Livestock owners urged to safely dispose of animal carcasses in flood aftermath

NOTE: In light of the recent Midwest floods, this is the fourth in a series of safe flood recovery stories to assist people in their recovery efforts. The series is produced by the Central States Center for Agricultural Safety and Health at the University of Nebraska Medical Center College of Public Health.
 
When an animal carcass decomposes, it provides an ideal environment for transmission and perpetuation of disease, which can potentially threaten both animal and human populations.
 
With routine livestock mortalities, disposal within 36 hours of discovery can significantly reduce risks of odor, flies and potential disease transmission. Burial, incineration, rendering, composting and landfill disposal are acceptable ways to handle a large animal carcass in most states.
 
While routine livestock losses are typically predictable and easily handled by farmers, managing significant losses due to a natural disaster or other unforeseen circumstance can be challenging. If accessing animal carcasses poses a problem for more than a few days, on-site disposal via composting or burial may be the only feasible options.
 
While both composting and burial are acceptable from a regulatory standpoint, so long as soil and groundwater conditions are favorable at the site, they may not be equally desirable in all situations. Amy Millmier Schmidt, Ph.D., associate professor and a livestock bioenvironmental engineer for the University of Nebraska-Lincoln and the Nebraska Extension, encourages farmers to consider composting carcasses rather than burying them.
 
“Burial can be a quick and effective way to dispose of animal carcasses,” she said, “However, it can be a challenge to excavate a deep enough pit to accommodate carcasses while still ensuring that the bottom of the pit is sufficiently separated from the water table.”
 
If a farmer has space and resources available to accommodate a mortality compost pile, Schmidt prefers this method for several reasons.
 
“With burial, there’s a higher risk of groundwater contamination, especially if the carcass is buried in water-saturated soil,” she said. “While composting requires more management by the farmer, it is less likely to contaminate water if it is properly designed and managed. It also allows observation of the process over time to ensure complete decomposition of the carcass and produces a finished material that has value as a soil amendment.”
 
When circumstances dictate that burial is a livestock owner’s best option, it is essential to avoid areas of sandy or gravelly soil. Burial sites must not be located in an area with a shallow water table. The excavated pit must be deep enough to accommodate the number of animals to be buried while ensuring that the bottom of the pit is located at least five feet above the groundwater table to reduce potential for decomposition liquid to leach into the water. It also should be deep enough for carcasses to be covered with four feet of soil before reaching the natural grade of the land.
 
“Contamination of groundwater is a legitimate concern following carcass burial, so published separation distances need to be observed. In Nebraska, burial pits must be at least 300 feet away from surface water sources, 500 feet from shallow aquifers, wells and residences, and at least 1,000 feet away from any public water supply well or primary highway,” Dr. Schmidt said.
 
It can be helpful to place at least 24 inches of carbon material – such as chopped straw or corn stalks, wood chips, etc. – in the bottom of the pit to help absorb decomposition liquids. Once carcasses are covered with soil to the natural grade, slightly mounding additional soil on top of the area can help avoid a depression forming once carcasses decompose.
 
Because incineration of a large animal carcass requires specialized equipment and a large amount of energy, it is generally not considered a viable or economical disposal option. However, for routine or emergency carcass disposal, incineration is acceptable.
 
“When and where it is available, rendering is a viable way to dispose of carcasses,” Dr. Schmidt said. “Unfortunately, this may not have been a practical option for many Nebraska livestock owners following the March 2019 flood.”
 
Landfill disposal policies will vary from facility to facility, but livestock owners may be able to dispose of animal carcasses this way.
 
Whenever possible, composting large animal carcasses is a safe way to allow a carcass to naturally decompose and break down into organic matter that can be incorporated back into the soil. In most instances, composting is a low cost and easy process.
 
“For routine mortality management, animal carcasses are usually composted in a windrow or bins,” Dr. Schmidt said. “If an animal carcass is isolated or can’t be moved, composting in place is possible.”
 
For windrow or bin composting, the compost site should have a base layer of at least 24 inches of carbon material to absorb the liquid produced by the decomposing carcass. Sawdust or other absorbent materials are recommended for the base. Wood chips can be used but may not adequately absorb liquid from the pile.
 
Liquid leaching from a compost pile must be contained to avoid runoff. Building the base large enough to provide at least 24 inches of space on all sides of the carcass will ensure that no part of the animal protrudes from the compost pile.
 
Once the base is prepared, and the animal is placed on top of it, the animal’s abdominal cavity must be punctured to avoid carcass bloat, which can rupture the compost pile. Between 24 inches and 36 inches of moist carbon material – an “envelope” layer – should then be placed on top of the carcass.
 
“The envelope layer material can be any kind of chopped substance such as corn stalks, wood chips or other forages,” Dr. Schmidt said. “Waste feed or plant material also can be used. If you don’t have any carbon materials like these, you can use solid manure. However, manure that does not contain sufficient carbon might slow the decomposition process. Ideally, equal parts of carbon materials and solid manure should be mixed, but any amount of carbon that can be mixed with the manure will ultimately benefit the composting process.”
 
During composting, microorganisms in a pile feed on carbon and nitrogen to grow and proliferate. This process generates heat, which drives decomposition and can kill pathogens in a pile. To insulate a pile and retain generated heat, cover it with at least 24 inches of dry carbon material.
 
“The top layer helps control odor and keep flies and scavenging animals away from the pile,” Dr. Schmidt said. “Don’t pack it on or that may seal off the oxygen to a pile and prevent it from composting effectively.”
 
Windrow composting is an option if a large number of carcasses must be composted or if no facilities are currently in place to perform carcass composting. The 24-inch carbon-based layer is required with a 24-inch perimeter around the windrow. Space between animals should be minimized with a layer of carbon material between them.
 
All abdominal cavities should be punctured and moist carbon material or manure should be used to provide at least 24 inches of cover on all sides of the carcass.
 
“We have found that a single large round bale provides about 100 cubic feet of carbon material,” Dr. Schmidt said. “It takes about four of these bales to create the base layer and cap necessary to compost an average 1,000-pound animal.”
 
TMR mixers can assist in chopping large amounts of carbon material for composting sites. If the carbon material needs moisture added, effluent from a runoff pond can be used to wet a compost pile. However, over-applying effluent or water to a pile can create runoff that must be contained and properly managed as a nutrient. Excess moisture also can impede oxygen from reaching the microbes that drive the composting process.
 
“Carbon material in the layer around the carcass should be wet enough that it clumps when squeezed in your hand, but does not produce excess liquid dripping from the squeezed material,” Dr. Schmidt said.
 
“Be sure to divert storm water from your compost site and contain any leachate or storm water reaching the pile to avoid any nutrient runoff,” Dr. Schmidt said. “Once a compost pile is prepared, it should sit for about 90 days if large animals are being composted. Smaller animals, like poultry or smaller cattle or pigs, may require only 30 to 60 days to compost.”
 
After 90 days, a bucket loader may be used to turn/mix the pile to stimulate a second heating and decomposition process. If no soft animal tissue remains and animals were not lost due to a livestock disease, there is no need to build the pile up again. Bones can be removed and disposed of via burial or in a trash dumpster and solids can be land applied at agronomic rates. If additional decomposition is needed, the pile can be mixed and re-formed, adding moisture only if the material is too dry to clump together when squeezed.
 
While many Nebraska livestock owners have likely taken care of animal carcasses resulting from recent severe weather, receding waters in some areas may reveal the need for more cleanup.
 
“If you discover an animal that’s greatly decomposed, but soft tissue remains, composting in place can be accomplished by covering the animal on all sides with at least 24 inches of moist carbon material and/or manure, followed by dry carbon material to a depth of at least 24 inches,” Dr. Schmidt said. “Up to 90 days of composting may be needed if significant soft tissue is present.
 
“Bones remaining following carcass decomposition should be buried or disposed of in a dumpster or through a landfill service. Bones may still attract scavengers and leaving them in the composted material when it is land applied may be unsightly and could even cause tire damage to vehicles when driving through the field.”
 
Additional carcass disposal information for Nebraska farmers is available through www.flood.unl.edu/livestock. Dr. Schmidt also advises livestock owners to consult the Nebraska Department of Environmental Quality for site-specific guidance.
 
“Dealing with animal carcasses can be very stressful, especially when a large loss occurs due to severe weather or other events,” Dr. Schmidt said. “We at Nebraska Extension are happy to do anything we can do to help Nebraska livestock owners work through this.”
 
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