"Challenge accepted." That must be what Scott Dee, director of research for Pipestone Applied Research, said when he took on the task of finding feed additives that could successfully mitigate the risk of virus-contaminated feed. Over the last two years, he has put 15 different feed mitigants up to the test against porcine reproductive and respiratory syndrome 174, porcine epidemic diarrhea and Seneca Virus A. The multiple feed additives tested have included medium chain fatty acid blends, organic acid mixtures, acid/aldehydes and others.
Now he has put the mitigants up to another kind of test, an "ice-block" challenge.
Published last month in the scientific journal, Transboundary and Emerging Diseases, the study was conducted by Dee and other researchers from Pipestone Applied Research, Kansas State University and South Dakota State University who used a distinctive viral challenge model to simulate large-scale commercial swine production and evaluate whether multiple feed additives could reduce the risk of viral-contaminated feed.
The study used ice blocks containing equal concentrations of PRRSV, PEDV and SVA, along with realistic volumes of complete feed supplemented with selected additives. From November 2018 to February 2020, five independent experiments were conducted involving 2,880 weaned pigs, ranging from 5 to 8 weeks of age on arrival. The pigs were either placed in the "treatment group," which were fed complete feed supplemented with a specific product, or the "positive control group," which was fed a complete feed without supplementation.
Each experiment was 25 days in length and involved a 10-day pre-challenge period for animals to acclimate to their surroundings and respective diets, followed by a 15-day post-challenge period to measure response. During the 15-day post-challenge period, feed was contaminated in each bin on day 0 and day 6, and samples were collected on days 0, 6 and 15. On day 15 post-challenge, the experiment was terminated and final samples were collected.
Based on the data recorded, the approach consistently delivered all three viruses to the treatment and control groups via natural feeding behavior. For 14 of the additives tested, pigs on supplemented diets had significantly greater average daily gain, significantly lower clinical signs and infection levels, and numerically lower mortality rates compared to non-supplemented controls.
The researchers acknowledge the success of the ice-block approach may have been enhanced by the time of year, as these experiments were conducted during cold weather which may have enhanced viral viability in the feed. They also recognize another possible criticism of this approach in that the viral load in the ice block was excessive and not representative of the actual viral load in feed under commercial conditions. However, the team says since information on the actual level of virus contamination in commercial feed is not currently available, they based the concentration using data from field samples of feed naturally contaminated with PEDV, along with multiple publications involving experimental inoculation of feed ingredients using this same amount (Dee et al., 2018; Dee, Clement, et al., 2014; Stoian et al., 2019, 2020).
While a majority of the additives evaluated mitigated the effects of PRRSV 174, PEDV and SVA in contaminated feed, resulting in improved health and performance, there is still more work to be done, Dee says. First, the products tested in this study do not have label approval yet to claim efficacy against viruses. Second, more work needs to be done to address foreign animal diseases, specifically the ability of feed additives to mitigate the risk of African swine fever virus in feed.
Finally, Dee hopes the information from this project will help motivate the swine industry, the veterinary profession and federal agencies to work together to develop a national feed biosecurity program involving the use of validated feed additives.