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PEDV-negative status doesn't stop at sow farm

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After an aggressive monitoring plan, Seaboard Foods is 100% porcine epidemic diarrhea virus-negative in all commercial finishing sites across the system.
Seaboard Foods veterinary team investigates infection rates, improves biosecurity at finishing level.

Since 2013, Seaboard Foods has seen a decreasing incidence of porcine epidemic diarrhea virus in its 333,000-sow herd across Oklahoma, Kansas, Colorado, Texas and Iowa.

Donna Drebes, a veterinarian for the third-largest pork producer in the United States, credits improvements in biosecurity, such as bakers being installed for commercial flows, the regionalization of flows and the cleanliness of farms.

However, Drebes says sporadic PEDV breaks are still occurring at the sow farm and nursery levels, with an unclear method of introduction in most cases.

"Even with the significant decrease in sow-farm and nursery PEDV break incidence, we did not know what was occurring in the commercial finishing population," Drebes says. "We assumed it was endemic, and had evidence of infection with limited clinical signs."

The Seaboard Foods veterinary services team began monitoring to better understand regional prevalence and incidence at the commercial finisher level. Two key aspects of the Seaboard Foods system are: all finishing pigs are greater than 10 weeks of age before being transferred to the finisher, and the system has no wean-to-finish sites.

Drebes says findings of the initial monitoring were not surprising. "PEDV was present in the commercial finishing system in western Kansas and the Oklahoma-Texas Panhandle," Drebes says. "We had PEDV-negative sites right next to PEDV-positive sites. In addition, some of the PEDV-positive sites sat in very close proximity to PEDV-negative sow farms and nursery sites in the Texas and Oklahoma Panhandle."

The objectives for the monitoring were to understand PEDV prevalence, when PEDV infections occurred relative to the turn and the risk factors for PEDV infection in the commercial finishing population.

"By understanding those aspects, we wanted to be able to decrease the risk of PEDV breaks in all phases of production across the system," Drebes says. "Remember, in a system having PEDV-negative status, it does not stop at the sow farms or nursery sites."

Determining site status
The team set out to determine the PEDV status of all its finishers, to find out when known negative-PEDV sites were rebreaking relative to the turn, and to compile a list of action items to prevent breaking of known negative-PEDV sites.

To determine PEDV site status, a three-part testing scheme was initiated:

* Pre-ship. One oral fluid per barn collected one week before site starts to ship.

* Post-placement (PP). One composite Swiffer sweeper collected one week after site fills.

* Clinical signs (CS). One composite Swiffer collected anytime a scour is present at the site.

All samples were tested via triplex real-time polymerase chain reaction at the Iowa State University Veterinary Diagnostic Laboratory in Ames.

Any sample with a cycle threshold (Ct) equal to or above 30 was considered genetic material, while samples below 30 Ct were considered positive. If no scours were present at a site with a Ct above 30, the site was considered negative. According to Drebes, the cutoff of 30 was based on prior experience with PCR testing in growing pigs and discussions with diagnosticians.

After interpreting the results, the sites were classified as stable (PEDV original-, PEDV indel- and porcine deltacoronavirus-negative), Line 2a (PDCoV- or PEDV indel-positive) or Line 2b (PEDV original-positive) health statuses.

"We made the differentiation between Line 2a and Line 2b based on the clinical impact at the farm level," Drebes says. "In our experience, porcine deltacoronavirus and PEDV indel are less severe than PED original."

Site status was communicated daily to field personnel through Seaboard's biosecurity positioning list and maps.

University of Minnesota analysis
Sampling began in Week 42 of 2019, and by Week 20 of 2020, Drebes reached out to the University of Minnesota swine team to help answer some more in-depth questions surrounding the 30 weeks of data.

"The three main questions I presented to the U-M swine group were the number of sites in a geographical area that had never been PEDV-negative, the number of times PEDV was introduced into a given site, and the time frame of an induction relative to the turn in weeks," Drebes says.

For data analysis, U-M researchers defined a PEDV introduction as a farm moving from stable to either Line 2a or Line 2b. The sample types responsible for turning sites positive were analyzed, as well the time in weeks between the last negative and first positive sample.

Looking over the 30 weeks of data, the U-M team found only one site in northwestern Kansas ("Kansas Northwest") that had remained Line 2a or Line 2b. Overall, the virus was introduced 123 times into 117 sites. The Oklahoma Panhandle was a low-risk area, with eight introductions into 41 farms — a 20% chance of introduction per farm. Kansas Northwest was a high-risk area with 64 introductions into 110 farms, a 62% chance of introduction per farm.

"This is important, because Kansas Northwest is an 800,000-head finishing complex that shares multiple resources," Drebes says.

The highest percent of introductions (57.36%) came from a negative PP test followed by a positive CS. The mean time between the negative PP and positive CS was 8.8 weeks.

"This showed us we were successful at cleaning up sites prior to placement of a new group of animals," Drebes says. "However, we were tracking the agent back into these clean sites."

Drebes says the Seaboard Foods veterinary services team believed fomites and shared tools may have been to blame, so their largest action item after the analysis was to invest in multisite and site-specific equipment, such as dead-haul trailers, sort boards, etc.

100% PEDv-negative
Since then, the team has made significant strides in decreasing PEDV across the entire system.

"Currently we are 100% PEDV-negative in all commercial finishing sites across the system, so this shows it is possible to drastically decrease PEDV pressure in a system," Drebes says.

Another important takeaway from the analysis was that introductions without clinical science are possible.

"There were multiple sites that tested positive without ever showing clinical signs during this monitoring period," Drebes says. "This shows that a robust monitoring scheme is essential if you want to truly establish current finisher health status."  

The Seaboard Foods veterinary team plans to continue its aggressive monitoring plan, and that includes all aspects of the system — farms, feed mills, truck washes and processing plants.

"We will need to see what happens when the high-risk season begins," Drebes says. "Again, there are multiple unknown questions at this point, such as how many breaks at all levels of the system will we see with the lower number of PEDV-positive sites, and will the high-risk time period be the same or change, given the changes in testing?"

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