Validation of sampling methods in bulk feed ingredients for detection of swine viruses

Animal feed can be contaminated with fomites carrying swine viruses and subsequently be a vehicle for viral transmission. This contamination may not be evenly distributed, and there is no validated sampling method for detection of viruses in animal feed or ingredients. The purpose of this experiment was to evaluate the sensitivity of ingredient sampling methods for detection of porcine epidemic diarrhoea virus (PEDV). No animals were used in this experiment, so approval from an animal ethics committee was not necessary. Thirteen kg soybean meal was used in a 2 × 2 factorial plus a control, with 2 doses of PEDV (Low: 10³ TCID₅₀ /g versus High: 10⁵ TCID⁵⁰ /g) and two sample types (individual probes versus composite sample). Soybean meal was confirmed PEDV negative, then loaded into individual, 1-kg polyethylene tote bags with PEDV introduced after loading the first 100 g. There were six replicates per PEDV dose plus a control. Ten individual probes or one composite sample per bag were created and analysed for PEDV via qRT-PCR. The interaction, dose and sample type were significant for both PEDV presence and quantity. No control samples had detectable PEDV. At the low dose, no PEDV RNA was detected in individual probes or composite samples, but was confirmed in 100% (32.4 C_t ) of the inoculant samples. This is likely due to loss of sensitivity during the analysis process, which has been previously reported to cause a loss up to 10 C_t when detecting PEDV in feed or ingredients. At the high dose, only 37% (37.7 C_t ) of the probes had detectable PEDV RNA. Composite samples were more sensitive (p < .05), with PEDV RNA detected in 100% of samples (35.7 C_t ). In summary, sampling bulk ingredients for PEDV should include compositing at least 10 individual samples. Future research is needed to identify alternative methods that have a similar sensitivity, but require less time and effort to collect such a sample.