Harvest plants serve as concentration points, receiving dozens to hundreds of trailers from multiple sources with varying infectious statuses, which may contribute to facility contamination, says Lucas Ferreira of the University of Minnesota. Everyone knows these sites serve as a mixing pool for diseases, but just how much of a concern is it?
“Limited information is available on trailer contamination risk and factors associated with unloading pigs at harvest plants,” he shared at the 2025 Allen D. Leman Swine Conference. “Our study aimed to quantify market hog trailer contamination during unloading and identify associated risk factors.”
Knowing what’s happening at the harvest plants is a step forward in figuring out how to strengthen biosecurity tactics and protocols, he says.
In this ongoing study, 15 environmental samples have been collected biweekly since calendar week 47 of 2024 at a Midwestern U.S. harvest plant. Samples are collected from the unloading dock and trailers (both before and after unloading pigs) and RT-PCR tested at the University of Minnesota Veterinary Diagnostic Laboratory (VDL) for porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV)/porcine delta coronavirus (PDCoV)/transmissible gastroenteritis (TGE), and Senecavirus A (SVA). Other information including trailer origin, sanitation status, destination, and driver or plant employee behavior during unloading are also being recorded.
What Has the Study Revealed So Far?
Ferreira says 88% of samples have been collected with PRRSV (50.3%), PEDV (59.1%), PDCoV (71.2%), and SVA (45.9%) being detected in the dock samples. He notes most of the SVA positive samples were detected at the end of 2024 and early 2025 and now in the summer there has been a important increase. Here are some key takeaways so far:
• Before unloading pigs, PRRSV (34.3%), PEDV (26.5%), PDCoV (40.1%) and SVA (21.2%) were detected in the trailers.
• After unloading, the percentage of contaminated trailers increased for all pathogens as PRRSV (43.4%), PEDV (47.5%), PDCoV (62.1%) and SVA (38.2%) were detected in the trailers.
• A total of 100 out of 344 trailers tested negative on arrival at the plant, and 75 out of the 100 were contaminated with at least one pathogen.
• When the dock was contaminated, the odds of the trailer becoming contaminated increased significantly for PEDV, SVA, and PDCoV but not for PRRSV.
• The odds of trailer contamination were 1.9 times higher for PEDV, 2.3 times higher for SVA, and 2.73 times higher for PDCoV. For PRRSV the odds of becoming contaminated were 1.23 times higher for PRRSV, although it was not statistically significant.
• A total of 18.6% of PDCoV-contaminated, 20.2% of PEDV-contaminated, 17.3% of PRRSV-contaminated, and 16.7% of SVA-contaminated trailers went on to load new pigs on a farm without being washed after unloading.
Strengthen Biosecurity Procedures
The results show trailer contamination is occurring at a significant rate. Ferreira points out that it is difficult to know the health status of the pigs before they arrive at the plant.
“These findings indicate that a significant proportion of trailers arrive at harvest facilities already contaminated, likely due to pathogen shedding by pigs or inadequate sanitation between loads,” Ferreira says. “PEDV and PDCoV contamination was consistently detected throughout the study.”
This study is ongoing, he notes, and three visits (45 trailers) remain.
His research highlights the need for better practices in transportation, particularly when it comes to cleaning and disinfection protocols (washing the trailer) after unloading at the plant, he emphasizes.
“Many drivers currently do not plan to wash trailers after unloading, and I believe this happens for two reasons: first, in many cases, producers may not be requesting it, and second, drivers need better training regarding biosecurity procedures, as many do not fully understand their importance,” Ferreira says. “Since contamination is a challenge that affects the entire industry, producers, drivers and plant facilities need to work together to improve biosecurity procedures during and after unloading pigs at the plant, to reduce the contamination.”
Researchers include Lucas Ferreira, Mark Schwartz, Marie Culhane and Cesar A. Corzo, all of the University of Minnesota.
