Mortality Composting

Composting of animal mortalities and slaughterhouse waste uses naturally occurring microorganisms to breakdown organic matter under controlled conditions. It creates a product that can be used as a soil amendment, providing organic matter and nutrients.

Composting is an approved method for disposal of dead livestock on Ohio farms. However, before this method can be use, a two-hour Ohio Animal Mortality Composting Certification Course must be completed.

Benefits of composting to dispose of mortality include:
-  Cost-effective and easy to accomplish
-  On-farm disposal
-  Pathogen destruction
-  Environmentally sound
-  Nutrients recycled

To be effective, mortality composting must:
-  Protect ground and surface water
-  Maintain air quality
-  Reduce risk of disease transmission
-  Control flies, vermin, and scavenging animals

The method of composting mortalities differs somewhat from other composting systems. First a base layer of woodchips or other carbon amendments is established, then the animal is laid on top and covered with more amendment. During composting, the temperature will increase due to microbial activity. The highest rates of decomposition occur in the range of 110-150°F and temperatures above 131°F for 3 days will kill parasites and pathogens.

The figure below illustrates the flow of materials in animal mortality composting.

The animal carcass and carbon amendments can be layered in a windrow, bin, or static pile. The two-hour certification training program covers how to size a mortality composting system, determine the amount of amendment that will be needed, and determine length of time in the primary and secondary stages. The sections below provide a brief description of best practices for composting animal mortalities.

REMINDER: Before composting can be used to dispose of dead animals, the Ohio Animal Mortality Certification Course must be completed.

Laying a base: A layer of amendment, such as sawdust, woodchips, chopped straw or chopped corn stover is placed on the bottom of the compost area. The base layer should be at least two-feet thick for larger animals, cows, and swine greater than 200 pounds, and one-foot thick for poultry and swine less than 200 pounds. The base allows airflow beneath the animal and absorbs liquids that are generated during decomposition.

Placing animals: Carcasses are placed in a single layer on top of the base and must be two feet from the sides of the pile. For small animals, such as chickens or piglets, there should be at least six inches between the animals. For larger hogs, the separation should be one foot or more. Do not stack animals directly on top of each other (see adding additional animals). For large animals, place the feet down to avoid exposure during composting.

Covering animals: A layer of damp* amendment two-feet thick is placed over the animals. The amendment may be up to 50% recycled compost. If using recycled compost, add one foot of the compost first, then add one foot of amendment. The cover helps to absorb odors and insulate the pile to retain heat. If the cover is too thin or dry, odors may be released, which may attract scavenging animal and be annoying to neighbors. For piles without a roof, the amendment should be mounded so that it sheds rainwater.

*A handful of amendment should feel like a damp sponge.

Adding additional animals:  Create a hole in the cover amendment, making sure to maintain a layer of four-six inches above the animals already in the pile and keeping a buffer of two-feet from the sides of the pile. Place a new layer of animals in the pile, with spacing of six inches between small animals and one foot between larger animals. Cover the new animals with 2 feet of damp amendment. Layers of additional animals and amendment can be added to the pile until it is five feet high or, if using a bin, it is full.

Measuring temperature: he temperature of the pile is the best way to monitor the microbial activity during composting. It should be measured at several locations near where the animals are in the pile. The goal is to reach at least 131°F for at least 3 days to reduce pathogens, insects, and weed seed germination. Record the temperature to document the composting process. For example, decreasing temperature may indicate moisture or mixing is needed. Note that piles started in cold weather may not start composting immediately.

Mixing the pile: When the temperature is less than 110oF for one week, mix the pile. Lift or turn to mix materials. A handful of compost materials should feel like a damp sponge.  If the material is too dry, mix in water. If it is too wet, mix in dry amendment. If bones are exposed on the surface after mixing, cover them with amendment. After mixing, the pile will reheat. When the pile has reached its required number of composting days in the primary bin or windrow and the temperature is less than 110°F, mix the pile and move it to the secondary bin or pile.

Storage: Once the secondary pile has reached the recommended number of days for stage 2 and the temperature falls below 110°F, move the entire pile to storage for at least 30 days. The compost is done when the temperature is stable (no longer increasing or decreasing) and the material is dark and crumbly, with little odor. If bones are not easily crushed, return them to a new pile. Finished compost can be used as 50% of the cover amendment for a new pile. The compost may also be used on the farm where it was produced. It should be tested for nutrient content and land applied at acceptable agronomic rates.

Record keeping: Record the dates when the pile is built, mixed, and moved. Also, record the dates additional animals are placed in the pile, which is needed to determine the earliest date the pile can be mixed. The number of animals, pile temperature, and any observations should also be recorded to document the process and determine when the pile should be mixed or moved.

Leachate: There should be no liquids leaking from the pile. If present, this leachate can lead to water contamination and generate odors. If moisture is visible, cover it with sawdust. For new piles, increase the depth of the amendment in the base to reduce the risk.

Exposed animals: If bones or other parts of the animal are showing, they should be covered with 1 foot of damp amendment as soon as possible. Exposed animal parts are unsightly and may attract pests, such as rodents, birds, and flies that could spread disease.

REMINDER: Before composting can be used to dispose of dead animals, the Ohio Animal Mortality Certification Course must be completed.