Traditionally, the U.S. swine industry's biosecurity efforts have been focused on the breeding herds, with limited actions taken in grow-finish. However, recent research has shown that 55% of growing pigs that were negative for porcine reproductive and respiratory syndrome at placement are positive at marketing. As veterinarian Chelsea Ruston points out, there are economic costs associated with that as well — a loss of $2.29 per pig placed due to higher mortality and survivability rates (Holtkamp et al, 2012).

"Data from the Swine Disease Reporting System demonstrated that an increase detection of PRRS in breeding herds is typically preceded by an increased detection in grow-finish pigs, suggesting that this grow-finish population is a major source of virus for outbreaks in breeding herds, especially in those high-dense pig areas (Trevisan et al, 2019)," Ruston says. "Furthermore, PRRS isn't the only thing that we should be concerned about. PED [porcine epidemic diarrhea] as well can cause reduced average daily gain, and it was reported in one system to reduce the average daily gain by 21.4%, with the introduction of PED late in finishing (Pavlovic, 2018)."

The Iowa State University Swine Medicine Education Center instructor and associate veterinarian says one event that can pose a significant risk for introducing a virus into a grow-finish herd is marketing. With finishing pigs in the U.S. typically marketed over several weeks, Ruston says after the first or second cut is taken from a barn, it leaves the other pigs in the barn vulnerable to infection and to become a source for a virus to spread.

"We know trailers serve as a source of transmission for PRRS and PED, and this has been well documented. And then harvesting plants, slaughter plants receive animals from many sources daily. And it's also been shown that livestock trailers used to haul pigs to market are contaminated with virus," Ruston says. "Marketing is a pretty high probability that that livestock trailer is becoming infected once it drops pigs off at the harvesting plant."

The next potential biosecurity breach for grow-finish operations is when the livestock trailer is washed, Ruston says, as there is so much industry variation on how the livestock trailers are being handled after load-outs for marketing.

"Some will do the wash, disinfect and bake, and some don't have the infrastructure to get every truck washed before picking up another load of market hogs," Ruston says. "Even if they are being washed, they're not being washed 100% correct, 100% of the time, so marketing has a really high probability of spreading disease. However, there's been really little research on if and how frequently contamination from the livestock trailer is transferred to the barn."

Glo germ highlights path
Ruston and Derald Holtkamp, a professor and veterinarian at Iowa State University's College of Veterinary Medicine, decided to conduct a pilot study to see whether Glo Germ, a fluorescent powder that shows up under ultraviolet light, could be used to better understand the transfer of contamination from livestock trailers to the center alleyway in grow-finish barns during a marketing event. The team mixed 216 grams of Glo Germ with dry wood chips, and a half-liter of obstetrics gel (to keep the Glo Germ from dissipating from wind or movement) and spread it evenly on the floor of a livestock trailer right inside the roll-up door that opens to the chute.

After the pigs were loaded onto the trailer, Glo Germ was detected inside the load-out chute, load-out alleyway, center alleyway of the barn and first three pens adjacent to the load-out alleyway on both sides of the center alleyway. Because pigs often lunge off the trailer and lose traction, the researchers found some wood chips were kicked up from the livestock trailer back onto the load-out chute. They also could spot, from the Glo Germ, violations of lines of separation between the livestock trailer and the chute.

"People do not always honor the line of separation between the livestock trailer and chute. Sometimes their boots will slip over, or their board, or in the case of animal welfare, when a pig goes down while loading," Ruston says. "Pigs obviously don't always honor that line of separation. They'll turn around from the livestock trailer and run back onto the chute sometimes back into the barn, so it's really easy to see how a person that's on that load-out can pick up something on boots or boards and bring it back into the barn."

Staged loading
Since it is known that viral contamination can be transferred from contaminated livestock trailers to the pigs in the barn during loading, Ruston and team decided to take their Glo Germ testing further and see if staged loading could reduce the frequency of contaminated particles moving from livestock trailers to the barn during a load-out. Similar to standard loading — where there is a first line of separation between the livestock trailer and the load-out chute — staged loading also has a second line of separation between the load-out alleyway and the remainder of the barn.

When loading, the driver of the livestock trailer stays on the trailer. One member of the load-out crew is stationed to the load-out chute, load-out alleyway and buffer zone. The remainder of the load-out crew is in the center alleyway and pens. Lines of separation are placed between each zone, and no members are allowed to step into other zones during load-out.

Twenty commercial wean-to-finish barns across Iowa were part of the study, with 10 replicates per treatment group (staged vs. standard). On the last load-out of the night, 216 grams of Glo Germ, OB gel and wood chips were mixed and spread evenly on the floor of the livestock trailer just inside the roll-up door. The loading procedure that was then assigned that night was observed.

To measure contamination, the team used a grid with a total of 264 squares, and counted and recorded the 5-by-5-centimeter spreads within that grid with any Glo Germ present. The level of contamination was evaluated at several different points within the load-out chute, load-out alleyway before the second line of separation and the center alleyway after the second line of separation.

Added layer of biosecurity
Compared to the standard loading procedure, the researchers found fewer squares with Glo Germ in the staged loading at all of the measurement points, specifically in the center alley of the barn after the second line of separation. However, Ruston says with either treatment group, the first line of separation was not always honored, nor was the second, especially with pigs turning around and going back over the line. Ruston also points out that not all barns were set up for staged loading.

"Many times during the study, we found it difficult to try to set up buffer areas, which we referred to for that person's station and the load-out chute, to get out of the way of the pigs, so you may need to do some thinking about that if you're trying to implement something like this," she says.

While the staged procedure was effective at reducing Glo Germ transfer from the livestock trailer to the barn, Ruston says it didn't completely eliminate it, and that's something to keep in mind with pathogen transfer.

"Bringing a dirty livestock trailer back to the barn is a really risky event, and there are opportunities to improve on the staged loading procedure," Ruston says. "This is going to be highly dependent on the barn as to whether they can implement this. And the effective use of gates or barriers could maybe be another option at the second line of separation to try to keep pigs from turning around at that point."

Finally, she says training load-out crews is essential for staged loading to work.

"Be sure to explain to them why you're doing it, putting in some auditing and monitoring it as well," Ruston says.

References
Holtkamp D.J., Kliebenstein J.B., Neumann E.J., Zimmerman J.J., Rotto H., Yoder T.K., Wang C., Yeske P., Mowrer C., Haley C., 2013, "Assessment of the economic impact of porcine reproductive and respiratory syndrome virus on United States pork producers," J Swine Health and Production 21(2):72-84

Pavlovic, L., 2018, "Experiences managing wean-to-finish PEDV in a production system," proceedings from 49th annual meeting of American Association of Swine Veterinarians, San Diego

Trevisan, G., Linhares, D., 2019, "Swine Disease Reporting System (Reports 18 and 19)," swinehealth.org/domestic-disease-surveillance-reports