A review of methods and microbial risks associated with composting of animal carcasses in the United States

Authors: BERGE, ANNA CATHARINA - WASHINGTON STATE UNIV; GLANVILLE, THOMAS - IOWA STATE UNIV; Millner, Patricia; KLINGBORG, DONALD - UNIV OF CALIFORNIA

Submitted to: Journal of the American Veterinary Medical Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2008
Publication Date: 1/1/2009
Citation: Berge, A.B., Glanville, T.D., Millner, P.D., Klingborg, D.J. 2009. A review of methods and microbial risks associated with composting of animal carcasses in the United States. Journal of the American Veterinary Medical Association. 234:47-56.

Interpretive Summary: Most livestock and poultry production operations result in few mortalities, particularly with young animals or birds. In cases of epidemics or adverse weather, large numbers of mortalities may occur within a short period of time. Whatever the cause or extent, all mortalities must be managed to reduce pathogens and their spread, to protect the environment, and to reduce negative aesthetic impacts. Typical options for dealing with carcasses have included: Rendering, Composting, Incineration, Landfilling, and Burial (in soil or pits). The latter three options are increasingly limited. Furthermore, in situations involving catastrophic mortalities, existing rendering capacity may be exceeded. For these reasons, carcass composting, when properly conducted, has been used in many places in the U.S. to successfully manage on-farm animal mortalities. Carcass composting differs from composting manure and green waste because carcasses are typically composted whole and piles are not turned until self-heating has subsided. The overall strategies for constructing and managing carcass compost piles are described in this report. Based on extensive published results from livestock and poultry carcass composting studies, it is clear that proper composting eliminates most pathogens and reduces the number of spore-forming bacteria, prions, and viruses. The disinfection capacity of carcass composting helps protect public health and the environment by substantially reducing the pathogen load in material that is ultimately land applied. This is an important element in reducing the source of food and water contamination. Soil contaminated with pathogenic bacteria from improperly managed mortalities may contaminate water sources or runoff from pastureland. A risk assessment approach which includes all stages of disposal of animal mortality, such as handling, transportation, processing, storage and disposal, would provide a useful perspective for decision-makers who want to compare composting with other means of mortality management. The information in this report will help inform livestock and poultry producers, scientists, regulators, and others interested in evaluating the use of carcass composting as an animal mortality management and carcass/bedding disinfection tool.

Technical Abstract: Animal carcass composting for both routine and emergency management of food animal mortalities is an alternative method of carcass disposal in those situations where conventional methods are inadequate. Carcass composting has been referred to as ‘above ground burial in a bio-filter with pathogen kill by high temperature.’ In most composting systems a carbon to nitrogen ratio of 25:1 to 30:1, moisture content of 50-60 percent and a temperature in the range 43-65°C are considered optimal for supporting the performance of the microorganisms that drive the composting process. Carcass composting differs from composting other materials such as manure and green waste and present some unique challenges. Carcasses are typically composted whole and do not present uniformly chopped substrate for microbial action, nor are these compost piles turned as frequently. Both of these factors contribute to a non-uniform compost composition at the end of the process. While allowances for this non-uniformity need to be made in the criteria, it has been demonstrated that well designed carcass compost systems with proper maintenance and monitoring do result in a safe and efficient method of disposing of animal mortalities with minimal environmental impacts. Studies demonstrate proper composting eliminates most pathogens and reduces spore-forming bacteria, prions and other selected pathogen levels. Additional studies are needed to determine the fate of spore-forming bacteria and prion agents in carcass composting. Regulatory agencies are encouraged to evaluate carcass composting by using a risk assessment approach which includes all stages of disposal of animal mortality, such as handling, transportation, processing, storage and disposal. Risk comparisons need to account for the sum of risks from the point of death to sequestration or destruction of potential animal mortality threats associated in the various disposal systems under consideration.