By Fernando Sampedro, Pedro E. Urriola, Jennifer van de Ligt, Declan C. Schroeder and Gerald C. Shurson, University of Minnesota

While a plethora of research describes the survival of pathogens after artificial inoculation of feed ingredients, there is a void in formal evaluation of the survival of the virus after multiple steps in the processing chain. In addition, there is absence of microbiological regulatory thresholds for viruses in animal feed.

Towards this goal, a performance objective in food safety represents the maximum concentration or frequency of a microbiological hazard (viruses in this case) at a specific point of the feed ingredient processing chain (before consumption). The calculation of PO contributes to a potential food safety objective, which is the maximum concentration or frequency of the hazard in food at the time of consumption. Calculation of FSO requires information currently not available or requiring multiple untested assumptions. Therefore, the establishment of performance objectives represents a proactive approach towards ensuring the absence of infectious viral particles in feed ingredients for pigs.

A study conducted by Sampedro et al. aimed to propose a performance objective, targeting reductions of -7.0 to -7.3 log TCID50/g (Tissue Culture Infectious Dose at which approx. 50% of wells show signs of infection). Batch sizes of 10, 15 and 20 tons of SDPP were selected to represent typical industry scenarios of plasma processing. Data on days to virus inactivation by one TCID50 log (d-value) were used for their relevance to the pork industry.

Initial assessment involved estimating the initial viral load of non-reportable (porcine epidemic diarrhea virus) and reportable swine pathogens (African swine fever virus). Porcine plasma is used as model process for its multiple steps and industry actions of feed safety. A survey on viremia suggests a PEDV concentration in raw plasma of -1.0±0.6 log TCID50/mL, this was calculated via a TCID50-qPCR derived standard curve, while the mean ASFV concentration was estimated at 0.6 log HAD50/mL (0.1-1.4, 95% CI) using similar procedure. These concentrations were calculated assuming that there would be viremia during a pre-clinical portion of the disease outbreak and that both diseases are managed differently.

The investigation subsequently explored various processing modalities to attain the proposed POs. Two primary scenarios were evaluated: the baseline, comprising spray-drying coupled with extended storage, and the baseline augmented by ultraviolet radiation treatment. Efficacy assessments were conducted regarding the attainment of PO compliance for both PEDV and ASFV across the processing scenarios. The baseline and baseline + UV processing strategies exhibited robust performance, with >95% effectiveness observed in PEDV elimination across different batch sizes. Similarly, for ASFV in SDPP during pre-clinical conditions, all processing scenarios achieved 100% compliance with the POs, ensuring complete eradication of infectious viral particles.

While the present findings represent significant strides in mitigating viral contamination in porcine feed ingredients, further elucidation of the mechanistic underpinnings driving virus inactivation during feed storage is warranted. Such insights are pivotal for informing and refining feed safety risk management strategies on a global scale, thereby fortifying the resilience of swine production systems against viral incursions.

In summary, this study shows a concerted effort towards elevating feed safety standards and safeguarding swine health. Through the integration of scientific rigor of microbiological risk assessments and pragmatic interventions of performance objective. This study underscores a paradigm shift towards ensuring the virological integrity of porcine feed additives moving away from hazard characterization towards risk based models.

UMN. Table 1. African swine fever virus concentration (mean log TCID50/g) after spray drying (SD), heated storage (HS), or ultraviolet light processing and percent of batches compliant with the performance objectives at three batch sizes of Spray Dried Porcine Plasma. 1. Calculations for African swine fever virus before onset of clinical signs and regulatory intervention. 2 Assuming solids concentration from 8 to 30% (3.5 concentration factor). **When sd was not estimated in the original study, a default value of 0.8 was used based on the natural microbial variability by International Commission Microbiological Safety in Food (2018).