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On-Farm Composting of Large Animal Mortalities

On-Farm Composting of Large Animal Mortalities

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Caitlin Price, Ph.D. Crop Science, Dept. of Crop and Soil Sciences, Lynne Carpenter-Boggs, Associate Professor, Dept. of Crop and Soil Sciences
Composting can be a safe and effective method for disposing of on-farm mortalities when the correct procedures are followed and the system is managed well. This bulletin provides the necessary information for large animal producers in Washington State to start and maintain a safe and effective on-farm mortality composting system.
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With proper management and materials, on-farm composting is an economical and environmentally sound method of routine or catastrophic mortality disposal. Compost­ing allows for immediate, year-round carcass disposal with minimal costs and equipment. Composting also protects surface and ground­water, reduces pathogens, and keeps valuable nutrients on the farm.

Composting is a biological process: aerobic microorganisms (bacteria and fungi) convert raw organic waste into stable, nutrient-rich organic matter. In large numbers, these microorganisms produce enough meta­bolic heat to increase temperatures inside the compost pile and kill pathogenic bac­teria and viruses. The basic requirements are organic raw materials (manure, straw, sawdust, etc.), a dedicated area, and careful management.

This bulletin contains the basic information needed to start a successful on-farm mortality composting operation for large animals. The same principles also apply to smaller animals (poultry, swine, etc.), but the time and materi­als required will be less.


State requirements for permitting and re­porting on-farm mortality composting vary depending on the size of operation and use of the final product. Most on-farm composting operations will be exempt from permitting, but check first! Contact the Washington State Department of Ecology or Department of Ag­riculture for more information. Department of Ecology guidelines for on-farm mortality composting are available online.


The basic tools needed for on-farm compost­ing of mortalities are:

  1. Front-end loader for moving materials and carcasses, and for turning compost piles.
  2. Logbook to record amount and type of compost materials, carcass weights, in­ternal pile temperatures, dates that piles are built and turned, and other important observations.
  3. Probe-type thermometer with a three-foot stainless steel stem to monitor internal pile temperatures.

Sources for Compost Temperature Probes

A thermometer is the most important tool for monitoring compost piles, and can be either a digital or dial type. The following companies manufacture thermometers that are designed for use in compost piles. We provide this information for your convenience and are not endorsing any company or manufacturer.

1. REOTEMP Instrument Corporation
Phone: (800) 648-7737
Web: www.reotemp.com

2. Wika Instrument Corporation USA
Phone: (888) WIKA-USA
Web: www.wika.com

3. Tel-Tru Manufacturing Company
Phone: (585) 232-1440
Web: www.teltru.com

Compost Materials

Compost materials can include many organic wastes commonly found on a farm. Attributes and values for some common compost mate­rials are listed in Table 1. Whatever materials are used, they should be blended or evenly layered to provide the best overall condi­tions and nutrient balance for the pile. Ap­proximately ten to twelve cubic yards of raw material is needed to compost a full-size cow. When choosing materials, it is important to consider nutrient content, moisture content, and structure.

The most important nutrient factor to man­age in raw compost materials is the ratio of carbon (C) to nitrogen (N), as both elements are essential for the growth of microorganisms. This ratio is called the Carbon-to-Nitrogen (C:N) ratio.

The ideal C:N ratio for compost materi­als is in the range of 30:1 to 40:1. Materials that are too high in nitrogen (low C:N) will give off ammonia and methane gases and/ or nutrient-rich leachate. Gases and leachate both are significant sources of odor. Materi­als that are very low in nitrogen (high C:N) will slow the composting process by limiting microbial growth. Carcasses are very dense and high in nitrogen and moisture. Therefore, high-carbon, absorbent materials to surround the carcass are necessary to balance essential nutrients and provide the right environment for microbial growth. Finished compost is low in available nutrients for further composting, but is useful as a ‘bio-filter’ when layered over a new pile to reduce odors and insulate in cold weather.



Copyright 2008 Washington State University

WSU Extension bulletins contain material written and produced for public distribution. Alternate formats of our educational materials are available upon request for persons with disabilities. Please contact Washington State University Extension for more information

Issued by Washington State University Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, sex, religion, age, color, creed, and national or ethnic origin; physical, mental, or sensory disability; marital status or sexual orientation; and status as a Vietnam-era or disabled veteran. Evidence of noncompliance may be reported through your local WSU Extension office. Trade names have been used to simplify information; no endorsement is intended.