Inactivation Of Viral Contamination Of Complete Feed Using Extended Storage Time, By Doug MacDougald South West Ontario Veterinary Services

By
Jim Eadie
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It has become more clear over time that feed ingredients and complete feed can present a biosecurity risk. Prevention of contamination is obviously important, but it can be a daunting task because there are many critical control points. Another approach to feed biosecurity involves the deactivation of pathogens in feed through the use of heat, feed additives, or even irradiation. Techniques such as irradiation can have a negative effect on feed ingredients such as enzymes or vitamins.

Another approach is to extend storage times of feed and feed ingredients. The use of extended feed storage times can increase the potential for unintended consequences such as reduced palatability, degradation of nutrients, increases in mycotoxins, or increased microbial contamination.

These researchers wanted to validate the use of extended storage times for complete swine feed for the inactivation of several swine viruses. In this study, complete feed was inoculated with 10mL of 1×10^5 TCID50/mL of porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV), and Senecavirus A (SVA). Feed was stored for 58 days at 23.9°C in either an environmentally controlled container or in a container with ambient temperature consistent with fall climate changes in the Midwest US.

Measures of feed quality were also evaluated at the initiation and conclusion of the storage period. This included screening for mycotoxins, characterization of select microbiological measures, and evaluating the stability of phytase and dietary vitamins.

Findings:

  1. Phytase Levels:
    • Showed evidence of normal levels of decay over 58 days.
    • Were within normal tolerances that satisfied the intended feed label claim.
  2. Vitamin Levels:
    • Vitamin B5 levels were reduced over 58 days.
    • No evidence of reduction for vitamin A, D3, or E under any storage conditions.
    • Variation in test results can be high for vitamins due to sampling and analytical variation.
  3. Microbiological Profiles:
    • Controlled Anaerobic Storage (23.9°C):
      • No detectable yeast (<10 cfu/g), mold concentration (90 cfu/g), and aerobic plate count (260 cfu/g) at 58 days.
      • All parameters were lower than samples collected on day 0.
    • Ambient Storage (Midwest US Fall Weather):
      • Slight increase in yeast count (490 cfu/g), still within normal parameters found under field conditions.
    • No detectable levels of Salmonella sp., E coli O157

      , Staph aureus, or Clostridium perfringens at the beginning or end of the storage period.

    • No evidence of mycotoxins at the beginning or end of the storage period. Thirteen different mycotoxins were tested.
  4. Swine Bioassay:
    • Pigs exposed to inoculated feed stored for 58 days showed:
      • No signs of PEDV or SVA replication (detected by PCR screening of oral fluids and serum antibody screening).
      • No signs of PRRSV infection based on absence of PRRSV antibodies (an unintentional aerosol transmission of PRRSV from the positive control room was noted).

Positive Control Findings:

  • PRRS was detected in the positive control room.
  • SVA clinical signs were detected even though there was no evidence of seroconversion at 27 days post-exposure.
  • No evidence of PED in the positive control room (challenge level for PEDV was perhaps too low to cause infection).

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