Swine respiratory disease (SRD) is the most common cause of morbidity and mortality in swine herds throughout the United States. 1 SRD’s primary contributor, porcine reproductive and respiratory syndrome virus (PRRSV), was identified more than three decades ago in the United States and results in estimated losses as high as $1.2 billion each year.2 Managing PRRS is an ongoing process as it is common for pigs to become infected with more than one strain of the virus in their lifetime.
An effective SRD control strategy considers the pathogen, host, and environment interactions that influence the occurrence and spread of disease. Further complicating things, veterinarians are constantly considering the susceptible, infected, or resistant host subpopulations for the variable bacterial and viral pathogens found in each environment at that time. Each pathogen, each host, and each environment are constantly changing, and therefore, plans need to change too. Even if the pathogen and host variables stay the same, the way pigs are raised in the summer or winter environments requires a different plan.
SRD cannot be addressed with a one-size-fits-all plan. Even for two piglets born in the same litter, the risk factors for each can be highly variable, ultimately affecting their lifetime productivity. For example, pig A was 3.0 pounds at birth – born first, not viremic for PRRS, and received adequate colostrum. Their littermate, pig B, was 1.5 pounds at birth – viremic for PRRS and was the 16th piglet in the litter to be born to the same sow that spent 10 hours farrowing and probably received inadequate colostrum. The challenge is figuring out the best way to manage these two very different “hosts” that come from the same litter until the weaning stage. Once in the weaning stage, the piglets will co-mingle with multiple litters from multiple farrowing rooms and possibly multiple farms. This scenario is not unique and happens every day.
The PRRS virus’ ability to rapidly shed, spread, evolve and become highly diverse makes controlling and eliminating the disease very challenging.3 For this reason, modern pig production has evolved into a very complicated process. Batch farrowing, all-in-all-out groups (AIAO), and 3-site production provide great advantages when trying to stop the vertical and lateral spread of disease from one group of pigs to another. However, it also creates disadvantages by adding more pig movements, more stress on pigs, more assets, more oversight, and more fomites that could potentially transfer the virus.
This article will explore best practices when working with your veterinarian to mitigate, manage and control SRD. There is always an entry point when PRRS makes its way into a herd, but a successful mitigation plan keeps most pathogens out. Therefore, it is key to work with your veterinarian to develop a robust defense plan unique to your operation and continually re-evaluate as pressures on pathogen, host, and environment change.
Develop a Layered Biosecurity Plan
PRRSV does not have legs or wings so for a pig to become infected, the virus needs to catch a ride on something. The primary purpose of a biosecurity plan is to protect swine health by preventing disease introduction and spread. Defense and management of PRRS, and other SRD pathogens, requires a comprehensive biosecurity plan properly executed every day. Good biosecurity plans have intentional processes detailing how all people, animals, supplies, etc. enter and exit a farm. Great biosecurity plans are layered so that if one process fails, another will catch it.
Risk = Impact × Probability
Risk is often calculated by multiplying the potential impact of a hazard by its probability. Therefore, biosecurity plans will naturally be focused on the pathogens with the highest impact (most costly) and the activities with the highest probability of infection. In addition, greater focus is directed toward the higher risk events you are doing most often. PRRSV is not only the costliest, but actions taken to prevent its spread also work for most other higher priority pathogens. For this reason, at a minimum, biosecurity protocols are methodically focused on routine activities with a higher risk score like animal and personnel movements, feed and supply delivery, and sharing equipment with another farm.
We must also try to do our best to manage the things that we have less control over, like location relative to other pigs. Studies have confirmed PRRSV detection in air samples up to 9.1 km (5.6 mi) from an infected source. 4 Aerosol transmission occurs via respiratory secretions or contaminated particles carried by wind or air currents making proximity to other pigs a top two risk factor. Since the location of a farm cannot be changed, focusing on biocontainment (keeping pathogens contained) in positive farms, and bioexclusion (keeping pathogens out) in negative farms like HEPA filtering and positive ventilation, become key.
It is important to recognize that a biosecurity plan is exclusive to each operation. Once you identify the most likely risks, developing a plan is relatively straight forward. The biggest challenge to a plan is everyone executing every day. Ask your veterinarian to audit the plan routinely, and if something in the plan can’t be executed, find another way.
Real-Time Monitoring
It is standard practice for producers to use web-based software to track key performance indicators (KPIs) to maximize operational profitability. Historically, that data wasn’t available until it was manually input into the software or until the barn closes out. Today, an increasingly popular practice is the utilization of precision farming technology to monitor environments and surveil health in real-time. We now have sensors and cameras feeding into AI systems that can not only predictively track animal activity, temperature, humidity, ventilation, air quality and CO2 levels, but also alert producers when an environmental or health event may occur.
Lethargy and anorexia are often the first noticeable clinical signs observed when pigs become sick, even before coughing begins. If pigs don’t feel like getting up, they don’t eat or drink. So, from a health-monitoring perspective, equipping real-time water disappearance meters can alert producers within the first 12 hours of an outbreak. This type of real-time data gives producers and veterinarians a head start on diagnostics and interventions that could dramatically reduce morbidity and mortality.
Routine Diagnostic Monitoring
Collecting a diagnostic sample like oral fluids and submitting it for testing is like watching 3 minutes of a movie. It only tells you the status of the pathogen you tested for at that place and time. You only start to see the big picture when you put enough 3-minute clips together, which is equivalent to routine diagnostic sampling.
The power of longitudinal or routine sampling primarily lies in early detection of subclinical infections particularly for pathogens like PRRSV that can be extremely variable in clinical signs. The traditional incidence rate during a PRRS break will start at 0% before the break, reach 100% sometime after, and then eventually decrease until it reaches 0% again as the population moves through the susceptible-infected-resistant epidemiology curve – barring the introduction of new animals and new strains. Like real-time monitoring, routine sampling can buy you critical time, and time is trauma. An earlier diagnosis affords you time to delay animal movements and deploy the SRD toolbox earlier.
Another benefit of routine sampling is that it allows for tracking disease patterns over time. For example, we know that PRRS prevalence goes up in the cooler months and down during the warmer months, which changes probability and the overall risk score of certain activities. The impact of PRRS can stay the same, but if the probability drops drastically during the summer we may choose to do things differently, like coming out of filtration when it is hotter and need to move the most amount of air.
Finally, routine diagnostic monitoring helps producers identify gaps in their biosecurity plan. If it takes 30 days to diagnose a PRRS break, the chance of knowing where the failure occurred is less likely. Working with your veterinarian on a routine monitoring plan is critical. The different phases of production (boar stud vs. sow farm vs. grow-finish) require different plans. Your veterinarian can also guide you on utilizing the different sampling methods (blood vs. processing fluids vs. oral fluids) and different tests (pathogen vs. antibody) so that you can maximize your diagnostic budget.
PRRS and SRD pose an ongoing risk to all producers, and no single action will provide complete protection. However, with long-term strategic investments, following strict biosecurity protocols, closely observing your herd, and routine diagnostics, the loss can be mitigated and addressed.
Sources
1 Gebhardt, J., Tokach, M., et al. 2020. “Postweaning mortality in commercial swine production. I: review of non-infectious contributing factors.” Translational Animal Science, Volume 4, Issue 2. https://doi.org/10.1093/tas/txaa068
2 Osemeke, O., Silva, G., et al. 2025. “Economic impact of productivity losses attributable to porcine reproductive and respiratory syndrome virus in United States pork production, 2016-2020.” Prev. Vet. Med. https://pubmed.ncbi.nlm.nih.gov/40712375/
3 Risser, J., Ackerman, M., Evelsizer, R. et al. 2021. “Porcine reproductive and respiratory syndrome virus genetic variability a management and diagnostic dilemma.” In: “Virology Journal.” BioMed Central. https://doi.org/10.1186/s12985-021-01675-0
4 Otake, S., Dee, S., et al. 2010. “Long-distance airborne transport of infectious PRRSV and Mycoplasma hyopneumoniae from a swine population infected with multiple viral variants.” In: “Veterinary Microbiology.” Elsevier. https://www.sciencedirect.com/science/article/abs/pii/S0378113510001598
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