Attempts to clean up porcine reproductive and respiratory syndrome (PRRS) in the United States encountered some new breaks in 2006.

A year ago, the Carthage (IL) Veterinary Service, Ltd. (CVS) came close to achieving a milestone. The large sow system it services and manages in Illinois and Missouri nearly became PRRS-negative for the first time since the virus struck the region decades ago.

Keith Erlandson, DVM, in charge of PRRS control programs for CVS, says 95% of the system had achieved negative status when a number of disease breaks occurred earlier this year, mainly during the winter, when virus survival is much higher.

The CVS staff have not been able to figure out exactly how the breaks occurred, he says, except the follow-up blood testing of all farms revealed the reinfected herds came down with a new strain of the virus.

“For a lot of people around the country it has been a pretty bad year for PRRS,” says Erlandson. He estimates their sow system has now dropped to about 75% free of PRRS.

CVS's Joe Connor, DVM, says the movement of the PRRS virus this past winter into previously clean areas of the sow systems has caused particular frustration, raising questions about what additional steps may be needed to prevent introduction.

In the late 1990s, most PRRS breaks were linked to incomplete testing that resulted in PRRS-positive gilts entering the sow system. But those slipups have been easy to track down, whereas this latest series of breaks has proven to be a “big mystery,” he says.

Connor recalls a survey of biosecurity practices in the highly integrated poultry industry a few years ago. The survey revealed that even with intensive biosecurity efforts, lapses were discovered in videotapes of barn activity, and the failure rate of procedures was quite high.

For PRRS control, training of farm staff becomes critical to assure understanding and follow-through of biosecurity practices.

Connor points out that eliminating PRRS virus is different than ridding the industry of pseudorabies. “What we are missing is a vaccine that can reduce shedding, decrease the challenge dose in the virus, and a differential vaccine.” Animals vaccinated for pseudorabies could be differentiated from those infected by a field strain, he explains.

Sow Centers

Sow center units range from 2,600 up to a few with 6,400 sows. They are organized as limited liability companies, each owned by about two-dozen area producers and overseen by a board of directors.

Professional Swine Management, an arm of CVS, provides management services, including handling day-to-day operations, management of the gilt flow, accounting, bookkeeping and personnel issues.

In turn, producer-owners receive large groups of 21-day-old weaned pigs to finish out on their farms.

Cleanup Procedures

Of the sow farms that have broken with PRRS this year, one herd was depopulated and four are in the process of being rolled over, says Erlandson. Depopulations are very costly, but can still be the right decision if the disease load is high enough, causing production to suffer.

Success rate is running about 90% on rollovers. Since the capital investment is small, if the herd breaks again, it's worth it to simply start the process over, he says. A rollover takes at least two years and plenty of patience to complete, says Erlandson.

A PRRS break at a Carthage-managed sow center serves as an example of how a PRRS rollover works.

“The sow center was a PRRS-naïve population to start with, when the PRRS virus got introduced about eight weeks into breeding,” he recalls. Veterinary staff collected serum from sows and older pigs to use for serum therapy. All animals on the farm were then “mass-inoculated” with serum containing the PRRS virus.

Every pig down to the youngest replacement gilt (21 days old) was inoculated with virus to make the whole herd positive for PRRS at the same time to create herd stability, says Erlandson.

The farm was able to continue in production, uninterrupted, unlike a depopulation where everything is shut down. No gilt replacements were introduced for six months. Replacement is targeted at 50% annually.

To resume gilt introductions, naïve gilt replacements raised in rented, off-site finishers were brought in, en masse. Gilts in all phases — from the youngest weaners all the way up to mature gilts — were introduced at the same time, he explains.

“When we start rolling in naïve gilts, we treat the farm as having two populations: a positive population and a negative population,” explains Erlandson. “We will go so far as making sure that a negative (naïve) gilt never shares a water trough with a positive animal, although flow may dictate that. They are right across the alley, but they never share a water trough.

“And when farm staff goes out to treat, they carry a positive treatment kit and a negative treatment kit, so there is no chance that a negative animal is going to be ‘shot’ with a needle that was just in a PRRS-positive animal,” he says.

At farrowing, known PRRS-positive and PRRS-negative populations were kept segregated. No crossfostering was allowed between the two groups. For accurate identification, all positive sows were identified with a commercial paint marker. Gestating sows of different PRRS health status were also kept physically separated.

About a year ago, some two years after the control program started, the last PRRS-positive sow was rolled out of the sow center. “The negative sows, while they may have been housed throughout the cleanup effort in the same barn as the positive sows, never came down with the virus,” observes Erlandson.

Serum Therapy Do's and Don'ts

Serum therapy shouldn't be tried without the consultation and direct involvement of a veterinarian, cautions Erlandson.

Take action quickly after a PRRS diagnosis has been confirmed. “Serum therapy can be a useful tool, but it has a fairly limited scope of usefulness, and should be considered as a targeted approach to a specific problem,” he says.

If a herd is already positive for PRRS, and another strain of the virus gets introduced, extra time will be required to identify the new strain.

“I think this process works best when there is just a single introduction into a naïve or negative herd,” stresses Erlandson.

Secondary Invaders

Secondary invaders complicate the PRRS challenge. Swine influenza virus (SIV) and Mycoplasmal pneumonia are the chief issues, but porcine circovirus-associated disease is also starting to create problems in PRRS-infected herds, says Erlandson.

Gilts, especially, should be targeted for mycoplasma vaccination as early as 21 days old (when they are selected as replacements), with a booster shot three weeks later. Sows should be vaccinated before farrowing. Weaned pigs should receive a one-shot mycoplasma vaccine during that first week of arrival at a producer's farm.

It's known that sows can shed the PRRS virus for quite a long time. If SIV strikes, it decreases immunity and can prolong PRRS shedding. CVS mass-vaccinates sows seasonally for SIV, except for summer. This approach provides consistently high maternal antibodies and protection in sows and also provides strong protection for piglets, vs. a prefarrow vaccination program that only protects 5% of the sow herd at a time. The proof of success is the fact that the sow centers have gone three years without a flu break.

CVS also advises employees to be vaccinated against influenza, thus providing protection from infection for both people and pigs, says Erlandson.

Biosecurity

Transportation biosecurity is key in a sow system that sends out large numbers of weaned pigs to its owners every week.

“We insist that the loadouts at the receiving farms be washed and disinfected prior to arrival, or that the producers use designated pig trailers,” says Erlandson.

The sow system is also building a two-bay truck wash and drying bay that is being paid for by producer-owners. “That is going to give us a lot more confidence in the area of pig transportation,” he says.

Producer sow center owners are limited to visiting sow farms once or twice a year. “We understand that the owners have made a significant investment in the sow herd, and want to check up on it, but we try to limit the visitors to the sites,” says Erlandson.

Meetings with farm employees and truckers are frequently held to emphasize biosecurity protocols and the importance of downtime.

Sow Center Owner Enjoys PRRS Freedom

Randy Scheetz of Burnside, IL, has raised hogs since 1970. For about half that time, he has struggled with the porcine reproductive and respiratory syndrome (PRRS) virus as a farrow-to-finish producer and later as a feeder pig finisher.

But as a shareholder in three sow centers managed by Carthage Veterinary Service, Ltd., he has enjoyed freedom from PRRS for four years. He finishes out feeder pigs from two of the sow centers. The third sow center, near his home, delivers 21-day-old pigs for finishing in two, 1,200-head, wean-to-finish barns.

PRRS freedom allows Scheetz to keep costs down in those wean-to-finish barns in several ways:

  • No vaccinations from the time the 15-pounders arrive at his farm until they head to market at about 300 lb.

  • Pigs are medicated with chlortetracycline and tiamulin in the starter feed for about three weeks to control staph and strep infections. Pigs are also given aureomycin as a water-pulse medication, usually during that first week to control mycoplasma.

  • Pigs are overpopulated in the wean-to-finish barns. When groups arrive, Scheetz stocks 45 head/pen, using the buildings as nurseries until pigs reach about 100 lb. Then 15 head are pulled out of each pen and moved to a 450-head, off-site finisher, leaving 30 head/pen in the wean-to-finish barns.

    “I can utilize this space as a nursery and utilize my wean-to-finish barns more efficiently by filling it an extra one-third full, and it is not costing me a dime in extra facilities,” explains Scheetz.

    During this stress period of moving and sorting, pigs sometimes develop a cough. If caught on the first day, they can be successfully treated for mycoplasma using chlortetracycline, he says. These pigs will be treated for three to five days.

  • Pigs will be treated for ileitis with tylosin for the last two weeks or so of their finishing period.

“Randy is a producer who really understands the disease dynamics that goes on in his farms, and we have worked with him to develop a targeted medication strategy to take care of these problems before they really crop up,” says his veterinarian, Keith Erlandson.

Eliminating PRRS and switching to a gruel feed if pigs start stalling have both worked to nearly eliminate fallback pigs. Culls/death loss combined range in a respectable 3-6% of finishing pigs.

Filling barns in seven days or less with healthier pigs has reduced sorting to once during finishing, remarks Scheetz. Only a handful won't reach market weight, he says, and those tail-enders are fed out in a Cargill-style finisher.

PRRS-negative sows lead to PRRS-free pigs and Scheetz says even on a cheap feed that he uses to capture higher returns, the 21-day-old pigs reach 300-lb. finishing weight in five months. They are marketed at around six months of age.

Erlandson says Scheetz' decision not to overcrowd pigs is another big factor in keeping down disease levels in his wean-to-finish barns.

“Instead of feeding out 2,400 pigs, which he is entitled to get at a time, he has chosen to feed out 1,800 head in the wean-to-finish barns and sell the remainder as feeder pigs,” he says.

Alternative Vaccine Produced for PRRS

MJ Biologics has utilized a new, breakthrough process to capture the viral components necessary to produce a viable, alternative vaccine to combat porcine reproductive and respiratory syndrome (PRRS).

The Mankato, MN-based company's autogenous (custom) vaccine is produced using the Selectigen MJPRRS Technology, a new, patent-pending method in viral manipulation and subunit vaccine manufacturing.

The process selectively collects and concentrates viral antigens that were formerly trapped inside the structure of a killed virus, allowing for greater antigenic mass in production of the vaccine.

Unlike traditional PRRS vaccine production, where viral cells are harvested after complete release from the host cell, Selectigen MJPRRS Technology harvests cells at a point in time during incubation that concentrates relatively high viral antigen components in a free form.

The intricate process of extraction requires several extra steps beyond the production of traditional vaccines to dramatically increase viral antigen concentration in the final product.

The vaccine production process was invented by Han Soo Joo, University of Minnesota, and is exclusively licensed by the University of Minnesota.

For more information on the Selectigen MJPRRS Technology and other autogenous biologics, contact MJ Biologics at (507) 385-0299 or go to www.mjbio.com. For sales information, contact distributor Newport Laboratories of Worthington, MN, at (800) 220-2522 or go to www.newportlabs.com.