Composting Cows

Dr. Clell V. Bagley, D.V.M.
USU Extension Veterinarian

During the time of the “anthrax in the mail” incidents, I received a call from a concerned homeowner in rural Utah. A cattle operation near him has always just dumped their dead animals in a wash, near their operation, but also near his home. He had complained before about the odor and flies but now was concerned about anthrax. I explained that we do occasionally have some anthrax in Utah but in the situation he described, this was not an actual threat to him. He accepted that and the issue of anthrax was resolved but the issue of flies, odor and other disease potential continued.

The disposal of carcasses of dead cattle has become an increased concern for producers, veterinarians and the public. Rendering facilities have become less common and pickup fees more expensive. Regulation has increased for other methods of disposal. The regulations for your specific area can usually be found through your local public health office and the Utah Department of Agriculture and Food. In 1999, the USDA/EPA regulations for AFO’s and CAFO’s began requiring an approved plan for disposal of animal mortality, in addition to a plan for management of animal waste. Consider all the disposal options available to you including rendering, burial, and hauling to the landfill. Another method that some producers in Utah and elsewhere are using is composting of carcasses, also defined as “above ground burial in a biomass filter.”

Composting of poultry carcasses began in the 1980’s and was later adopted and used by the swine industry. It has not been used extensively for disposal of large animals but recent changes have encouraged both researchers and producers to begin looking at it as another alternative for disposal. Composting is recommended by EPA as one of the better methods for disposal of both carcasses and manure. If managed properly, there should be no odor, fluid leakage, flies or attracted scavengers. But, composting of adult cows or horses presents a special challenge because it concentrates such a large amount of tissue in a small area.

The composting of carcasses must usually occur on the property owned by the producer. The resulting compost product usually must also be used on the owner’s land and on land that is not used for human food production.

Composting can destroy many disease causing agents, but not all spore forming bacteria. It is not yet known if composting will destroy the prions of TSE diseases, such as BSE or Mad Cow Disease. Research is currently underway in the U.S. and Canada to answer that question. Prions are very resistant to heat and many chemicals. They are also resistant to some enzymes but may be vulnerable to those present during the composting process.

Composting of carcasses is controlled decomposition with microorganisms metabolizing the organic products present in the carcass. The microbial population uses the carbon products as an energy source and the nitrogen products for their protein synthesis. This process gives off water, carbon dioxide and heat. The process of decomposition of the carcass is anaerobic. But, as liquids and gases move away from the carcass into the co-compost material, they enter an aerobic zone. There these products are trapped and further degraded to carbon dioxide and water.

The co-compost material must serve as a biological filter to trap organic gasses and prevent their smelly escape into the surrounding environment. If offensive odors are evident, something is wrong with the process. The carbon to nitrogen ratio may be out of balance or the pile is too wet or the particle size is too large or small, etc. A practical guide is the “nose and shoe” test. If there is odor or fluid leakage from the pile something is wrong and needs to be corrected. In this case the compost pile will also likely attract scavengers and flies.

Much of the literature on general composting discusses the importance of having a consistent pile. But, in composting animal carcasses there is definitely an inconsistent pile. There is the composting material and then there is the carcass buried inside of it. This arrangement becomes more “consistent” when the pile or windrow is eventually turned, mixed and then allowed to continue the composting process.

Selection of the co-compost material is an important decision. The material chosen determines the carbon to nitrogen ratio, a critical factor in composting (25-35:1 is needed). Wet hay and wet manure have not worked. Green sawdust is usually listed as the preferred co-compost. However, straw, shavings, rice hulls, paper, silage, leaves, manure screenings, corn cobs, manure and straw mix, and a mix of manure and sand have all been used with reasonable success. The key is observation and management to adjust to the specific situation.

Aeration is also a critical factor for composting and is determined primarily by porosity, or the size of the co-compost particles. Each co-compost used will require some trial and error efforts to learn how to manage it. Chopping of straw will usually improve its use. Any change to a different co-compost will also involve a learning period on how to make it work. Addition of water may be necessary, but don’t add so much at one time as to create a leaching effect. The co-compost itself should have a moisture content of 40-60%.

A bin system, as is used for poultry and swine, could be used for one or two large animals. Or, large bales of hay or straw could be used to create a bin. A cover over the bin or pile would be helpful for areas with high precipitation rates, but this is usually not a problem in Utah. A composting windrow 10-12 feet wide and 6-7 feet high can also be used and can be extended as far as needed to accommodate carcasses.

Provide a base of at least 1-2 feet of co-compost material (2 feet for an adult large animal), put the carcass on it, perhaps wet the carcass slightly if it and the co-compost are very dry, cover so there is another 1-2 feet of co-compost over the carcass and wet that slightly if needed. If there is leaching of fluids from the pile, it needed a deeper base, was too wet, or too much water was used. Confine and absorb these leaching fluids with other co-compost and then put this mix into a composting pile. If odors are escaping, a deeper coverage with the co-compost may resolve that problem. But, the pile or windrow may be too wet inside or the co-compost may not have provided enough carbon.

It is usually considered best to puncture the rumen and to open the thoracic and abdominal cavities of large carcasses. This will increase the surface contact area and speed up the decomposition and composting process. But, some producers have had good success with no carcass preparation. The carcass has just been laid on the co-compost pile and covered. That is certainly the easiest method.

The site for composting should be accessible, even in wet weather, and provide rather level ground to avoid an influx or an outflow of water from precipitation. A hard surface such as concrete or asphalt is ideal but not essential. A plastic cover can be placed over the ground and under the composting site, but this plastic may complicate the turning of the pile or windrow. The hard surface or plastic liner may be essential and required in areas with high water tables to prevent leaching into the groundwater.

A three foot long stem thermometer should be used to monitor the progress of the composting process. The internal temperature of the compost pile is a good indicator of the current biological activity. Take and record daily temperature measurements at one and three foot depths. The temperature should reach 135-145o F and stabilize there for a few days to weeks.

Usually the carcass compost pile should be turned after 3-4 months and allowed to continue the composting process for another 3-4 months. Be sure to get all the animal parts and pieces re-covered. Then the compost should be ready to apply to land and work into the soil. Any pieces of bone remaining (even large ones) should be brittle and weak and will usually break apart during the spreading process. Some of the finished compost can be used in the next cycle of carcass composting as up to 50% of the co-compost mix.

For successful composting of the carcasses of large animals:
  1. Be a good observer willing to adjust and correct problems.
  2. Use a thermometer and keep records.
  3. Check for fluid leaching and confine and absorb it with co-compost material.
  4. Check for odors and if present, add more co-compost or water, or dry out the pile with aeration, if needed.
  5. If necessary, re-start the whole process with a different type, quantity or wetness of the co-compost material to get the odor, flies and leaching under control.
An excellent guide on composting in general and with specific information on composting of animal carcasses is available for purchase : Field Guide to On-Farm Composting. Natural Resource, Agriculture, and Engineering Service (NRAES) 114, 1999. Cooperative Extension, 152 Riley-Robb Hall, Ithaca, NY, 14853-5701; phone 607-255-7654; Web site: WWW.NRAES.ORG