When it comes to porcine reproductive and respiratory syndrome (PRRS), every producer wants to know what’s working and what’s not. Unfortunately, the fight against PRRS is not that easy as new strains continue to affect pork production in the U.S. and around the world.
Two strains getting more attention lately include PRRS virus L1C variant of RFLP 1-4-4 and PRRS virus L1C 1-2-4 in the U.S., and Rosalia, a PRRSV-1 strain with increased virulence affecting swine production in Spain.
During a webinar hosted by the Swine Health Information Center (SHIC) and the American Association of Swine Veterinarians (AASV), Enric Mateu, Autonomous University of Barcelona (Spain); Daniel Linhares, DVM, and Giovani Trevisan, DVM, Iowa State University; Paul Yeske, DVM, Swine Vet Center, and Clayton Johnson, DVM, Carthage Veterinary Service discussed a variety of topics from Rosalia’s significant impact on swine production in Spain to on-farm experience with prevention and controls measures for PRRSV L1C variant, SHIC reported in its recent newsletter.
Consequences of Rosalia in Spain
In Spain, 18 million pigs have been impacted by Rosalia, a devastating strain of PRRS that results in abortion storms in sow herds, sow mortality, stillbirths, high mortality in suckling piglets and weaners, and decreased feed conversion rates. Mateu said on average, the most affected farms lost 15% to 20% of their annual income.
For perspective, there are 34 million pigs total in Spain and 146 million in the European Union. The primary area impacted spans 31,000 square miles in the northeast quadrant of the country. In the area of greatest prevalence, 1,000 sow farms, averaging 1,400 sows each, are present. Further, 490 farms with nursery operations exist in that area of viral circulation and 8,000 farms where pigs are finished. On sow farms, the PRRS vaccination rate is 70%, less than 20% of nursery farms are vaccinated, and less than 5% of finishing farms.
Although Spain is probably in a phase with decreasing impacts, Mateu said the industry remains vigilant in its efforts to combat Rosalia’s impact. Vaccination, McRebel (management changes to reduce exposure to bacteria to eliminate losses from PRRS), changing farrowing schedules and depopulation have all been implemented with varying results, he noted.
Concerning PRRS Strains in U.S.
Linhares and Trevisan discussed PRRS virus monitoring data from the Swine Disease Reporting System (SDRS), a SHIC-funded collaborative project among five veterinary diagnostic laboratories.
Using data collected from the five veterinary diagnostic labs participating in SDRS, Linhares and Trevisan shared PRRS virus evolution and genetic variability across states. Data included information on PRRS virus L1C RFLP 1-2-4. From 2009 to 2021, per SDRS, there were 421 detections of this strain. In 2022, there were 264 classifications.
This data shows PRRSV L1C variant is still an eminent animal health and production threat and is moving east, threatening 1.5 million or more sows in 2023. They emphasized biocontainment and biosecurity in eastern states to prevent introduction of that strain into pig populations at risk in that region.
SDRS monthly reports can be accessed on the SHIC website.
PRRS Outbreak Considerations
Yeske, a Minnesota-based practitioner, shared tips to consider during a PRRS outbreak and herd closure. He also addressed depopulation/repopulation strategies. When moving through the early days of a PRRS break, Yeske said abortions and farrowing sows with retained pigs are the most common cause of sow mortality. Assisting sows in this process, just as assisting with farrowing, is essential, he explained.
He also advised increasing breeding targets as much as possible, breeding back sows that aborted and identifying open sows as soon as possible. To save pigs, he recommended moving piglets as needed and treating them more aggressively.
Regarding herd stabilization, Yeske walked through three scenarios:
1. Allow herd to remain positive
2. Eliminate the field strain
3. Depopulation/repopulation
Yeske shared processes, recommendations and results as well as timelines. The overview addressed McRebel-like procedures and Yeske’s cautions regarding its implementation, diagnostic monitoring, and an early weaning strategy. Depopulation/repopulation as a tool to address PRRS breaks serves as a viable strategy in the U.S. production model, due to multi-site production, Yeske added.
He also stressed the need for bio-containment, or keeping the virus on the site, as equally essential to bio-exclusion, keeping the virus out. He added that bio-containment is the forgotten part of biosecurity, a process addressing showering out of barns and handling mortalities as well as disposal of boots and coveralls among other practices.
Real-Life Experience with PRRS
Johnson shared experience with PRRS virus breaks on three sow farms, each varying in intensity. He pointed out that biosecurity, understanding PRRS virus strain lineage and PRRS vaccination all have been effective tools for PRRS management.
However, herd closure, prevention of latent PRRS clinical resurgence, regional PRRS management programs, and grow/finish biosecurity are all opportunities that need attention. Questions surrounding the origin of PRRS virus strains lead to confusion as does knowing where the emerging strain will display virulence, and how isolate specific PRRS management strategies should be, he noted.
He believes the industry can benefit from more research.
“Each novel PRRS strain expresses virulence in a unique manner,” Johnson said. “Should the industry fund a working group whose focus is constantly working on the latest novel PRRS strain?”
Editor’s Note: Complete presentations, as well as attendee questions for speakers, are all included in the full webinar available on the SHIC website.
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