Farming Magazine - September, 2013

FEATURES

Mortality Composting

By Katie Navarra


In New York and Pennsylvania, a deadstock composting site must be located at least 200 feet from any water source, sinkholes or areas that have excess water.
Photos courtesy of Cornell Waste Management Institute, Department of Crop and Soil Sciences.

Farms that raise livestock are faced with the mortality and, ultimately, the disposal of their animals. State regulations dictate how deadstock can be disposed of, but methods can include burial, incineration, rendering and/or composting.

Each state's department of agriculture or environmental protection agency can provide details. For example, Pennsylvania regulations require that deadstock be disposed of in 48 hours. These animals can be buried, incinerated, composted or rendered.

In New York, "Burying is still allowable, but can be difficult because of the weather or geography," explained Jean Bonhotal, compost specialist with the Cornell Waste Management Institute, Department of Crop and Soil Sciences.

A number of farms have traditionally relied on a rendering service to pick up a carcass and dispose of it off-site. Hiring a renderer can be costly and can include limitations on materials accepted, especially in regard to butcher waste. Rendering fees are on the rise as the market value of animal hides, tallow and meat/bonemeal decreases.

Farms are increasingly choosing to compost their animal carcasses on-site. Mortality composting is a sustainable and relatively simple alternative. Animals of any size, from poultry and swine to cattle and equine, can be composted using materials and equipment readily available on most farms.

Preparing a carcass for composting can be done at any time during the year, even during winter months. Not only does mortality composting offer a lower-cost option for disposing of animal carcasses, it also provides better sanitation than burying an animal in soil. Heat generated during the composting process kills pathogens that could become a potential biosecurity threat.

"We were asked to go to Brazil to teach mortality composting because they don't have a winter kill and they needed a way to reduce pathogens in the soil," Bonhotal said.



The carcass should be covered with composting material, which might include wood chips, old silage, sawdust, dry stall bedding and semisolid manure. Compost specialist Jean Bonhotal advises the use of chunky materials for better air circulation, which helps in the composting process.

Composting at your farm

Composting is the microbial breakdown of organic matter to a more stable material and requires a proper carbon-to-nitrogen ratio. To achieve the proper ratio, Bonhotal said that animal spacing is key. "You are placing the animal in a carbon envelope, and air needs to get in to keep the microorganisms working," she explained.

Before composting any animal, check local and state regulations, and then design the composting site according to the regulations. Make sure the site is an appropriate size for the farm.

The University of Kentucky College of Agriculture offers a guide called "On-Farm Composting of Animal Mortalities" (http://www2.ca.uky.edu/agc/pubs/id/id166/id166.pdf), by Stephen F. Higgins, Sarah J. Wightman and Amanda A. Gumbert. The paper suggests that the size of a composting facility should be based "on the estimated weight of average daily mortalities. Weights of animals typically found on the farm can be calculated based on farm production records or industry standards. ... Use these weights plus mortality rates associated with age groups to calculate the weight of average daily mortalities."

Composting sites can be as simple as using windrow formations, or you can construct bins with concrete sides and a roof. The size of the farm and state regulations will help determine what is needed.

The guide also suggests: "For small operations with unroofed facilities without sides, follow the standard criteria for sizing based on total operation size: operations with up to 100 head, use a 60-by-32-foot composting pad; operations that have between 100 and 200 head, use an 80-by-32-foot composting pad; and operations that have between 200 and 300 head, use a 110-by-32-foot composting pad."

Preparing a composting site

As stated earlier, check with your state department of agriculture and/or environmental protection agency for details specific to your state. The methods described below are approved in New York and Pennsylvania.

  • Choose a location that is at least 200 feet from any water source, sinkholes or areas that have excess water.
  • Spread organic material 2 feet deep. The material should include larger pieces (4 to 6 inches long).
  • Cover the carcass with composting material such as old silage, sawdust or dry stall bedding. Using some semisolid manure will speed up the process. "Wood chips work the best, but manure, haylage and silage can all be used. Chunky materials work best because the air circulates better," Bonhotal explained.
  • Use at least 2 feet of composting material for younger animals.
  • Leave for four to six months.
  • Remove any large bones before spreading compost on fields.

A word of caution: Animals that exhibited signs of neurological disease or those that died under quarantine should not be composted. Report the information to the appropriate authorities and dispose of the carcass according to their recommendations.

Composting does not require much ongoing maintenance, but it does need active management. The composting material should maintain a temperature between 140 and 160 degrees Fahrenheit and moisture content between 40 and 60 percent. Ideally, the carbon-to-nitrogen ratio will be 30-to-1, but a range between 20-to-1 and 40-to-1 is acceptable.

What's left behind?

Large bones will remain once the composting process is complete and can be used as a portion of the base material for the next carcass composted. The composted material may also be applied to soil as fertilizer and incorporated into the farm's nutrient management plan.

Bones will be left in the pile, but should be brittle. If a rear-tine manure spreader is used for land application of the compost, the bones should shatter. Some sifting may be needed.

Studies have been conducted to determine what, if any, types of medications are still present in the soil after composting is finished. "We looked at barbiturates used in euthanasia drugs, and those are breaking down in composting," Bonhotal noted. "Wormer [ivermectin] is breaking down pretty well in the environment," she added. However, hormones do persist; they don't break down during composting. Antibiotics have not yet been studied.

Additional information, including instructional videos and tip sheets, are available from the Cornell Waste Management Institute free of charge. Visit http://cwmi.css.cornell.edu for details.

Penn State Extension also has information available at http://extension.psu.edu/animals/composting/composting-process-1/mortality-composting-guidelines.

Katie Navarra is a freelance contributor based in Clifton Park, N.Y., and writes about agriculture and the equine industry regularly.