The sow farm manager was doing everything right from a biosecurity standpoint. The barn was filtered. The farm team adhered to strict mechanical biosecurity protocols for trucks, people, supplies – basically everything you could imagine. The farm had a clean source for animals and semen.

When the sows stopped eating one day, the manager closed the feed line because he suspected mycotoxins in the feed. He preserved the feed that was left in the bin and immediately called up Scott Dee, DVM, and emeritus director of discovery and innovation at Pipestone Applied Research. Dee was less than an hour away from the farm at the time and jumped in his truck.

“It reminded me of the first porcine epidemic diarrhea (PED) case back in January 2014 when we took paint rollers and collected all the interior leftover material in the bin,” Dee says. 

He stopped at a hardware store on his way, buying a long pole and paint rollers to see what he could find. But this time he had a different target in mind – he was going to look for porcine reproductive and respiratory syndrome (PRRS) virus. 

“It's really fortuitous that the manager called me, shut off the line and preserved the sample so I could sample the bin of feed that these index cases were consuming,” Dee points out.

For the first time in history, Dee was about to discover PRRS virus can live in feed.

A Nagging Suspicion

“In our research on the susceptibility of viruses to survive in feed, we've kind of neglected PRRS virus,” Dee says. “Many years ago, PRRS was shown not to survive in feed at all. However, at the time of this study, they used a very insensitive laboratory test called virus isolation. PCRs and bioassays didn't exist. Still, everyone kind of wrote it off.”

Still, Dee says there’s always been this little subset of farms within Pipestone – highly biosecure sow farms in areas of low-density swine production – that would break with PRRS for unknown reasons. 

“I can’t say PRRS transmission through feed is a major risk. But I think it's a big enough risk that we should talk about it. We've always wondered if it was possible that feed could bring it in,” he says.

The problem with figuring out the transmission of virus in feed in a farm setting is that the feed gets eaten and new feed comes in, Dee explains. 

“You don't have anything to sample that was representative of what you just went through. This manager was astute enough to shut off the line and call me,” he says.

PRRS Can Be Transmitted Through Feed

When Dee got to the farm, he collected four samples from the index bin, which were positive for PRRS virus RNA by RT-PCR with cycle threshold val¬ues ranging from 26 to 29. All control bin samples were PCR negative.

“As the paper says, we found viral RNA and pretty strong CT levels in those feed samples that we collected with the paint rollers,” Dee says. “We fed that back to pigs in an experiment and they became infected with PRRS. The sequence of the virus was the same as the one discovered in the sow herd.”

The farm component and the lab component of this research study required a lot of luck and the stars to align, he adds. 

“It's the first proof that PRRS virus can be alive in feed and can be transmitted through consumption of feed. That’s never been discovered before,” Dee emphasizes.

How Big is the Risk?

Dee says the conservative scientist in him says he can’t really answer that question, but it’s probably low. However, the opportunity to secure a sample like this is pretty rare. 

“It might be a bigger concern than we make it out to be. If we all had that same sampling opportunity, we might find it a lot more than we think. The truth is we don't know how big of a risk it is. That's a good question,” Dee says.

Layer Biosecurity

Layering biosecurity protocols is key, Dee says. Feed is a component of the concept they’ve coined as “next-generation biosecurity,” that works in unison with mechanical biosecurity, aerosol biosecurity and a negative source of breeding stock and semen. This sow farm did not have a mitigant in the sow diet. 

“To really do next-generation biosecurity, you need that complete package. You can't do one without the other. If you clean your trucks well, and you don't filter your barn, you could get infected. If you filter your barn, but don't clean your trucks well, you could get infected,” he says. “And this case shows that you can do everything right and still get infected if you don't have the feed in place.”

This study, published in the Journal of the American Veterinary Medical Association, strengthens the need for a comprehensive layering of protocols, Dee says. But he acknowledges that cost can be a detriment when it comes to incorporating feed mitigants. 

“I don't blame farmers – it's kind of like buying insurance. Sometimes you just can't buy insurance for everything, so you insure what you can. However, we've never had information like this before, to say the worst swine disease in the world that we've been dealing with for 36 years, may be transmitted through this route,” Dee says. 

The new, highly virulent isolates of PRRS is one more reason to consider incorporating feed mitigants, especially in sow diets. 

“Hindsight is 20/20. If this farm had used a feed mitigant, this wouldn't have happened because PRRS is very easy to neutralize. Basically, every feed mitigant we've tested can inactivate PRRS because it’s not that stable of a virus,” he adds. “If we ever get African swine fever, it's been well shown that some mitigants can neutralize ASF as well as PED and other viruses.”

Dee says there is no question anymore that PRRS virus can be transmitted through feed. Although the frequency of how often it happens isn’t known, this research answers the question of if it can happen in a field setting that is backed by a laboratory experiment. 

“Producers should definitely consider this as a risk and talk to their vet and nutritionist about it,” Dee says. “And, if they're not already doing so, producers should consider using a feed mitigant in their sow diets.” 

Read the journal article here.

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