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Mortality Composting

Composting Livestock Mortalities Factsheet

Composting is a method to manage livestock mortalities (including mass mortalities resulting from avian influenza), butcher wastes and road killed animals. Read on or visit our factsheet to learn more.

Given the high costs and decreasing capacity of landfills and rendering facilities, on-farm composting offers a safe, financially viable, and sustainable management method for routine livestock mortalities. Composting optimizes natural decomposition to efficiently break down nitrogen-rich animal tissues, reduce pathogens, control odors, prevent scavengers, and more. However, compared to other organic residuals (e.g., landscape debris, food scraps), composting livestock mortalities requires special considerations and carefully followed best management practices.

 

Regulations 

Composting livestock mortalities may be subject to regulatory oversight depending on farm size (e.g., CAFOs), the number or total weight of mortalities per year, whether the mortalities occurred on- or off-site, and more. See Title 6 of the New York Codes, Rules and Regulations Part 361-3.2 and Environmental Conservation Law General Permit GP-0-22-001 for more details. 

 

Site Selection 

The site should be relatively flat (1-4% grade), well drained, and at  least 200' from residents, businesses, potable water wells, surface waters (e.g., lakes, streams), and state-regulated wetlands. Nearby trees can help capture any odors released during compost pile construction or turning, as well as provide operational privacy.

 

Carbon-rich Materials 

Prior to composting, stockpile a large supply of carbon-rich materials: coarse wood chips (1-6” particle size) for the base, and wood chips, wood shavings, leaves, chopped straw, old silage, bedding, and/or dry manure for the core and cap. Carbon materials balance the carbon-to-nitrogen ratio, create structure and porosity, facilitate airflow, absorb liquids, contain odors, deter scavengers, and insulate the pile's interior. 1 cubic yard of carbon-rich feedstock is needed for every 100-200 lbs of livestock mortalities. Source wood chips from local municipalities, utilities, lumber mills, or tree services.  

 

Compost Pile Construction

  1. Prepare a 2'-deep base of coarse wood chips (1-6” particle size) to absorb liquids and draw air into the bottom of the pile. (Do not drive equipment on the base.)

  2. Lance the animal’s abdomen (and rumen if applicable) to prevent bloating and the explosive release of gases, which could produce odors and uncover the carcass.

  3. Lay the carcass(es) on the wood chip base. Spread small animals (e.g., poultry, fish) evenly in a single layer without any separation. Medium- to large-sized animals should be separated by a few inches. Maintain a minimum buffer of 2' from the carcasses to the edges of the wood chip base.

  4. A second layer of animals <150 lbs each (e.g., poultry, sheep) can be added with 1-2' of carbon material between layers. Animals >150 lbs each (e.g., cows, horses) should be composted in a single layer.

  5. Cap the pile with a 2'-deep layer of various carbon materials to contain odors and insulate the pile.

     

Passive Aeration 

The compost pile should be >4’ high to provide adequate insulation and have a triangular or parabolic shape. As microbial activity increases and the pile's internal temperature heats up, cool air is drawn into the wood chip base and warm air will vent out the top. This upward draft (i.e., convection) replenishes oxygen for the microorganisms and prevents anaerobic conditions and odors. 

 

Moisture 

The optimal moisture content for composting is 50-60%. Livestock mortalities release significant moisture as they break down, but additional water may need to be added during pile construction or turning if the carbon materials are too dry. Feedstocks should have a slightly damp appearance. Excessively dry materials slow decomposition and excessively wet materials can become anaerobic and generate odors.   

 

Temperature 

To effectively reduce pathogens, the compost pile interior must reach >131°F (55°C) for multiple days or weeks, depending on the composting method (e.g., aerated-static pile, turned-windrow). These elevated temperatures are generated by microbial respiration as organic residuals are consumed. Use a long compost thermometer (36” stem length) to monitor temperatures throughout the process, at multiple points and depths (i.e., 18” and 36”) around the pile. 

 

Turning 

Turning reestablishes pile structure and airflow, rotates materials into the hot interior, and ensures more efficient and uniform decomposition. However, turning too soon can release intense odors, attract scavengers, and cause ammonia volatilization. For small animal mortalities (e.g., poultry, fish), wait at least 2-3 weeks until the first turning. For medium-sized animals (e.g., pigs, sheep, calves), wait at least 3 months. For large animals (e.g., cows, horses), wait at least 6-9 months. Piles may need to be recovered with ~6” of fresh carbon materials to contain odors after turning.

 

Curing & Screening 

When turning no longer results in temperatures >105°F, the active phase of the composting process is complete. Allow the material to stabilize and mature (i.e., “cure”) for 1-3 months. Large bones (e.g., skull, pelvis) and wood chips will remain at the end of the composting process and can be separated using a 1/2”-1/4” screener. Use these “overs” for the base of the next compost pile but not for the cap.

 

Testing 

Collect a 1-2 quart composite sample of finished compost derived from 1-2 pint subsamples taken from at least 5 spots around the pile and from 3 depths at each spot. Ship the sample to a laboratory for analysis, which will provide information about the compost's quality. If concerns exist about possible reportable or exotic diseases (e.g., avian influenza, prions), contact the appropriate state/federal authorities.

 

End Uses 

Composts produced from livestock mortalities tend to have more nutrients than those derived from other organic residuals (e.g., landscape trimmings) and can be applied to fields growing feed and fiber crops if time and temperature requirements were met and the product is sufficiently cured (CAFOs must ad-here to their Comprehensive Nutrient Management Plan). Overall, compost is a valuable soil amendment that can enhance soil health and crop growth.

 

Additional Resources: 

From the Cornell Waste Management Institute archives:

 

Horse Mortalities

Natural Rendering: Composting Livestock Mortality & Butcher Waste

 

Avian Influenza and Poultry Composting