# Assessment of the Relationship Between Bioexclusion Practices Applied in Wean-to-Harvest Sites and PRRS Outbreaks

## TL;DR

This study identifies biosecurity practices that increase or reduce the risk of PRRS outbreaks in swine farms, helping farmers improve animal health and reduce disease spread.

## Contribution

The study provides new insights into specific biosecurity practices that significantly influence PRRS outbreak odds in wean-to-harvest sites.

## Key findings

- Transporting pigs of unknown PRRS status, using rendering, and employee cohabitation increased PRRS outbreak odds.
- Exclusive equipment use and overnight breaks for multi-site workers reduced outbreak odds.
- Finisher sites and higher swine site density within one mile increased the risk of PRRS outbreaks.

## Abstract

Porcine reproductive and respiratory syndrome (PRRS) is a major disease affecting pigs in the United States (U.S.), causing economic losses and threatening animal health. It can spread between sites through infected animals or contaminated people, vehicles, and equipment. This study followed groups of pigs at 95 swine sites in the Midwest from nurseries, finishers, and wean-to-finish facilities to determine farm practices associated with PRRS outbreaks. Oral fluids were collected every four weeks to detect infection, and sites were surveyed once about biosecurity practices. The results indicate that transporting pigs of unknown PRRS status, using rendering, and employees living with people who worked on other sites were associated with increased incidence of PRRS outbreaks. In contrast, having a designated parking area, using equipment only for one farm, and requiring overnight breaks for workers who visit multiple sites reduced the odds of outbreak in the univariate analysis. In the multivariable model, sites located within one mile of another swine site also faced higher odds. These results can help pig farmers and the swine industry focus on practices that lower the odds of disease and improve animal health.

Porcine reproductive and respiratory syndrome virus (PRRSV) is a significant cause of economic loss in the swine industry, yet its control remains challenging in wean-to-harvest sites. This prospective observational study followed 95 wean-to-harvest sites across six U.S. states for one production cycle. Sites were required to be PRRSV-negative or vaccinated with a modified live virus (MLV) and free of major coronaviruses. Outbreaks were defined as RT-qPCR-positive in unvaccinated sites or detection of ORF5 sequences distinct from the MLV strain. Biosecurity data were collected through a survey, and oral fluids were tested every four weeks. PRRS outbreaks occurred in 14/42 nurseries (33.3%), 8/12 wean-to-finish (66.7%), and 35/41 finishers (82.4%), with lineage 1C.5 most frequently detected. In univariate models, higher odds of outbreaks were associated with transporting pigs of unknown status (OR 9.80, 1.73–55.37), rendering (OR 6.47, 1.62–25.84), and employee cohabitation (OR 6.15, 1.51–25.09). Protective factors included exclusive pumping equipment (OR 0.07, 0.01–0.43) and overnight downtime for multi-site workers (OR 0.15, 0.04–0.56). In multivariable models, finisher sites (OR 17.47, 2.44–125.19) and greater swine site density within one mile (OR 1.62, 1.09–2.41) significantly increased outbreak odds. These results support targeted biosecurity practices, helping farmers and the swine industry reduce PRRS outbreaks.