Composting Animal Mortalities

Despite the best intentions and care in animal agricultural facilities there are occasional animal mortalities.
Composting Animal Mortalities - Articles

Despite the best intentions and care in animal agricultural facilities there are occasional animal mortalities. Until recently there was a viable rendering industry that would collect the deceased animal and recycle the carcass back into useful products. Changes in economics and the emergence of disease agents that must be prevented from circulating in animal herds and flocks (e.g., transmissible spongiform encephalopathies, TSE) have made rendering of carcasses much less attractive or even impossible at times. Incineration at extremely high temperatures, long term storage in sealed land-fills, or alkaline digestion are the only proven technology that can destroy TSE's. Currently there is an operational incinerator at the Animal Diagnostic Laboratory at Penn State. The incinerator at the Pennsylvania State Veterinary Laboratory (PVL) in Harrisburg is provisionally approved to operate and PVL has provisional approval to operate an alkaline digestor as well. An alkaline digestor is at New Bolton Center, University of Pennsylvania.

Certainly for limited numbers of animals where carcass destruction is essential, (e.g., scrapie, chronic wasting disease, or bovine spongiform encephalopathy), high temperature incineration or alkaline digestion would be the preferred method of carcass disposal. Burial is permitted by regulation in Pennsylvania as an alternative for carcass disposal for routine animal mortalities. For limited numbers and in certain circumstances this form of disposal is acceptable. However, both incineration and burial have considerable limitations. Burial locations are restricted based on environmental concerns for ground water, limitations for numbers and mass, and season of the year. Incineration or alkaline digestion is also very limited by animal numbers, plus the carcasses must be transported to a fixed facility, and finally such disposal comes at a higher cost. Composting on site has proven to be a very cost effective means of carcass disposal. With some proper precautions composting can be an effective method of safely containing and disposing of animal carcasses.

Numerous extension and lay publications (Glanville 2003, Looper 2002) have described proper techniques for composting of large animals. Composting has been demonstrated as an effective, environmentally sound, and relatively easy method of recycling a carcass. Compost sampled after complete and stable fermentation can be free of pathogenic bacteria and viruses. There is considerable information on the fate of common pathogens in other forms of compost. In these types of substrates a relatively uniform composition is achieved and there is a high level of contact between the substrate and the pathogen. Temperatures and pH shifts can be accurately and consistently reached. Many plant pathogens are destroyed at temperatures >35° C and essentially all vegetative forms of animal pathogens are destroyed at temperatures above 55° C.

Large animals have been composted in a variety of substrates from bedded pack manure, leaves, straw, sawdust, shavings, and municipal yard waste. Typically a ratio of 25 to 30 parts of carbon substrate to 1 part protein, with a moisture content approximately 60% is ideal. In nearly all cases surrounding a carcass with a substrate like wood shavings, sawdust (can be from green wood), wood chips, or corn silage will achieve satisfactory composting temperatures and conditions. Since composting is an aerobic process (oxygen is required), pore size and enough space for air to pass between the particles into the pile is necessary.

A compost pile can be made by finding a level firm plot of well-drained soil at least 200 feet (some references list 300 feet) from any water source. The base should consist of a layer of carbon substrate (e.g., sawdust) at least 2 feet deep and extend 1½ to 2 feet beyond the width of the carcass. The carcass should be placed in the center of the base layer and buried completely to a depth of 2 feet around the entire carcass. For a single adult cow this represents a pile about 7 to 8 feet wide, 8 to 10 feet long and 5 to 7 feet high. Worksheets are available to help calculate the amount of carbon substrate needed for size and number of animals.

Often piles are left alone for up to 6 months. Additional substrate can be added on top if needed. If properly constructed, odor, pathogens, ground water, flies, and disturbance by dogs or other scavengers will not be a problem. Turing the pile adds oxygen and speeds up the process. Turning large piles as often as every 6 weeks would allow them to break down faster without risk of pathogen release into the environment. Properly-composted large animal carcasses will be completely broken down except for a very few parts of the largest, most dense bones in a minimum of 10 months. After 12 months even the densest bones can be crushed easily.

A concern that has emerged in the last few years is the question of chemicals entering the ground water near livestock facilities. One issue that has not been fully resolved is the fate of euthanasia solution in animal mortalities. A large animal might have 30 to 40 grams of pentobarbital in the carcass. This chemical is quite water soluble and might persist in the ground following burial for some time. One safe and environmentally friendly way of reducing agricultural chemicals is bioremediation. Bio-remediation is the use of cells or live organisms to remove, clean up, or break down a chemically-contaminated site or environment. Composting serves as a means of bioremediation. In limited preliminary work, data indicate that composting greatly reduces or eliminates euthanasia chemicals and most antibiotics. This is an added ecological advantage of using composting for animal mortalities.

In conclusion, while incineration, burial or tissue digestion are viable options for carcass disposal these methods have significant limitations and cost. In most cases animal mortalities can be safely and conveniently disposed of by composting. Composting, if done following simple but important guidelines, can be environmentally sound, economical, and safely eliminate pathogens and chemicals.

  • Glanville, T., et. al., Draft Guidelines for Emergency Composting of Cattle Mortalities, Iowa Agriculture and Home Economics Experiment Station, Iowa State University Extension, 2003.
  • Looper, M., Whole Animal Composting, New Mexico Cooperative Extension Service, Guide D-108, 2002

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Authors

David R. Wolfgang, VMD, MPH DABVP-Dairy