Mortality Composting

Note: First seen in Progressive Cattleman magazine April 2016
Mortalities are an unfortunate reality for livestock operations. Whether they’re caused by disease or natural disaster, losses of livestock occur for both confined and pastured animals and these mortalities must be managed responsibly to protect both the environment and the health of other animals. While every livestock producer likely has a method or two available to dispose of routine mortalities, developing a Mortality Management Plan can help a producer think through the options available to facilitate prompt and biosecure disposal of livestock that are lost due to unforeseen circumstances like inclement weather or disease. Oftentimes, discussion of mortality disposal is focused primarily on confined livestock where disease transmission can be more prevalent and natural disasters can have a major impact due to stocking density of the animals. However, pastured livestock like stocker cattle and cow-calf pairs are subject to losses from natural disasters and diseases, too. The recent severe winter storm, Goliath, proved deadly to thousands of pastured cattle that were buried alive by excessive snowfall from the Texas-New Mexico border through the Midwest. A similar storm, Atlas, dumped rain and snow accompanied by high winds and rapidly falling temperatures on the upper Midwest in the fall of 2013 leaving several thousand pastured cattle dead. Losses of this nature are often particularly difficult to manage because of limited accessibility to the animals, potentially for several days.

While individual state regulations can vary, most states allow for disposal of dead animals via several methods including burial, rendering, incineration, composting, and landfilling. Incineration is often expensive and requires air quality permits in many states. Though burial can be convenient, it can present a risk of groundwater contamination in some regions depending on soil type and depth to ground water. When animals have been lost due to disease, there is additional concern that burial will not provide a way for the disease-causing organism to be rendered inactive, presenting a risk of disease reoccurrence. Rendering continues to be a commonly used method for disposal of livestock; however, rendering facilities in some regions are becoming less accessible and livestock lost due to diseases like porcine epidemic diarrhea virus (PEDV) and highly pathogenic avian influenza (HPAI) may not be collected by renderers due to disease transfer concerns. Composting is an effective means of mortality disposal that can be done on any size livestock operation with any size animal and most farms are already equipped with the necessary materials and implements to construct and manage a compost pile. Whether used for routine disposal or a catastrophic loss, composting can be a viable option on most livestock farms. While the sheer volume of animals lost during some catastrophic weather events makes disposal by composting or any other method challenging, the value of planning for such events that one hopes will never happen cannot be overstated. Knowing ahead of time how and where to obtain carbon material for large-scale composting, who to contact for assistance, and how to establish compost piles can help make the disposal process more manageable if the need arises.

Research at a number of universities has shown that animals of any size can be composted – with one east coast university even composting a beached whale! Demonstration sites in Nebraska organized by USDA-NRCS and the University of Nebraska have demonstrated successful composting of mature cattle, calves, pigs, and horses. Most people will say that the key to composting mortalities is to provide the necessary carbon, nitrogen, and moisture to facilitate the decomposition of the pile materials by microorganisms. While this is certainly true, having someone dedicated to the success of the composting process is equally essential! Routine monitoring to make sure the pile is heating up and to make adjustments if a problem is identified is critical – especially when first beginning to compost.

Constructing a pile with adequate carbon material is essential to feed the microbes responsible for driving the compost process and to retain heat, minimize odor, and discourage scavenging animals from disrupting the pile. As a general rule, a layer of dry carbon material 24 inches deep should form the base for a mortality compost pile. The base should accommodate the carcass(es) while leaving at least 24 inches of space between the animal(s) and the edge of the pile. Once the animals are in place, additional carbon material should be added to cover the animal(s) on all sides to a thickness of 24 inches. No part of an animal should protrude from the pile or odors and scavenging animals will likely be an issue. Moisture is also essential to the composting process and may need to be added depending on the moisture content of the carbon source used. The goal is for the material around the animal to have a “damp sponge” feel. It should clump when squeezed but water should not drip from the hand. Material that is too dry should have water added during the pile building process; throughout the cycle additional water can be added to the top of the pile. Material that is too wet should be mixed with dry carbon material to reduce the overall moisture content.

When disposing of animals lost to severe winter weather where frozen ground may make burial impossible and movement of mortalities to a central location may not be feasible due to excessive snow, extremely muddy conditions, or even carcasses frozen in place, composting in place is recommended. Though not an ideal pile design, simply covering the animal with 24 to 36 inches of moist carbon material may provide enough insulation to allow heat to be generated by the microbes responsible for driving the composting process. In some cases, soil or snow from the area surrounding the animal may need to be used as a cover for the pile to provide additional insulation and moisture. While soil can be used as pile cover material when other options do not exist, “sealing” a pile too well with soil can impede air flow within the pile and negatively impact the composting process. Therefore, only a thin layer of soil – perhaps 4 to 6 inches – should be used in a situation like this when it is needed to provide insulation or to hold carbon material in place under windy conditions.

Most farms with confined livestock will have the necessary material available on the farm to construct a pile, while pastured systems may need to identify sources of carbon material for the pile. Manure, chopped forages, chopped corn stalks, waste feed, and wood chips or shavings all make good compost pile ingredients. A front-end loader or tractor with a scoop can be utilized to move material and animals to the pile, to build and turn the pile, and to remove finished compost for land application. It is important to keep in mind, though, that proper washing and sanitation of equipment used for animal movement or pile management should follow each use, particularly if losses occurred as a result of a disease.

The length of time required to completely compost an animal is dependent on the size of the animal(s) and, to some extent, weather. While small pigs or poultry may compost in a matter of two or three months, larger animals will require three to six months for each of the two recommended compost cycles. Likewise, although an animal will begin to compost quicker when warm temperatures support the pile heating process, frozen animals placed in a new compost pile during winter weather have been successfully composted during research and on-farm trials when sufficient carbon material was used to construct the pile.

Temperatures should rise to approximately 130°F at the core of the pile within a few days of a new pile being established and should stay at this temperature for several days or weeks. Compost piles can begin to generate heat very quickly even during cold winter weather if the microbes have the appropriate carbon, nitrogen, and moisture to survive and thrive. A long-handled thermometer is ideal for monitoring pile temperature, but at a cost of over a hundred dollars, may not be practical for most farmers. Without a thermometer, the manager will need to focus on identifying foul odors or other visible issues and addressing the cause of the problem (pile too wet, animal parts exposed, insufficient pile cover material, etc.). The determination of when to turn the pile to begin a second compost cycle will need to be based upon recommended timeframes for composting the animal based on its size. For those monitoring pile temperature, piles should be turned once the core temperature falls below 120°F.

Research has revealed that composting can successfully inactivate most disease-causing organisms. Recent research at the University of Nebraska led by Dr. Amy Millmier Schmidt in collaboration with faculty in the UNL School of Veterinary Medicine and Biological Sciences has shown that composting is an effective and biosecure method for disposal of PEDV-positive swine mortalities. Likewise, on-farm poultry composting has been successful for disposal of catastrophic poultry losses due to Avian Influenza. For cattle, as well, bacterial and viral disease-causing organisms can be inactivated during composting.

Preventing water contamination and ensuring farm biosecurity should be of utmost importance when managing manure and mortalities no matter the size of your livestock operation. Information about choosing an appropriate site for composting, pile design and management, nutrient value of compost, cost-share opportunities, and biosecurity considerations was recently presented at a UNL Mortality Composting Demonstration Event and is available through the Nebraska Extension Animal Manure Management Team’s website at manure.unl.edu. In addition, anyone wanting more information about mortality composting can contact Dr. Amy Millmier Schmidt at aschmidt@unl.edu or (402) 472-0877.

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