Ensure you have plenty of carbon source material before beginning mortality composting. The amount needed for wooden bin composting can be estimated from the volume of the bin. For alternative bins made from wire, pallets, round bales, or other material, the amount will depend upon the diameter of the bin and height of the final pile. However, a rule of thumb is approximately 100 ft3 (3.5 yd3) or 4 to 5 tractor buckets of the carbon source mixture for each 100 lbs of mortality. If two or three carcasses are layered in a bin, the total will be somewhat less on a per animal basis as the base layer will be used for more than one carcass. However, too thin a base or covering layer of carbon source will lead to poor decomposition, excessive leachate, or odors.

Building the pile

1. Cover the base of the bin with a minimum of 18 inches (45 cm) of carbon source material as an absorbent layer to trap liquid leached from the carcass during composting. The base layer can be laid down several days prior to adding carcasses so that it begins to heat. This will speed up the initial stage of carcass decomposition.
2. Add a carcass in the middle of the base a minimum of 12 inches (30 cm) from bin walls or sides. Limbs may be tied or removed and laid next to the body if needed to keep away from bin sides.
3. If the bin is of sufficient size and two or more carcasses need to be composted, add a second carcass to the layer. Place adult carcasses back to back 8 to 10 inches (20 – 25 cm) apart and lamb or kid carcasses 6 inches (15 cm) apart with feet pointing to the pile’s edge.
4. Use a knife to lance the rumen. This provides access by microbes to the inside of the carcass and prevents the rumen from bursting due to gas build up from ruminal microbes. Additional cuts can be made on the limbs or torso allowing bacteria to enter, speeding up the decomposition process.
5. Add enough water to the surrounding carbon source to create a moisture content of roughly 50%. One to two 5-gallon buckets (40 – 75 liters) of water may need to be added per 100 lbs (45 kg) mortality. Adjust the amount depending on the dryness of the carbon source. Do not get the layer too wet. The carcass contains significant water and this must be considered when adding additional water.
6. Cover the carcass layer with 6 to 12 inches (15 to 30 cm) of carbon source material if a second layer of carcasses is to be added. If not, proceed with the covering layer.
7. A second layer of carcasses can be added as mortality happens. Scoop out a portion of the layer covering the first carcasses and lay fresh carcasses on top. Maintain at least 6 inches (15 cm) between layers. Lance the rumen and add additional water as needed. If composting in deep wooden bins, complete layers in the back before beginning to compost in the front area of the bin.
8. After all carcasses have been added, top off the pile with a minimum of 18 inches (45 cm) of carbon source material creating a cone shape to shed rainwater if no roof or tarp covering will be used.

After a couple weeks, the pile will have shrunk and additional carbon source may be added to the covering layer. Check the pile occasionally to ensure animals have not disturbed it and that no portions of the carcass are visible. Also, check for noticeable odors and pile temperature.

Heat cycles and aereation

First heat cycle

Mortality compost piles should undergo two heat cycles, the first phase after building the pile, and a second phase that occurs after turning the pile. After building the pile, bacteria will be working and generating heat. After three or four days, pile temperature should reach over 131°F (55°C) and remain at that temperature for up to two weeks or longer before beginning a gradual decline. This heat is important to speed up decomposition and to reduce pathogens. Pathogens are destroyed due to the combination of pile heat and length of exposure. For this reason, it is important to monitor pile temperature. This need not be done daily but at a minimum temperature should be checked every three to four days.

The first heat phase continues until pile temperature begins to drop. By this time, all flesh and soft tissues will have decomposed and mainly large bones are left. In a well-working pile containing carcasses of adult animals, this occurs in roughly 10 weeks. Lamb and kid carcasses may take only a few weeks for soft tissues to decompose.

Turning compost piles (aereation)

When the temperature of the pile decreases to near ambient temperature the pile can be turned. For composted adult goat carcasses, after 75 days the pile can usually be turned; composted young animals can be turned more quickly. Use a tractor bucket to pick up material and either dump it back on the pile or into a secondary bin. Allow the material to fall from the bucket onto the new pile. This aerates the pile and mixes the contents. Use additional carbon source material to ensure enough covering layer is put on the turned pile. This will insulate the pile and trap any odors generated. Moisture can be added if the pile is too dry or the pile can be allowed to dry if it is too wet, from trapped rainfall, for example.

Although turning compost piles speeds up the process, the decision to turn piles will depend upon the producer’s reasons for composting and available equipment. If a producer wishes to create compost for use on pastures, turning piles to initiate a second heat cycle and speed up decomposition is best. If a producer composts to have a lawful means of carcass disposal and is not interested in rapidly creating compost, turning is optional. This would also be true of producers who may not have machinery to easily turn mortality compost piles. Piles left unturned, called static piles, will continue to decompose, only at a slower rate.

Second heat cycle

After turning, the pile will heat again and reach temperatures over 131°F (55°C). This is important in pathogen reduction as in the original pile not all parts may have reached high temperatures for a sufficient length of time. Redistributing pile contents via turning increases the probability that all portions of the compost will heat sufficiently. Monitor temperature of the pile as it heats. Temperatures over 131°F (55°C) should be sustained for several days or a week or more in the second heat cycle. The second heat cycle should take approximately the same length of time as the initial cycle. After a second 75-day period, the compost pile can be left to cure for several weeks before use. Any large bones left at this time should be added to a future compost pile for further break down.

Bones

During the first heat cycle most small bones will be degraded. When turning the pile, collect larger bones and place them in the pile center. At the end of the second 75-day period, these should be brittle and break easily. Those that are thicker, skulls for example, can be placed in a new compost pile to decompose further.

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