5 September 2025

3 minute read

By: Chris Wright

North America

[Edited presentation by Scott Dee, R. Edler, Pipestone Research; L. Brands, A. Schelkopf, J. Nerem, G. Spronk, Pipestone Veterinary Services; M. Kikuti, C. Corzo, University of Minnesota, USA, during the 2024 North American PRRS Symposium]

Porcine reproductive and respiratory syndrome virus (PRRSV) is a globally significant pathogen of pigs. Controlling the entry of PRRSV to swine breeding herds is critical to maximizing animal health, welfare, and productivity. The objective of this study was to evaluate the impact of improved biosecurity on the PRRSV incidence risk and to understand whether these practices influenced breeding herd productivity.

A retrospective cohort study evaluating PRRSV incidence risk was conducted over a 3-year period, from July 1, 2021, to June 30, 2024, across breeding herds from a commercial swine production system (Pipestone, MN). Over the course of the project, 69 herds/321,013 sows participated in year 1, 76 herds/381,404 sows in year 2, and 75 herds/384,207 sows in year 3.

Across the database, two cohorts of herds which differed in their level of biosecurity practiced were classified as Next Generation Biosecurity (NGB) COMPLETE or NGB INCOMPLETE. Next Generation Biosecurity uses science-based measures for the prevention of the PRRS virus and improves productivity in swine breeding herds. The protocols evaluate mechanical, aerosol and feed risk at the sow farm level, instead of only focusing on mechanical risk.

PRRSV incidence risk was calculated using MSHMP guidelines for each disease year, and over the 3-year period. The difference in the proportion of PRRSV positive herds (# new PRRSV infections/# breeding herds) across the 3-year period was analyzed for significance by Chi square, the cumulative PRRSV incidence risk across all herds during the 3-year period was calculated, and the association between the level of biosecurity (COMPLETE vs INCOMPLETE) and disease burden (PRRSV incidence risk) was tested by Chi square.

In addition, differences in key performance indicators (KPIs) between 43 NGB COMPLETE HERDS and 19 NGB INCOMPLETE herds over disease years 1 and 2 were analyzed for significance by T test. For assessment of KPIs, only herds that provided two complete years of data during disease year 1-2 and were controlled by genetics, nutrition, farm management, employee training programs, animal handling protocols, record keeping, and animal health were selected. Finally, neighboring swine density within an 8.3 km radius of each breeding herd was calculated over the 3 years.

The proportion of positive herds was 6/69 (8.7%) in year 1, 7/76 (9.2%) in year 2, and 11/75 (14.6%) in year 3 (p = 0.77). The cumulative incidence risk was 8.0%, and significantly lower (p < 0.0001) PRRSV incidence risk was associated with NGB COMPLETE vs NGB INCOMPLETE herds.

Regarding differences in KPIs, NGB COMPLETE herds had higher total born piglets/farrowing (p = 0.047), and pigs weaned/female (p = 0.021), lower preweaning mortality (p = 0.013) and shorter weaning to first service interval (p = 0.007) than NGB INCOMPLETE herds. In addition, while not statistically significant (p = 0.15), NGB COMPLETE herds also had an increase of 0.91 pigs weaned/mated female/year. Finally, no differences were observed in the area density surrounding NGB COMPLETE and NGB INCOMPLETE herds across the 3 years of the study.

This retrospective cohort study provides evidence that NGB, while not perfect, provided sustainable control and prevention of PRRSV and improved breeding herd productivity. This is the first report of successful PRRS control in a large commercial production system for this extended period of time.