The overall objective of this project was to determine whether or not the Above Ground Burial (AGB) system is a practical solution for pork producers in the Western Cornbelt for mass burial in the event of a catastrophic FAD, or in times of packing plant shut-downs, as was experienced in 2020 due to covid-19. Key indicators were:
- What is the rate of market hog carcass decomposition at 6 & 12 months?
- Is decomposition rate affected by carbonaceous material used and season of the year?
- Will there be leaching of the fluids from the swine carcasses?
- What are the temperature levels and durations of the mortalities throughout the year?
- Will Seneca Valley Virus (SVV), a sentinel virus for African Swine Fever, be rendered inactive in an AGB system?
The trial began in June of 2019. We dug 5 pits, with each pit being 8 feet wide, 60 feet long, and 22 inches deep. Test wells were put in each pit at 6″, 18″ and 36″ below the bottom of the pit. Two pits were used for the June burial, two pits were used for the November burial, and one pit was used in August to compare intact vs opened carcasses. All the carcasses used in the June and November burials were sliced open because they were transport mortalities from a packing plant, and the USDA inspectors required the carcasses to be denatured before they could leave the premise. For both the June and November burials, one pit was layered with 22 inches of wood chips and the other pit was layered with 22 inches of corn stalks. Forty-four market weight mortalities were placed in each pit with temperature probes inserted into the carcasses. Twenty-four feeder pigs were challenged with Seneca Valley Virus (SVV), euthanized, and placed in the June pits. After that, all carcasses were covered with 24″ of fill dirt. Each month, 2 feeder pig carcasses were dug up and tissue samples, carbon sources, and pit water samples were taken for SVV analysis. Monthly water samples were analyzed for SVV, nitrate-N, and E. coli concentrations. An add-on to the project was a bioassay where SVV-free weaned pigs were challenged with either tissue, water, or carbon samples that tested PCR-positive for SVV in order to determine whether or not it was an active virus.
Temperatures of the carcasses were higher than both the soil and air temperatures, but were not as high as reported in other trials. We believe a major factor contributing to this was that 2019 was one of the wettest summers in Brookings, and the mortalities were too wet for optimum composting breakdown. As expected, carcass temperatures from the June burial were higher than that of the November burial, and there was more breakdown of the June carcasses since microbial activity decreased as temperatures dropped. It took until summer of 2020 before the November burials reached maximum temperatures. For both seasons, carcasses placed on wood chips had higher temperatures than those placed on corn stalks. When comparing intact vs opened carcasses, the intact carcasses reached higher temperatures than the opened ones.
Carcass decomposition was assessed monthly by visually appraising the carcasses when the SVV-challenged pigs were dug up. While there was not a numeric scale, mortalities placed on corn stalks were typically more decomposed than those of carcasses on wood chips.
Water samples from the wells in the pits indicated relatively high nitrate-N concentrations soon after placement, but those levels decreased over time. Nitrate-N concentrations were greater in the corn stalk pits (10 ppm) versus the wood chip pits (5 ppm), but this is another indicator that there was more carcass breakdown in the corn stalks pits. E. coli concentrations were highly variable (0 to 18,000 CFU/100 ml) and were not different between treatments or well depth. As expected, E coli numbers were lower in cold months as decomposition and microbial activity decreased. While the levels observed are higher than the levels recommended for recreation water quality (235-575 CFU/100 ml), they are substantially lower than the concentrations found in swine manure (770,000 CFU/100 ml). While we had expected the numbers to be lower, the excess rain reduced composting activity and subsequently temperature, so it wasn’t hot enough to have more E. coli breakdown. These results indicate that care should be taken to prevent leaching of E. coli over sensitive aquifers. From an E. coli risk perspective, it is not recommended to use above ground burial in areas with sandy or loamy soils with a high hydraulic conductivity, a high water table, or a sensitive aquifer. Also, summer burial is preferable to jumpstart decomposition prior to any significant downward water movement through the soil.
Seneca Valley Virus was detected in the water samples, but only from the 6″ and 18″ wells. No SVV was detected from water from the 36″ wells. Also, only one water samples from the corn stalk pit (18″) tested positive for SVV while 10 samples over 11 months from the wood chip pit tested positive for SVV. It should be noted that SVV was detected in the July 2019 through November 1, 2019 testing, but no others after that through the May 2020 sampling. Seneca Valley Virus was detected in the carcasses of the challenged feeder pigs, and in the carbon source and water surrounding them. However, the SVV concentrations were lower in the carcasses on the corn stalks versus the wood chips. Since we used PCR testing to determine the presence of SVV, we didn’t know if it was a live virus, a dead virus, or just a piece of the virus. In order to determine if it was a live virus, we did a bioassay where we challenged SVV-free weaned pigs with the PCR-positive material, and none of the animals seroconverted. That is great news because it means that AGB inactivates or destroys SVV.
Finally, the wells and thermal probes were pulled in March of 2021, and the ground farmed that year. After fall harvest, you cannot see where the pits are (See Appendix).
I believe these results are fairly positive for the swine industry for several reasons. First, even when there is excessive rain, decomposition still occurs, and corn stalks are a viable carbon source to use for Above Ground Burial. We’d expect that in “normal” rainfall years, decomposition and temperatures would be higher. Secondly, even though there was leaching of nitrate-N, E. Coli, and SVV into the test wells, it decreased over time. Thirdly, the SVV detected via PCR in the water and carcasses was not infective so that means aquifers won’t be contaminated. Finally, from an agronomic standpoint, 2 years after burial the ground can be returned to normally farming practices.