Covid – lessons learned for swine health

Lessons learned from the Covid pandemic include reducing the risk of viral infection. Feed additives can mitigate the threat via contaminated feed.

GEOFF HANDLEY* reports two studies that show the in-feed application of benzoic acid and essential oils can reduce the viral load and survivability of African swine fever virus in feed. Feed mitigation could therefore be a preventive measure for reducing the risk of contaminated feed by ASF and other viruses, while resulting in improved pig health and performance.

What can we learn from the Covid pandemic?

The worldwide Covid pandemic has thrown up many challenges to the human race, and by extension to the swine industry via personnel shortages and logistics chaos. The race for a Covid vaccine was fast and successful, unlike our industries quest for the holy grail of a vaccine against African swine fever virus (ASFv). Covid has proved that vaccines alone are not the only necessary tool in the toolbox. With Covid we have had to wear masks, and socially distance, all in the name of reducing the risk of infection. Where possible, we’ve been asked to improve our nutrition, and especially our Vitamin D levels. 

Supporting vaccine efficacy

We in the swine industry can also support the efficacy of all our routine vaccines, by reducing the health challenges and lowering the risk of infective agents entering our farms. We can also supplement pigs with vitamins and nutrients that are well known to improve immune status. It has been well described that the extra human measures we are taking for Covid, are also reducing other infectious diseases like Influenzas. The active measures we take to support our swine vaccines will also bring other benefits. Increasing the natural immunity of pigs also fends off other diseases, in addition to the targeted vaccinated disease. The feed additives that we might use to reduce viral incursion to a farm, not only enhance the vaccine effect, but then contribute to better growth rates, less mortality and morbidity, and improved feed conversion. 

Yes, Covid has taught us many lessons, but we can use at least two for our swine industry.

Actively using supplements to reduce the viral challenge, reduces the risk of the vaccine immunity response being overwhelmed.

Feed additives, can not only directly reduce viral load in feeds, but can then give extra benefits of increased growth rates and reduced feed conversion. 

Feed mitigation

Trial 1 – USA

Recent work by Dr Scott Dee (Pipestone Applied Research) proved that viruses can survive, in feed ingredients that are shipped internationally. This well publized work led to a whole new investigation on feed mitigation against the serious swine diseases of porcine respiratory and reproductive syndrome (PRRS), porcine epidemic diarrhea virus (PEDv) and Seneca A virus (SEV, as a proxy for Foot and Mouth disease). The now-famous ice-block infection methodology, was used to prove the control samples had been infected, as were the pigs that were fed the infected feed. Introducing a feed mitigant additive, to kill the in-feed viruses proved successful in some cases, with the blend of Benzoic Acid and Essential Oils being a top performer of the 15 products on Dr Dees’ trial (Table 1, only data for VevoWin is shown).

The blend of benzoic acid and essential oils cleared the 3 tested viruses from the feed, and indeed allowed significantly improved growth rates for the feeds that were treated with the blend (Table 1). In the face of viral infected feeds, reducing this challenge route for PRRS and PEDv, will ensure that the PRRS and PEDv farm vaccine protocols will be free to work on other routes of infection.

Table 1: Summary of percent positive pigs and pens by virus type across treatment and control groups collected at day 15 

Trial 2 – China

A recent study by Dr Heng-Xaio Zhai and team, has also shown that the same benzoic acid + essential oil blend at 5kg/t, cleared ASFv-infected feeds. Dr Zhai’s work also showed that this clearance occurs within a single day, being a significantly lower holding time than currently used for some ingredients at feedmills or their commodity supplier (Table 2).

Table 2: Effect of pure benzoic acid and the combination of pure benzoic acid and nature identical flavorings on hemadsorption and detection of ASF virus by real time-PCR at different days post-inoculation (dpi) in phosphate-buffered saline.


There is an exciting, but hugely difficult race to create a robust and successful vaccine against ASFv. Recent results in the Philippines and Vietnam hold some promise, but are not yet available for industry use. Reducing the challenge of ASFv via the oral feed route, can be achieved via feed mitigation, so can be a useful tool while we wait for success in the various ASFv vaccine projects.

When reviewing your vaccine strategies on farm, consider adding feed mitigation against oral route, viral infection. Reducing the incoming challenges, will give your vaccine program the best chance to achieve its maximum efficacy.

*Geoff Handley ([email protected]) is Swine Marketing Manager for Greater APAC with DSM Nutritional Products Asia Pacific. References are available on request to the author.

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Based and working in the region.