Editor's note: the following is from a presentation by Ana Paula Poeta Silva and colleagues at Iowa State University, the University of Minas Gerais, Brazil and the University of Goias, Brazil, during the 2024 James D. McKean Swine Conference.

Manure pumping is a common practice for repurposing waste from pig sites as a valuable fertilizer for crop fields. However, manure agitation and spreading can inadvertently move pathogens from one location to another, serving as a dangerous fomite and potentially jeopardizing the health of on-site pigs.

This study aimed to describe the association between manure pumping practices and health outcomes in wean-to-market populations. One retrospective and one prospective study were conducted separately.

Retrospective study

This study was used to estimate the odds of a porcine reproductive and respiratory syndrome virus (PRRSV) or porcine epidemic diarrhea virus (PEDV) outbreak within four weeks following a manure pumping event from the site, or the site being located within 1-, 3-, and 5-miles from a field receiving manure from a different location. The population of interest was wean-to-market lots from one system that pumped manure between July 2020 and December 2022. The unit of analysis was a week-lot event; the cases were lots that reported a PRRSV or PEDV outbreak.

Controls did not report a PRRSV outbreak and were selected to match cases spatially (within a radius of 6.2 miles from case lots) and temporally (placement dates within a 4-week interval from outbreak dates).

A total of 2,903 lots were placed across 612 wean-to-market sites; of those, 1,444 lots had at least one pumping event with a reported 517 PRRSV outbreaks and 114 PEDV outbreaks. Following the eligibility criteria to select controls, the analysis included a total of 1,301 lots with 517 of those reporting PRRSV outbreaks (cases) and 752 lots reporting at least one pumping event (exposed lots). Pumping and manure spreading were associated with an increased frequency of PRRSV outbreaks.

The odds of having a PRRSV outbreak within 4 weeks after pumping was 1.71 times higher than in lots that were not pumped. The odds of having a PRRSV outbreak within 3 weeks after receiving manure at a 1-mile distance was 4.45 times higher than those not receiving manure. No associations between PEDV outbreak and manure pumping or spreading were detected in this dataset.

Prospective study

A longitudinal study investigated the incidence of PRRSV and PEDV in wean-to-finish pigs after manure pumping events in 2023. Eighty-four barns that pumped manure during this timeframe were selected for PRRSV and PEDV RNA testing in oral fluid and manure pit samples before (between one to seven days) and two weeks after manure pumping. Six oral fluids were collected per barn. Four manure samples were collected from the manure pits (one sample per pit from each barn).

Samples were pooled (1:4) by barn on the day of collection. Barns were included in the analysis if they tested PRRSV and PEDV negative in oral fluid samples before pumping.

Of the 77 barns sampled, 25 and 74 tested negative respectively, for PRRSV and PEDV prior to pumping. For the barns testing negative for PRRSV prior to pumping, 88% of oral fluid samples and 52% of manure samples tested PRRSV-positive following manure pumping. As a result, the odds of a barn testing positive for PRRSV after pumping were 2.34 times higher. Only two of 74 collected oral fluid samples tested PEDV-positive post-pumping (2.7%).

Conclusions

Both the retrospective and prospective studies showed that manure pumping practices were associated with PRRSV outcomes: outbreak and detection. The odds of a PRRSV outbreak within a 4-week window were greater when the site was pumped and was near a field receiving manure. The odds of a previously PRRSV-negative barn becoming PRRSV-positive increased significantly after manure pumping. Veterinarians and producers need biosecurity and biocontainment strategies associated with pumping manure out of sites or when a site is near a field receiving manure.