South Dakota State University professor and Extension swine specialist Bob Thaler is currently working on a research project he hopes the U.S. pork industry never has to reference — how to effectively dispose of carcasses infected with a foreign animal disease from a commercial swine production unit without contaminating the environment and further spreading the disease.
"We think we're safe with the borders of the Atlantic and Pacific oceans, but when you take a look at what's happened in the Philippines, East Timor, which is right by Australia, we can't guarantee that, so it's certainly a possibility," Thaler says. "When you think about it logistically, if it hits, the two big issues that we have to deal with is first how do we euthanize millions of animals in a humane way and then secondly, how do you dispose of those carcasses, where we are not contaminating the environment and increasing the spread of that."
During the SDSU Swine Day this week in Brookings, Thaler shared the latest updates on an above-ground burial research project — a project that came to fruition after industry input at last year's Swine Day event. Above-ground burial composting involves digging a two-feet-deep trench, laying down 20 to 24 inches of organic matter, such as wood chips, and then placing the animal mortality on top of that and filling the trench with dirt. Previous research had been done in this area by Gary Flory at the Virginia Department of Environmental Quality, but nowhere near close to the climate and commercial conditions of the Midwest.
Thaler, along with Flory; John McMaine, assistant professor and SDSU Extension water management engineer; Amy Schmidt, assistant professor at University of Nebraska-Lincoln; and Diego Diel, formerly at SDSU and now associate professor at Cornell University, began their 2 x 2 factorial design trial this past June to see how effectively the compost pit would work in a South Dakota summer and winter. Each pit was dug 8 feet wide, 60 feet long and 22 inches deep. For organic matter, they decided to test wood chips as well as corn stalks, since South Dakota and most states in the Midwest would more likely have an abundance of stalks than wood chips during an FAD outbreak.
Research parameters included carcass temperatures, water samples at 6, 18 and 36 inches for nitrates, bacteria and Seneca Valley virus, and visible carcass decomposition. Each of the three well poles that were placed in the pit to collect water were sealed with bentonite so no leaching could occur along the well pipe.
All 88 carcasses (44 carcasses per pit) for the research project were market weight pigs. Once the carcasses were placed in the pit, thermal probes were placed in six body cavities.
After much industry input, the researchers decided SVV as the virus of choice to test in the pit. Twenty-four feeder pigs from SDSU's swine unit were challenged with SVV, euthanized and then wrapped in netting. Six sets of two pigs were placed within one meter of each test well and then all the pits were covered with dirt. The pits were surrounded by cattle panel fence and a game camera was set up to monitor for predators.
Each month for six months one set of mortalities per pit was tested for SVV through polymerase chain reactions. To do this, the researchers collected tissue samples from the tonsil area as well as the abdominal cavity of the carcasses. Monthly water samples were also tested for SVV, and three temperature carcass probes from each pit were also entered into the data logger.
As the composting process began, Thaler noted that carcass decomposition didn't happen as quickly as he had originally thought, and the pit smell resembled more of a septic tank odor than anything else. He also found that the wood chip mortalities appeared to not decompose as fast as the mortalities placed in the corn stalks.
"When we looked at the carcasses, basically they were about 25 PCR positive — the lower the number, the hotter it was and as we went through time, we can see that those numbers rose up, which means there was less virus there," Thaler says. "But in each of these cases it appeared that the virus was more in the wood chips than the corn stalks, and again, indicating that there's some kind of more breakdown happening in those corn stalks."
When it comes to the water sample testing, Thaler says the results were both positive and negative.
"When we analyzed those water samples, we found SVV in the wood chip pits in three different places and one of the corn stalks early on, so kind of good news, bad news," Thaler says. "Bad news is we found that in there, but the good thing is though, they were only at the 6- and 18-inch wells. Nowhere at the 36-inch wells did we find any SVV infiltrating there."
The carcass temperature readings were not as hot as the researchers had expected, with the mortalities in the corn stalks averaging around 22.8 degrees C and the mortalities in the wood shavings at 21.8 degrees C.
"If you look at average temperature, basically the corn stalks are about a degree Celsius higher than wood chips and again, maybe that's why we have a little more breakdown," Thaler says. "The question is then how hot is hot enough or how high does it have to be to inactivate those viruses?"
Thaler notes it was and unusually wet summer for South Dakota so if the virus was going to spread through the water, this would have been the year for it.
"You can look at it from the standpoint, if we're ever going to get any infiltration through the water profile, it's going to be in a year like this," Thaler says. "Our soil is saturated. We're getting rain every week. If the virus was going to go through it, now's the time that's going to happen. We saw some, but not down at the 36-inch and out level."
Thaler believes that the extra moisture is also one of the reasons the composting didn't happen as fast.
"Compared to regular composting, we had organic matter in the bottom and dirt on the top, so I think that was limited versus organic matter all the way around the animals," Thaler says. "For composting to work and those of you that have composted under operations, you've got to have the right moisture content for that to work. Especially in our wood shavings, when we dug into our wood chips, you're stepping on water, so I think it was too wet for that to really compost."
The water and tissue samples that did test positive for SVV will now be sent to the lab to conduct a bio-assay to see if the virus is infective.
Thaler and McMaine are also beginning their second phase of the research project this month to test how effective above-ground burial composting is in a South Dakota winter. While the first phase of the project provided some useful information on how efficient pits are in preventing the spread of a virus, Thaler recognizes above-ground burial won't be an easy feat for any commercial operation during an FAD outbreak.
"Those pits were 8-feet wide, 60-feet long with 44 pigs," Thaler says. "If we had to get rid of 2,400 carcasses from a 2,400 wean-to-finish barn, it's going to take 48 pits that size, so again, we know we need to do a lot more research in this area, and again, we pray that this is something we will never need."
This trial is supported by Minnesota Pork, the South Dakota Pork Producers Council, the Iowa Pork Producers Association, Nebraska Pork Producers Association and the South Dakota Soybean Research & Promotion Council.