A new study provides evidence that the processes associated with manure pumping and land application pose a risk for the introduction of porcine reproductive and respiratory virus (PRRSV) into pig sites. Researchers say there was plenty of porcine epidemic diarrhea virus (PEDV) RNA detected in pit samples from most herds visited despite the absence of clinical disease or PEDV in oral fluids.
Manure removal, a common practice typically performed twice yearly at nursery and grow-finish pig sites, involves the manure then being spread on fields surrounding those sites for its nutritional and fertilizing value to grain and forage crops. Not only can diseases be introduced through manure agitation, but pathogen spread can take place during the pit pump out process or during the application of contaminated manure on nearby fields.
The research, funded by the Swine Health Information Center Wean-to-Harvest Biosecurity Research Program, in partnership with the Foundation for Food & Agriculture Research and Pork Checkoff, investigated the risks of manure pumping to introduction and spread of pathogens across wean-to-finish sites. It also characterized the level of risk for specific manure pumping practices or site characteristics, such as nursery compared to grow-finish, storage in deep pits or lagoons, timeline of pumping and spread relative to pig placement, and distance of crops for manure application.
Led by Ana Paula Poeta Silva and Daniel Moraes, working with the principal investigators Daniel Linhares and Gustavo de Sousa e Silva of Iowa State University, the study sought to define the risk of manure pumping on disease introduction to pigs. The objectives included 1) identifying the risk factors for disease onset in wean-to-finish sites following manure pumping and spread in nearby fields, 2) determining the frequency of PRRSV and PEDV detection in pit samples from wean-to-finish sites and the likelihood of increasing PCR-positivity of oral fluids after manure pumping.
How the Study Worked
A retrospective study investigated pig lot- and site-level risk factors related to manure pumping and spread for PRRSV or PEDV onset in wean-to-finish sites, SHIC shared in its monthly newsletter. Specifically, the study estimated the odds of a PRRSV or PEDV outbreak occurring within four weeks after manure pumping out from the site (exposure 1) or being near a field receiving manure at 1-, 3-, and 5-miles from the site (exposure 2).
Sites in the study conducted at least one manure pumping event or received manure spread on neighboring crop fields between July 2020 and December 2022. A satellite remote-sensing system located and characterized manure pumping activities and procedures, such as sites of manure origin and crop fields of manure spread destination.
PRRSV or PEDV outbreaks were defined based on veterinarian assessment, pathogen detection in tissues, and increased mortality rate after the pumping event or receiving manure, SHIC explained. The odds of a PRRSV or PEDV outbreak within four weeks after manure pumping out from the site was calculated across all data collected. For the analyses, controls were selected to match spatially (within 6.2 miles of cases) and temporally (placement dates within a 4-week interval from outbreak dates) cases.
A total of 2,903 pig lots were placed across 612 wean-to-finish sites. Of those, 1,444 pig lots had at least one manure pumping event with 517 reporting at least one PRRSV onset and 114 reporting at least one PEDV onset. What does this mean? The odds of PRRSV onset within a four-week period following pumping and spreading manure increased 1.7 times as compared to lots that were not pumped.
Nurseries had higher odds of reporting PRRSV onset following manure pumping compared to grow-finish. Other characteristics associated with higher PRRSV risk included greater volume of pumped manure, and manure application <16 weeks post-placement. No association between PEDV outbreaks and manure pumping was detected in this dataset, the article said.
To achieve the second objective, a total of 77 growing pig barns were investigated that had no evidence of PRRSV or PEDV before the pumping process. These barns pumped manure within 10 months of the study onset and were monitored over time to investigate the frequency of PRRSV and PEDV detection before and after manure pumping. Manure pumping took place from April 2023 through December 2023. Oral fluid samples from pigs and environmental samples from the outside the manure pit were collected. Disease onset was based on at least one positive PCR result for PRRSV or PEDV.
SHIC said the results of this prospectives study demonstrated an increased likelihood of testing PRRSV-positive in oral fluids after pumping out manure. The PEDV positivity in manure was significantly higher than that of PRRSV in manure; however, there was no increase in oral fluids PEDV positivity after pumping out manure.
Manure Pumping is Associated with Outbreaks
Both study objectives provided evidence that manure pumping is associated with risk of PRRSV outbreaks.
“Understanding the risk factors associated with manure removal from wean-to-finish pig sites will enable producers and veterinarians to develop biosecurity steps and timing considerations for the pumping processes to improve bio-exclusion and bio-containment for PRRSV,” SHIC said.
Read the study’s industry summary here.
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How Does Manure Pumping Affect Disease Spread in Pigs?
10 Tips to Keep Safe When Pumping Manure
