Vaccine, Management Team Up to Wipe Out PRRS

A 1,150-sow gilt multiplier farm finally gained freedom from porcine reproductive and respiratory syndrome (PRRS) virus in 2002, after finishing a rollout of PRRS-vaccinated sows, thus completing a six-year effort to control and eradicate the virus. Belstra Milling Company's PIC gilt multiplication farm, Iroquois Valley Swine Breeders (IVSB), achieved PRRS-nave status using a conservative vaccination

A 1,150-sow gilt multiplier farm finally gained freedom from porcine reproductive and respiratory syndrome (PRRS) virus in 2002, after finishing a rollout of PRRS-vaccinated sows, thus completing a six-year effort to control and eradicate the virus.

Belstra Milling Company's PIC gilt multiplication farm, Iroquois Valley Swine Breeders (IVSB), achieved PRRS-naïve status using a conservative vaccination and management approach that enabled staff to finally walk the persistent virus off the single-site, farrow-to-finish operation at Fair Oaks, IN.

PRRS naïve is the ultimate health status for an animal population. It means that the group has never been exposed to the PRRS virus and there has been no detectable antibody or virus.

IVSB swine consulting veterinarian Tom Gillespie stresses that a multiplier unit that was once positive to a field and/or vaccine virus can become PRRS naïve once all exposed animals have been removed from the herd.

In contrast, PRRS-negative status means an animal is produced in a PRRS-positive system. However, virus exposure cannot be detected after maternal antibodies from the sow have waned.

What's been impressive at IVSB is that the farm has succeeded in staying PRRS naïve for nearly three years, observes Gillespie, owner of Rensselaer (IN) Swine Services.

“Vaccination ended nearly five years ago now, and Iroquois Valley has been producing negative offspring for about five years as well,” he adds.

Production Results

Production confirms what PRRS test results have indicated, according to Belstra Milling Production Strategy Coordinator Jon Hoek. Live pigs/sow/year has skyrocketed from around 22 during the time of the PRRS break in 1996 to an amazing 27.5 for 2003.

Reproductive problems have been minimal from PRRS infection a few years ago, and the operation has managed to keep the farrowing rate in the mid-to-upper 80s (Figure 1). Liveborn average is about 12.5 (Figure 2), with over an 11 weaned pig average (Figure 3). Stillborns and mummies have dropped from about 8% down to 5%. Wean-to-market losses are running at a respectable 4.5%, says Hoek.

PRRS Break

Gillespie says IVSB was in business five years when it suffered a moderate PRRS break in 1996. At that time, the gilt multiplier still mated females naturally and purchased semen from an outside source.

“We got on it pretty quickly because we are bleeding here monthly. We caught it in the finisher, identified that there was seroconversion (development of antibodies which reflect exposure to a disease pathogen) in the late nursery, and immediately started a PRRS sow vaccination program,” he explains.

Gillespie's basic PRRS control strategy is fairly straightforward. “We work to control all virus activity, monitor to ensure the sow herd is stable and that negative piglets are being weaned, and then we develop an additional strategy to handle nursery and finisher populations to achieve control or elimination.”

To work toward virus control, a PRRS vaccine was used in the sow herd from 1996 until 1999, when a formal control program, using Boehringer Ingelheim's first modified-live-virus (MLV) PRRS vaccine, began. Gillespie quickly learned that two doses of vaccine were necessary for protection. “Two doses far exceed the results with one dose; it is an amazing thing that we had to learn the hard way,” he says. Vaccination was given at 60 days of gestation and six days postfarrowing or postweaning. It was later determined that two doses approximately four weeks apart will work even better to begin control of virus activity.

In March 2000, Gillespie and Belstra Milling agreed it was time to mass-vaccinate sows. The sows were vaccinated twice, four weeks apart, “to provide stability and get everybody on the same playing field.” Sow vaccination ended permanently in June 2000.

During this process, naïve replacement gilts to be used as sentinel animals were placed directly into breeding and gestation to monitor any virus activity in the sow population, adds Gillespie.

“By June 2000, we knew we were weaning negative pigs at 19 days of age, but there was seroconversion in the late nursery. We wanted to stabilize the grow-finish portion of the site, so we closed the finishers to entry by doing a nursery depopulation,” explains Gillespie.

“We needed to create that bubble in the nurseries,” adds farm manager Kurt Nagel. Staff placed some of the 2,400 nursery pigs in the existing five finisher buildings and moved the remainder off-site.

Then, compromised, younger finishers were vaccinated twice for PRRS. The oldest were headed to market and didn't need to be vaccinated, because a 21-day withdrawal period must be observed for MLV PRRS vaccines, explains Gillespie.

Also, manager Nagel quarantined the finishers. “Even though we are single site, we tried to make the finishers as much a separate site at that point as we could. We designated people who went down that way, and they wore separate boots and coveralls and washed their hands,” he explains.

Gillespie recalls: “After the nursery depopulation of eight weeks, using unidirectional (one-way) animal flow, unvaccinated pigs flowed into finishing sites. This allowed us to keep an empty finisher between mass-vaccinated and negative pigs. We walked the vaccinated pigs off to market without contaminating the unvaccinated pigs that followed them.”

Gillespie says needles were changed with every pen in finishing. Also, the practice of moving finishing pigs between rooms to equalize size was stopped.

Other biosecurity practices are always strictly enforced, including shower-in, shower-out and rigid fly and rodent control programs. Boot dip use is enforced for entry to, and exit from, each room, and a spray hose just inside each room must be used to wash off boots to reduce the chance of disease spread, says Nagel.

Monitoring Program

Since finishers were cleaned up in 2000, there has been no recorded PRRS activity detected in any sow or pig populations at Iroquois Valley, stresses Gillespie.

Proof of that, and equally as important as the vaccine and management steps taken, is the monthly monitoring program, he emphasizes. The random sampling effort consists of blood testing 50 finishing pigs (10 pigs/barn, five barns) and 59 sows from the two breeding and gestating barns.

Rolling to Naïve Status

Vaccine virus persists in sows previously vaccinated. These sows were tested and removed, basically rolling them out of the system at the herd's 50% replacement rate, over a two-year period ending in 2002, says Belstra's Hoek. They have been replaced with non-vaccinated, naïve gilts.

Gillespie points out that it is important for a gilt supplier to produce naïve females for sale. So the thought of continuing to protect animals via vaccination became a moot issue at IVSB, which is sited in a low-dense hog area in northwestern Indiana.

However, if hog density is a big concern, and you are a commercial producer, continuing to use an MLV PRRS vaccine may be a wise choice, notes Gillespie.

“A lot of commercial units are happy to continue to vaccinate sows to control the field virus, wean negative pigs and then monitor the grow-finish population,” he concludes.

Since its discovery more than two decades ago, porcine reproductive and respiratory syndrome (PRRS) has certainly claimed the title as one of the most devastating swine diseases in U.S. history.

PRRS virus has produced catastrophic losses in all types and sizes of hog operations, confounding industry experts' attempts to control its spread. The ongoing challenge to subdue the disease has producers turning to a variety of control measures, some conventional and some controversial.

In the opening article of this series on PRRS control, an Indiana producer and his veterinarian used a conservative vaccination (modified-live-virus) and management approach to successfully walk the virus off a gilt multiplier farm.

In the second article, another Indiana producer and his veterinarian developed a five-year plan using a killed PRRS virus vaccine, moving a 600-sow gilt multiplier closer to PRRS eradication.

A trio of veterinarians in southern Minnesota discuss their experiences with serum therapy, a controversial, new approach to PRRS control.

Finally, a Kansas swine veterinarian has devised a closed herd procedure to phase out PRRS, emphasizing the development of natural immunity following infection, and forgoing the use of vaccines and medications.

Farrowing House Management

Since porcine reproductive and respiratory syndrome (PRRS) was tamed at Iroquois Valley Swine Breeders (IVSB) a few years back, farrowing house management has optimized output, says Jon Hoek, Production Strategy coordinator, Belstra Milling Company, Inc., DeMotte, IN.

At the center of that management strategy is colostrum consumption. “When you have a 12.5-pig born alive average, you are not going to wean all of those pigs, so we have ways of moving pigs around and saving piglets,” he says. Results have been encouraging: The weaning average is over 11, and in the last two years alone, preweaning mortality has dropped from 16% to 10-12%.

An overriding theme is the 95% “litter disruptive rate,” says Hoek. That means that 95% of litters are moved from their original mother. “Who the sow is or where the pigs go is not important — the pigs just go as needed,” he explains.

Key techniques are:

  • Using pig boxes

    These plastic boxes are placed in the farrowing crate during the first 10-12 hours after birth. At IVSB, all of the newborn pigs will stay in the boxes for a couple of hours to get dry and warm. Rice hulls and the drying agent Mistral are used to get the job done. “This is standard operating procedure and works well on all our farms,” says Hoek.

    Some of the other farms in the Belstra system use the pig boxes for other purposes. One use is to place half of the bigger pigs in the pig boxes during the first 12 hours of life to allow the 2.5-lb. and smaller pigs to obtain adequate colostrum.

  • Crossfostering

    Iroquois Valley farm manager Kurt Nagel tries to limit this practice to within the same rooms of about the same age piglets. He says the best sow for compromised pigs is often in the lower parities: a smaller sow with a good reproductive history, an even underline and smaller teats that smaller pigs can suckle.

    “A lot of times, we will take five pigs starving out in one room, and six starveouts in another room, and put them on the same sow,” says Nagel. “Pigs starving out don't have to fight a healthy pig to find a nipple; they are fighting with someone their own size, and therefore have a much better chance (of survival). Lots of times, a good nursing sow will wean about all of these pigs and they will be just as healthy and the same size as their contemporaries.”

  • Split nursing

    Pulling the biggest pigs off a top-milking sow allows the bottom two-thirds of a litter to access colostrum within the first few hours after birth, which is critical to success. “This gives even the squeakers in a large litter the opportunity to survive,” says Hoek.

  • Bump nursing/bump weaning

    Healthy pig-lets are sometimes weaned early so another group of pigs can be nursed by top sows, often resulting in these sows weaning double litters.

Milk replacer and watering cups with electrolytes are also provided pigs that are falling behind the rest of the litter, says Nagel.

To achieve these results takes more manpower. Hoek says one person to 90-100 sows is the standard ratio for the Iroquois Valley farm.

But this intensive management program makes producers more money and allows them to treat pigs as individuals, he observes.

Establishing sow herd stability to major pathogens like PRRS allows sows to perform to their genetic potential, and shows what the modern sow can achieve if managed properly, remarks Gillespie.