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:
- Front-end loader for moving materials and carcasses, and for turning compost piles.
- 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.
- 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
2. Wika Instrument Corporation USA
Phone: (888) WIKA-USA
3. Tel-Tru Manufacturing Company
Phone: (585) 232-1440
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.