To clean up sow breed-to-wean herds when they turn positive for porcine reproductive and respiratory syndrome (PRRS) in the fall, the Pipestone (MN) Veterinary Clinic has developed best practices to be incorporated into a standard protocol for disease elimination in its production network. It’s called the Pipestone System.

The goal for each newly infected farm is to follow this protocol to eliminate the field virus, said Joel Nerem, DVM, Pipestone Veterinary Clinic (PVC).

“We still believe there are valid reasons to eliminate PRRS virus from sow farms due to the cost of disease, the cost of animal well-being and the impact on the farm staff taking care of these farms when they have to deal with ongoing PRRS infections,” he said in a talk at the Leman Swine Conference in mid-September in St. Paul, MN.

Nerem said PRRS has been successfully eliminated from infected breeding herds in the Pipestone System with a load-close-expose process using either modified-live-virus (MLV) vaccine or exposure to field virus (live virus inoculation).

“Our statement has been and is today that every farm is only about 250 days away from PRRS-free production,” he said.

If PRRS virus can be eliminated on sow farms and protected through high biosecurity measures, potentially including filtration, “then we can stop the dissemination of new PRRS virus strains by stopping the movement of PRRS-infected weaned pigs,” Nerem declared.

Elimination Principles

The two principles of the Pipestone plan include exposure of all breeding animals on the farm to the new PRRS virus to develop herd immunity, and cessation of new breeding stock introductions to put the virus fire out.

Each PVC sow herd elimination protocol must include:

● A written plan approved by the health director to include live-virus inoculation (LVI) or vaccine, decision on farm closure, when to bring in new gilts and when to test, all set out in a clear, written plan

● How whole-herd exposure will be accomplished: through serum exposure/LVI or mass vaccination with an (MLV) PRRS vaccine

“We do both LVI and MLV, but I would probably say we have seen a drift more toward MLV vaccination. But this is a decision that is made not just by the veterinarian, but by production leadership and the ownership,” Nerem stressed.

Following those steps, the gilt developer unit (GDU) is then loaded with up to a six-month supply of gilts that are protected via LVI. If the decision is to use vaccine in the exposure program, then the gilts will also receive two doses of MLV vaccine.

The project lasts 250 days — longer than the previous 200 days — to give it a better chance of success, Nerem said.

During the first 16 weeks of herd closure:

● The farm is closed to replacement gilt introductions.

● Virus exposure “homogenization” begins, which includes serum or vaccine and provides field virus exposure plus PRRS vaccine to non-pregnant gilts.

Of note is ending the practice of retaining vasectomized boars for heat detection during herd closure, due to concerns they may turn up viremic and infect naive gilts that are brought back onto the farm, Nerem said.

Serum samples are kept in storage that were used for gilt exposure for potential later analysis.

During weeks 17-36 of herd closure, there are 15 steps to follow in the PVC protocol:

1. Begin pig movement restrictions in farrowing, only sizing piglets, euthanizing viremic pigs and not holding pigs back at weaning.

2. Begin piglet testing no later than 16-18 weeks into closure using oral fluids and serum; make sure this serum leaves the farm before the end of the closure project and production of negative pigs, as this represents a high biosecurity risk.

3. Change needles and disinfect nippers between litters.

4. Stop partial washing of farrowing rooms.

5. Foam hallways with Synergize disinfectant (Preserve International) prior to power-washing following weaning events.

6. Eliminate the use of tubs or processing carts to stop the dissemination of the virus between litters.

7. Discontinue all pre-farrow feedback.

8. Discard all serum retained on the farm.

9. Discard all frozen/refrigerated feedback material retained on farm.

10. Defrost, clean and disinfect all farm refrigerators and freezers.

11. Defrost all open bottles, needles, syringes, oral dispensers, etc., from the refrigerator and the medicine storage area, as well as any open bottles or delivery devices that may have been used when animals were still viremic on the farm.

12. Clean and disinfect all storage areas, hallways, water rooms, etc., with a good, general farm cleaning.

13. Discontinue manure pumping or agitation within 14 days from the end of herd closure (arrival of naive gilts). In the Pipestone System, all manure pumping following herd closure must be approved by the health director. “We just want to make sure that we don’t have anyplace on the farm where the virus might be hanging around that once we reintroduce naive replacement gilts, that we are going to have a potential source of exposure,” Nerem explained.

14. Discontinue oral dosing of piglets.

15. The gilt developer unit must be cleaned, disinfected and inspected by the farm’s health technician. “Basically, we want to have a control in place where the farm veterinarian and the farm staff are not on their own in making this call. We have the director of health responsible for overseeing that all of the requirements have been met, that he and the farm veterinarian have signed off, and said they have done everything that they need to do to release this farm from elimination and to start bringing in new gilts,” he asserted.

Test Release From Herd Closure

PVC became a great deal more aggressive in its testing protocol in the last couple of years for release from herd closure. Three criteria are required:

1. Three bleeds of 30 head of pigs at two-week intervals must be 100% negative on polymerase chain reaction (PCR).

2. Three bleeds of 60 head of pigs at two-week intervals must be 100% PCR-negative.

3. Collect six ropes (12 litters) from oral fluid testing of piglets on the weeks opposite that of serum collection.

“Testing is aimed at pigs just prior to weaning — focusing on fallback pigs, small pigs or any pig that looks like it may have a health or growth issue compared to the general population of the farrowing house,” Nerem said.

The inherent requirement that must be met is the arbitrary timeline of 250 days, “before we basically sign off and say we believe that we have eliminated PRRS to the best of our ability and open the door to naive replacement gilts,” he reiterated.

Post-Closure Testing

Additional testing to assure freedom from PRRS virus includes monthly testing of weaned pigs using PCR, and monthly PRRS PCR testing of naive replacement gilts that have entered the gestation barn. About 10 head are bled for about six months.

By following the protocols, PVC has documented better than 90% success rate in eliminating PRRS virus from farms in the Pipestone System, Nerem said.