Individual feed ingredients are not created equal, and they don’t each react identically when exposed to the porcine epidemic diarrhea virus.
Recently completed research by Pipestone Applied Research, Pipestone Veterinary Services and South Dakota State University’s Animal Disease Research and Diagnostic Laboratory isolated 18 individual ingredients commonly found in commercial swine diets, and each of those ingredients was tested for the survivability and viability of PEDV.
Scott Dee, a veterinarian with PAR, and Casey Neill, a nutritionist with Pipestone Grow-Finish in Pipestone, Minn., say the results were interesting in that “there was a subset of ingredients that harbors the virus, while there was another subset of ingredients that did not.” One ingredient of surprise that did not harbor live virus was plasma protein, which Dee acknowledged was previously considered by many as a risk factor for PEDV transmission. “At least in this particular study, that was not the case, as virus was not even viable at Day One.”
To begin the process, Dee and Neill developed a list of ingredients. Each ingredient sample was treated equally, each separated into 30-gram samples and each sample inoculated with 2 mL of PEDV. A matched set of PEDV-spiked ingredient samples was also treated with the liquid antimicrobial Sal CURB. Each of the samples was stored outdoors under wintertime ambient conditions for 30 days. “Casey and I thought this was better than storing the samples in a refrigerator where the temperature is consistent,” Dee says. “We thought that this would be more realistic, just as if it were on a farm in the winter.”
Samples were then tested on 1, 7, 14 and 30 days post-inoculation. Sample integrity was maintained by not sampling from the same container for each DPI testing. Dee says a novel approach to this study was that three forms of testing were used to determine quantity and viability of PEDV. First, a polymerase chain reaction test was used to screen the ingredients to look for viral RNA. “If positive, we tried to grow the virus in cell culture,” he explains. “If it was positive, we knew we had evidence of live virus. If negative, we used the swine bioassay as the third and final measure of viability. Using these three tests in parallel, we felt confident that if we said it was alive, it was alive, and if we said it’s not, it’s not.”
Viable PEDV was detected by VI or swine bioassay at 1, 7, 14 and 30 DPI from soybean meal, distillers dried grain with solubles, meat and bone meal, red blood cells, lysine HCL, D/L methionine, choice white grease, choline chloride, complete feed and stock virus control. PEDV was detected at 7 DPI in limestone and at 14 DPI in threonine. Supplementary testing of complete feed and soybean meal indicated viable virus out to 45 and 180 DPI, respectively.
Though the research shows PEDV is viable in some feed ingredients, while not in others, Dee admits it is truly speculation as to the reason. “We’ve asked some nutritionists that question, why it lives in some ingredients, but not others. ... maybe it’s the pH, moisture level. There’s nothing real conclusive at this time.”
As Dee says above, some ingredients presented surprises by harboring PEDV, while other ingredients previously thought to harbor PEDV were found to be clean. Dee says a finding that wasn’t a surprise was the effectiveness of Sal CURB in neutralizing PEDV in the individual ingredients.
Sal CURB is made by Kemin Industries in Des Moines, Iowa, and according to the company’s website, the product is a liquid antimicrobial, “a blend of aqueous formaldehyde 37% solution and propionic acid, [Sal CURB] is a key part of a comprehensive pathogen control program to maintain feed biosecurity. Sal CURB is an antimicrobial agent used to maintain complete animal feeds or feed ingredients salmonella-negative for up to 21 days.” Dee stresses that Kemin makes no claims toward Sal CURB’s effectiveness toward PEDV.
Furthermore, he says the product is approved for salmonella protection in pigs and poultry, “and we thought if it works on a bacterium, maybe it will work on a virus,” and the research proved that to be true.
Sal CURB’s effectiveness in neutralizing PEDV in individual feed ingredients provides another management tool for producers in tightening the biosecurity of their farm’s feed supply. “It was interesting to see the effect of Sal CURB on the ingredient list,” Dee says, “because if you can treat an individual ingredient, maybe you won’t need to treat the entire diet, but instead you can focus your intervention.”
Though this research proved Sal CURB’s neutralizing effect on PEDV, producers need to be cautioned. “This is not something that producers can just simply add to the feed,” he adds. Kemin has a stringent protocol and standards that feed mills have to meet to be able to use Sal CURB in their operations.
This work, conducted over the first two quarters of 2015, is a follow-up to previous research by Pipestone Applied Research and SDSU that found that complete feed could be one transmission mode for PEDV. Dee recommends producers continue to work with their veterinarians and nutritionists to determine where their risks exist in the feed supply.
Focus on what you know
The results of this research should raise awareness for producers. “You need to understand what the risk factors are,” Dee says. “Focus on what we know, and strive to understand more. Treat that high-risk ingredient, substitute, eliminate or change sources. … In other words, what can be done at the individual ingredient level?”
The full research paper on this recent study, completed in May, was recently published in Porcine Health Management, an open-access journal managed by BioMed Central. Dee presented these research findings at the 7th International Symposium on Emerging and Re-emerging Pig Diseases in June in Kyoto, Japan. He will also be presenting them at the upcoming Allen D. Leman Swine Conference, Sept. 19-22 at the St. Paul RiverCentre in St. Paul, Minn. Dee credits Eric Nelson and his team at SDSU for their virological expertise.
Kemin Industries provided funding during this study.