Strategic tool for a PRRS-free Denmark

Project overview

Project Start Date:  January 2026

The objectives of the project: 

  • Identify farm characteristics distinguishing compliant from non-compliant PRRS farms.
  • Analyze financial costs of non-compliance and intervention measures to support economic decision-making.
  • Evaluate PRRS detection timelines in disease-free areas to assess spread risks.
  • Enhance the national PRRS model with compliance, economic, and detection data for tailored, cost-effective interventions at municipality level.

Expected Publication of Project Results 

  • Report: December 2026
  • Scientific publications: September 2026

Publication of Results 

The project results will be published on this website under the section "Results and publications from the project". 

Project results

The results from the project will be published continuously on this page, no later than the end of 2026. The project results will be made available free of charge to all companies active in the sector or sub-sector in question.

Purpose

This study aims to update Denmark’s PRRS model at the municipality level to reflect new regulations, assess local variation, predict spread, estimate detection time in PRRS-free zones, evaluate cost-effective control strategies, and analyze the economic and epidemiological impact of farmer compliance and non-compliance—supporting efforts to eradicate PRRS and protect the pig industry.

Background

Porcine Reproductive and Respiratory Syndrome (PRRS) has impacted Denmark for over 30 years, with estimated annual losses of €4–€139 per sow (Rathkjen & Dall, 2017). Beyond economic costs, PRRS increases antibiotic use in affected herds. The Specific Pathogen Free (SPF) program, launched in 1993, aimed to control PRRS through herd testing, classification, strict biosecurity and movement rules (Fertner et al., 2025; SPF, 2024). As participation is voluntary, PRRS remains prevalent—about 35% of herds were infected in 2020 (Kristensen et al., 2020; Sundhedsstyringen, 2020).

To strengthen efforts, a national PRRS control plan was introduced in May 2022, requiring all herds to report PRRS status (Danish Ministry of Food, Agriculture and Fisheries, 2023). This reduced national prevalence to 22%. Under the current legislation, farmers can still choose whether to eradicate PRRS but purchasing pigs from infected herds will always result in a loss of PRRS-free status—discouraging risky purchases. In Denmark, based on available surveillance data on 2020/2021, 80% of sampled farms complied with the PRRS rule to avoid buying pigs from infected herds, but 20% did not, and contributing to further spread (Chang et al., 2025).

To better understand PRRS dynamics and evaluate control strategies, the University of Copenhagen, SEGES, and the Danish Agriculture & Food Council developed a national PRRS transmission model. Based on pre-2022/2023 data, the model revealed that 17% of undetected herds caused over 60% of new infections. Pig movements were the main transmission route for weaner herds. In sow herds, local transmission—via air, shared equipment, or personnel—within 5 km accounted for 60–70% of new infections. These findings align with U.S. data (Galvis et al., 2022a, b). However, the importance of each transmission route and to maintain PRRS free herds can vary depending on e.g., how farms are managed and whether farms follow the PRRS control guidelines.

The current model operates at the national scale, helping assess the impact of different transmission routes and interventions at the national level. As of January 2026, a new regulation is expected to be implemented that introduces the concept of “PRRS-free municipalities” - Criteria include: all herds must be PRRS-negative, a 5 km buffer zone around positive herds must be maintained for at least three months, and serological tests must be negative and recent. Surveillance will be required: annually in PRRS-free areas and biannually elsewhere including potential sanctions for PRRS-positive pig movements into PRRS-free zones and/or poor biosecurity (in alignment to Regulation EU 2016/429 (so-called “Animal Health Law—AHL”)). A second regulation, expected mid-2026, will require PCR testing of all seropositive herds sending pigs to slaughter and a positive PCR result will trigger a price deduction.

To support Denmark’s strengthened PRRS control efforts, it is essential to update the national PRRS model to reflect the upcoming regulatory framework. The revised model should work at the municipality level and reflect local variation, including PRRS-free status, pig and farm densities, production types, farmer compliance, transmission routes, and strategies like testing frequency. It must also consider economic impacts—such as price cuts for slaughter pigs from infected herds—and costs tied to non-compliance with movement and quarantine rules, all of which affect the pig industry.

This new regulation-aware PRRS model will support the identification of cost-effective, locally adapted strategies to control PRRS. It will also guide private industry and authorities in predicting the spread of infections, estimating detection times in PRRS-free areas, and assessing the potential impact of non-compliance. By encouraging farmer adherence to control measures and safeguarding PRRS-free municipalities, the model contributes directly to reducing infections and protecting Denmark’s pig industry.

References

  • Chang et al (2025): Modelling PRRS transmission between pig herds in Denmark and prediction of interventions impact. https://doi.org/10.1101/2025.05.09.653077
  • Danish Ministry of Food, Agriculture and Fisheries (2023): Executive Order on Porcine
  • Reproductive and Respiratory Disease (PRRS). https://www.retsinformation.dk/eli/lta/2023/997 
  • Fertner et al (2025): Indirect contacts between Danish pig farms–what are the frequencies and risk-reducing measures, and how can they be used in simulation models? Acta Veterinaria Scandinavica, 67(1), 7. 
  • Galvis et al (2022): Modelling and assessing additional transmission routes for porcine reproductive and respiratory syndrome virus: Vehicle movements and feed ingredients. https://doi.org/10.1111/tbed.14488 
  • Galvis et al (2022): Modelling the transmission and vaccination strategy for porcine reproductive and respiratory syndrome virus. https://doi.org/10.1111/tbed.14007 
  • Kristensen et al (2020): Production losses five months after outbreak with a recombinant of two PRRSV vaccine strains in 13 Danish sow herds. https://doi.org/10.1186/s40813-020-00165-z 
  • Rathkjen, P. H., Dall, J. (2017): Control and eradication of porcine reproductive and respiratory syndrome virus type 2 using a modified-live type 2 vaccine in combination with a load, close, homogenise model: An area elimination study. https://doi.org/10.1186/s13028-016-0270-z 
  • Regulation (EU) 2016/429: The European Parliament and of the Council of 9 March 2016 on transmissible animal diseases and amending and repealing certain acts in the area of animal health (‘Animal Health Law'). Available at: https://eur-lex.europa.eu/eli/reg/2016/429/oj/eng (Access on: 21 July 2025) 
  • SPF (2024): Specific Pathogen Free System. https://spfsus.dk/en 
  • Sundhedsstyringen (2020): The register of PRRS-infected swine herds in Denmark. 

Project activities

The activities will be implemented as work packages in the period 2026 in collaboration with SEGES and L&F.

Work Package 1 (WP1): Differentiation of herds regarding compliance with PRRS regulations (Jan–Apr 2026)
WP1 identifies herd-specific factors that influence compliance with PRRS regulations, focusing on pig movements and quarantine practices. Since 30% of farmers do not keep gilts in quarantine and 20% allow high-risk animal movements, a data-driven model will be used to profile compliant vs. non-compliant herds. The results will support targeted interventions and inform the PRRS model in WP4.

Work Package 2 (WP2): Cost analysis of non-compliance with PRRS and intervention measures (Feb–May 2026)
WP2 will quantify the economic consequences of non-compliance, including price deductions on slaughter pigs from infected herds and the costs of control measures. In addition, the economic benefits of full compliance will be estimated, providing a basis for improved adherence and political decision-making support. These economic insights will directly contribute to WP4’s assessment of control strategies.

Work Package 3 (WP3): Detection time for PRRS in free zones (Apr–Jul 2026)
WP3 focuses on the detection time for PRRS in PRRS-free municipalities and the likely extent of virus spread at the time of first detection. By simulating surveillance outcomes under both current protocols and the new regulation effective from January 2026, this WP will help improve strategies for protecting PRRS-free zones.

Work Package 4 (WP4): PRRS transmission and control at the municipal level (May–Dec 2026)
WP4 develops a PRRS transmission and control model at the municipal level, integrating key findings from WP1–3. The model will evaluate the effectiveness and cost-effectiveness of various locally adapted control strategies across municipalities, with the aim of supporting faster outbreak responses, reduced spread, and evidence-based policy development.

The project's expected effects

With the project's new tools, the Danish pig sector will be well equipped to investigate transmission routes, detection times, and cost-effective control strategies—thereby strengthening its ability to limit the spread and impact of PRRS, reduce economic losses, and protect PRRS-free areas.

Results and publications from the project

2026

Competence of resource persons

Professor Beate Conrady is the research group leader of “Infectious Disease Epidemiology and Animal Health Economics” (TIPTON Group) at the University of Copenhagen. 

She has extensive experience with infectious disease models in Danish pigs and cattle and maintains strong international collaborations in research applied to disease surveillance and control. She has established the animal health economics research at IVH, a modelling center for foot-and-mouth disease and other diseases in collaboration with the FAO and the European Commission. More information about her research results and profile can be found here. 

Dr. You Chang is a postdoctoral researcher in Beate Conrady’s research group, specializing in models for infectious diseases. She has more than 6 years of experience in mathematical modelling and statistical analysis, as well as in providing recommendations for disease prevention and control for livestock industry and public veterinary authorities. Her research profile can be found here

Dr. Philip Rasmussen is an assistant professor in Beate Conrady’s research group. His research focuses on livestock diseases with an emphasis on promoting evidence-based animal health policy through estimating economic burdens and costs and benefits of disease control strategies. His research profile can be found here: https://researchprofiles.ku.dk/en/persons/philip-rasmussen/

There will be close collaboration between the University of Copenhagen, SEGES Innovation and Landbrug & Fødevarer regarding the development of the model and the exchange of data.

Project organization and management

The project is led by Prof. Beate Conrady, who serves as the daily manager of the research group carrying out the work. It will be conducted in close collaboration with Mette Fertner from SEGES Innovation, as well as Kristian Møller and Nicolai Weber—experts in PRRS and the relevant Danish legislation—and Nils Toft, an expert in data science and modeling, all from Landbrug & Fødevarer (L&F). This collaboration ensures that the work is relevant, well-understood, and useful for stakeholders. All parties have extensive experience with legislations, PRRS control and PRRS-related databases, including data on animal movements, diagnostics, and SPF-status.

Financing

The project is financed by the Pig Levy Fund 2026. Total budget for the entire project (including overhead and excluding VAT) is 725 000 DKK.