Results
Aerosol viral sampling:
The air collection occurred for 3 hours, beginning at the start of the grinding process. The grinding was completed at approximately 2.5 hours, but the aerosol collection at each distance ran for the full 3 hours. An aerosol sample was collected from each device after every 60min run time (18 total samples) for PCR testing. All filter elution samples tested negative for PRRSV and PEDV by PCR. Upon receiving negative virus results on all samples, filter pads from each collection point were vortexed with saline, and PCR retesting on the resulting fluid was attempted to increase testing sensitivity. All samples were PCR negative for PRRSV on the retest; however, a single PEDV PCR positive sample was detected in one collector at the 137m (150 yards) distance with 36.55ct (cut-off used by the lab is 38ct).
Water viral testing:
A water sample collection was attempted on every well weekly. Eleven total water well samples were able to be attained through the study, as seen in Table 1. The only positive PCR result was in week five on the 0.15m well under the cornstalks biomass. Successful attempts to collect water samples were from depths of 0.15m and 0.46m, with no samples collected from the 0.91m depth.
Compost temperature by treatment and biomass type:
Regardless of compost sections microbial digestion treatment, the piles achieved similar temperature peaks, as reported in Table 2. By day three post windrow formation (pwf), each compost type reached an internal temperature of 60°C or higher and maintained that heat for at least 48 hours except for the treated section of the mixed biomass windrow that dropped to 55.6°C on day five pwf. Woodchips appeared to reach the highest peak compost temperature at 75.6°C on day three pwf. Woodchips and the treated section of the cornstalks reached temperatures >60°C by day two pwf, a day before the mixed biomass. The average high air temperature for the first five days pwf when peak windrow temperatures were met was 3°C and the low was -5.1°C. The only added moisture to the compost piles from the weather during the first five days pwf was minimal with 0.05cm of rainfall and 0.51cm of snowfall.
Compost viral testing:
Day 0 (when the carcass grinding and windrow formation occurred) revealed PCR positive results for both PEDV and PRRSV in all three biomass materials. As reported in Table 3, woodchips had a greater number of samples with PCR positive results for both PRRSV and PEDV compared to cornstalks and the combination material. Cornstalks compost provided the least amount of PRRSV and PEDV positive results. Table 3 shows that the last PRRSV positive result was detected on day four pwf in the woodchips, and PEDV was detected out to week 2 in both the woodchips and combination piles.
Swine DNA testing:
Swine DNA could be detected in the compost sample of each biomass type up to five days pwf. As seen in Table 4, at weeks 2 and 3 pwf, swine DNA could still be detected in each biomass type. Table 5 shows the results of the swine DNA detection from the air collection during the grinding process. Only two positive results were detected, occurring at hour 3 in one collector at the 46m distance and one at the 91m range. No swine DNA was detected at the 137m distance.
Bioassay:
The PCR positive processed compost was placed into PRRSV and PEDV naive pigs to assess the infectivity of the virus detected. No PRRSV positive compost samples replicated to produce a PRRSV positive pig by serum PCR. Cornstalk biomass was negative for PEDV infection on bioassay. Woodchips provided the most PCR positive PEDV results by rectal swabs in the challenged pigs. As seen in Table 6, woodchip compost from day three and week two and the combination pile compost from week two produced a single PCR positive pig for PEDV on day four post-challenge, but all pigs were negative on day seven post-challenge. Clinical signs of diarrhea consistent with PEDV infection were observed in day 0, 2, and 4 pwf samples from the woodchips with multiple pigs in those pens testing positive by PCR. In the pen of pigs challenged with the week two combination biomass, one pig died from unrelated illness before the first sample collection.