Growing Beef Newsletter
February 2025, Volume 15, Issue 8
Mortality composting - an option for producers when livestock turn into dead stock
Tony Mensing, ISU Extension and Outreach agricultural engineer
Cattle producers provide high-quality care for their livestock, but even with the best efforts, some death loss within the cattle production system is inevitable. It definitely is a somber subject, but not one that can be ignored. Having a plan for how to manage mortalities is important for producers so when a loss happens, it doesn’t lead to a scramble situation. Composting is one way to deal with the carcass of a deceased critter, and while it might not be the best for every situation it certainly can have some distinct advantages in a lot of cases.
Regulations in Iowa require that dead livestock be disposed of as soon as reasonably possible which is generally considered to be within 24 hours of death. This emphasizes the importance of having a predetermined plan. Alternatives to composting include rendering, incinerating, and burying, each of which comes with its own set of drawbacks. In a quick initial comparison to these alternatives, composting can be accomplished without needing outside service vendors, without having to purchase an engineered incinerator, and without having to dig through frozen soil. It does, however, take some oversight throughout the composting process, where the alternatives are generally completed in a single step without needing much follow-up. No matter which option is implemented it is important to follow all applicable rules and regulations.
In general, composting can be partly science and partly art. Management of the process is based on the objectives. In this situation the goal is to properly dispose of a carcass rather than truly optimizing things for efficient production of compost as a soil amendment. In either case, the same transformation is happening, microbes are consuming and decomposing the compost ingredients. The microbes that make the composting magic happen need carbon, nitrogen, moisture, oxygen, and some temperature regulation. Simple enough in the broad sense, but the finer details of these requirements are the difference between successful composting and creating a rotting mess. At the beginning of the process, carbon and nitrogen ingredients should be at a ratio of 30 parts carbon to 1 part nitrogen, moisture should be about 50% by weight, oxygen should be above the 5% level, and temperature should be in the range of 130 to 150 degrees Fahrenheit.
The great news is that for the purposes of mortality composting the detailed requirements and overall process offer a lot of leeway. Successful carcass composting can be accomplished relatively easily if the composting pile or windrow is constructed properly when initiating the process because the microbes do the actual work!
The 30:1 carbon-to-nitrogen ratio is achieved by using a high carbon base and cover layers for the pile to envelope the high-nitrogen carcass. High-carbon materials for composting are sometimes referred to as browns. Wood chips and corn stover are common examples, and they will have a much higher carbon-to-nitrogen ratio than 30:1. These carbon sources are relatively low in moisture content, where the carcass itself will be over 50% water. By surrounding the high moisture, high nitrogen carcass with the lower moisture, high carbon source, the composting microbes can be active at the interface between the two different materials and essentially will manage themselves to the needed 30:1 carbon to nitrogen ratio and 50% moisture level if their oxygen and temperature requirements can be met.
The air in our environment is around 21% oxygen so the microbes’ demand for oxygen can be met just by allowing some natural air to permeate the pile. The temperature range needed is certainly warmer than our winter months, and at over 130 degrees Fahrenheit, it also is warmer than ambient conditions during the warmer seasons, but the microbes can manage this themselves, too. Their process of decomposing the carbon and nitrogen materials generates heat. So, if the pile or windrow insulates them from the cooler ambient conditions, they will create enough heat energy to work up to the appropriate temperature range. While the scientific requirements may seem daunting at first, the process really is forgiving if it is set up well at the start.
Getting the mortality composting pile or windrow constructed properly is the most important part of the process.
- Start by identifying a suitable area that doesn’t receive additional runoff water from precipitation events and is accessible for the heavy equipment needed to handle the composting materials. Keep in mind that the process can take 6-12 months for large cattle carcasses.
- When an appropriate location is found, place a base layer of high carbon material at least a couple of feet thick that’s also wide enough and long enough to allow 12 to 18 inches of perimeter buffer beyond the carcass when it’s laid on its side on top of the base. If a somewhat sturdy base material such as wood chips is available, that can be a great choice because the base should maintain some pore space between the individual pieces of carbon material to help allow air infiltration. Other brown high-carbon materials such as cornstalks can be used successfully, but it is important to provide them in an adequately thick layer that isn’t so finely ground that the weight of the carcass, along with the moisture it releases, will compress them to the point of eliminating those important pore spaces.
- After the base is laid out the carcass can be placed on it. It isn’t required that the carcass be dismantled or pierced but either or both can reduce the overall amount of time the composting process takes.
- Cover the carcass with a peaked mound of carbon material such as corn stover. The cover should be at least 12 to 18 inches. Some pore space is important but structural integrity is not as critical as it is in the base since the carcass weight and water won’t be compressing it. It may be necessary to top off the pile within the first few days of composting if the initial yielding or let down of the carcass causes the peak of the mound to become concave.
- The pile should be maintained so that it sheds precipitation rather than collects it. Approximately 5 cubic yards of carbon material will be needed per 1,000 pounds of carcass. If multiple mortalities are to be composted a windrow can be created, essentially adjoining piles linearly end to end.
After the initial construction of the pile the process should primarily just need monitored. It is important to ensure that the pile is maintained in good condition to shed water, cover over the carcass remains adequate to prevent scavenger animal activity, no leachate is being produced, and the pile is relatively odorless. A long-stemmed thermometer, approximately 48 inches long, can be handy for monitoring the internal temperature of the pile providing reassurance that the microbes have been provided with appropriate conditions to do their job.
If any adverse conditions are observed, they need to be corrected. For example, if there is a strong offensive odor from the pile something is wrong. In that case it is likely that the process has gone anaerobic, meaning not enough oxygen is being provided for the desirable microbes. That can result from the carbon base material not having enough pore space to allow ambient air to permeate the pile as the warm air from the microbes rises and is exhausted out the top of the pile, or from having too much moisture in the pile taking up the spaces where air should be able to move through.
After an identified issue is rectified, the composting process will continue. The pile will start off cooler than the 130 to 150 degrees Fahrenheit level, but through the first few days of the process it will warm, and then as the materials get used up by the microbes, the temperature will eventually begin cooling off. During the warmer part of the year after the process has heated once and the internal temperature begins to cool, the pile can be “turned” or mixed. Material handling forks can be inserted and lifted through the pile which will mix some of the remaining high carbon and higher nitrogen material as well as rebuild some of the pore space structure. This mixing will jump-start a second heating process, refining and making the final product more consistent.
Composting as a tool for mortality management isn’t the only method available, but it certainly is one with lots of positive attributes and deserves consideration as producers review or put together their plan for the inevitable periodic loss from their operation. While composting is scientific and happens in a somewhat narrow range of conditions, the microbes want to do the work and will essentially manage themselves if they are given the right start, and producers can use a touch of art in monitoring the process.
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