Why Compost?

skid loader dumping load


Although mortalities from modern poultry and livestock production operations comprise a small percentage of the total number of animals raised, management of mortalities is an important task for modern livestock producers. Prompt and careful disposal of mortalities reduces the potential for disease transmission, air and water pollution, and attraction of insects and scavenging animals.

Rendering, incineration, and burial have long been used in the swine industry. Following the lead of the poultry industry, where composting has been used successfully for more than a decade, swine producers are now looking at composting as a flexible and low cost method for for swine mortality disposal. Why are swine producers attracted to composting? Perhaps the most compelling reason is illustrated by the photo of the skidloader and manure spreader shown above. Using equipment and management skills commonly applied in most livestock production operations, composting turns mortalities into a biologically stable, heat-treated soil amendment that can be applied to cropland with little risk of air or water pollution. Equally important, composting allows producers to manage mortalities promptly as they occur with no waiting for rendering service pickup, or for the ground to dry up or thaw out so that burial can be accomplished.

On-farm composting of mortalities got its start in the late 1980s after research at the University of Maryland showed that broiler chickens could be fully biodegraded in as few as 30 days. Since that time, composting has been rapidly adopted by the U.S. poultry industry. In their 1996 report, Agricultural Composting in the United States: Trends and Driving Forces, Kashmanian and Rynk (Journal of Soil and Water Conservation, May/June 1996) reported that about 5000 farms in the top 25 poultry-producing states were composting their mortalities. Faced with increasing concerns regarding air and water quality, biosecurity, rising fuel prices, and reduced access to rendering services, many other sectors of the animal production industry are now adopting composting.

Like rendering, incineration, and burial, composting has its “plusses and minuses,” but here are a few reasons that swine producers have given for considering composting.

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Reduced access to rendering service & increasing rendering fees

For many years, livestock producers throughout Iowa were served by numerous local rendering companies that recycled poultry and animal mortalities into valuable animal feed and similar products. Unfortunately, Iowa’s once extensive rendering service industry has shrunk dramatically in the past 20 years from 26 plants in 1983, to only 7 in 1996. As a result, some areas of the state can no longer get rendering service. In areas where service is available, increased haul distances and rising fuel costs have forced rendering service fees to increase.

rendering plants chart

One farm in central Iowa reports rendering costs of nearly $3,000 per year (for 2 visits/week). Despite the increased costs, rendering service still provides good value for the money, particularly for producers who want to minimize the amount of time and labor they spend on animal mortality disposal. Of greater concern than the rendering fees for many, however, is reduced frequency of service. During warm weather, twice weekly pickup often isn’t adequate. Biosecurity concerns associated with storing carcasses between redering service visits, and the possiblity of disease transmission as rendering trucks move from farm-to-farm, are additional reasons cited by some producers for switching to on-farm disposal methods.


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Air and water quality

Few industries have gotten more attention from regulatory agencies and environmental groups in recent years than livestock production. Air and water pollution are “hot” public issues that most producers strive to avoid if possible. Air and water regulations are becoming more stringent, however, and both burial and incineration have raised environmental concerns in the past. Over the years, many reports have cited concerns associated with incineration. Although a sound technology, and certainly one of the safest in terms of pathogen distruction, incinerators must be consistently operated at high temperatures to avoid odor-causing combustion by-products. Failure to preheat, and intermittent overloading, are two causes of odorous emissions. While avoidable, it takes only one serious odor incident to upset neighbors and passersby, so constant vigilance is needed to avoid such problems.

Research has shown that animal mortalities placed in lightly-loaded burial sites located in well-drained soils may decay in as few as two years. If burial sites are heavily loaded or located in poorly-drained soils, however, decay can take a decade or longer, and shallow groundwater can be impacted by high concentrations of ammonia-nitrogen, chloride, and biochemical oxygen demand. Responding to the potential for groundwater pollution, many U.S. states and Canadian provinces now regulate on-farm burial including such things as:

  • number of animals buried per acre;
  • minimum burial depth; soil drainage class;
  • minimum depth to groundwater; and
  • minimum separation distances from wells and streams.

Iowa Department of Natural Resources (IDNR) guidelines limit on-farm burial to 44 butcher or breeding hogs, 7 slaughter or feeding cattle, 73 sheep or lambs, or 400 poultry carcasses on any given acre per year. For further information on IDNR animal disposal rules, see the IDNR factsheet entitled Frequently Asked Questions – Dead Animal Disposal (revised 2013) and Chapter 100.4(2) Special requirements for farm waste, farm buildings, and dead animals of the Iowa Administrative Code.

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Timeliness & producer control

For many operations, animal mortality disposal is a daily task that must be handled promptly to minimize odors, problems with insects or scavenging animals, and the risk of disease transmission. Whatever the disposal
option, it’s essential that it function smoothly and reliably under all weather conditions. Ideally, the disposal system should be flexible to handle day-to-day variability in animal mortality. Composting has been shown to meet these requirements as well, if not better, than most other options. A properly designed composting operation will operate effectively in summer or winter, has sufficient capacity to handle normal daily variations in loss rate, and places the producer in complete control of the disposal operation.

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Department of Agricultural & Biosystems Engineering, Iowa State University