

“Up to this point, I have never seen the genetic potential of my herd expressed in my finishing hogs,” says Ruch. “The price of vaccination is a small price to pay for improved overall health.”

Vaccination Investment

The National Pork Board and Iowa State University report PRRS adds from $5.60 to $7.60 per head sold to the cost of production.

“Each pig arriving at the finishing barn represents an investment already made,” says Reid Philips, DVM, senior technical manager, Boehringer Ingelheim Vetmedica, Inc., St. Joseph, MO. “By protecting that investment from negative performance caused by disease, continued economic return may be realized.”

Philips adds the benefits of vaccinating growing pigs for PRRS is derived from mortality reduction and improved average daily gain (ADG).

“If you estimate the vaccination and administration costs at $1/pig, then the breakeven point is a reduction in mortality of 1% and an increase in ADG of .05 lb.

“Using conservative industry figures when calculating net return on investment, if you are able to use a vaccine intervention that can reduce mortality by 3% and increase ADG by .15 lb., you can realize a net return on that investment between $5-6,” says Philips.