Mortality composting helps farmers

posted on September 18, 2013 11:25am

Taking care of animal mortality is an unavoidable respon-sibility on livestock farms. Whether mortalities are due to natural causes, accident or disease, each one must be disposed of in an environmentally appropriate and biosecure way. As off-farm options for dealing with animal mortalities dwindle, more farms are turning to on-farm composting and are learning to turn the compost into a valuable product.

“During the 2013 Michigan Ag Expo, we talked about finishing the compost process,” Dale Rozeboom, Michigan State University (MSU) Extension specialist and MSU animal science professor. “We also discussed compost characteristics, quality, fertility and saleability.”

MSU Extension research and education in on-farm mortality com-posting helps farmers ensure that mortality management is conducted in a safe and effective way that protects the environment. Following MSU Extension guidelines helps farms comply with the Michigan Bodies of Dead Animal Act (BODA). Compliance is required for verification through the Michigan Agriculture Environmental Assurance Program (MAEAP).

BODA rules state: “Finished compost has no visible pieces of soft tissue and that the bones remaining at the time of final utilization shall be fully decomposed, or easily crumbled during the mechanical spreading process, or gathered and placed in a new batch of compost feedstock for further decomposition.” Complete breakdown of bones is not always possible with animals that were six months or older at death and have undergone just six months of composting. On most farms, separation of bones from what would otherwise be finished mortality compost is a manual and undesirable job. Also undesirable, and a violation of BODA, is when mortality compost is spread on the fields leaving whole bones on the surface. They may become a neighborhood nuisance if displaced by pets and wildlife.

Composting is a dynamic process. The animal carcass is enclosed in a mixture of plant or fiber-rich materials such as wood chips, waste feed or used compost. Microorganisms in the mixture will utilize moisture, carbon and oxygen to break down the carcass tissues while releasing heat. Farm operators who use mortality composting ultimately discover that the larger bones of an animal carcass can take a considerable amount of time to be completely reduced. For older animals, significant decompo-sition of the bones may take one to two years.

How to deal with residual bones from livestock composting was discussed at a series of daily demonstrations hosted by MSU Extension during the 2013 Michigan Ag Expo:

• Conditions in which bones can be field applied or buried.

• Screening bones from the finished compost and reincorporation into compost.

• Mechanical screening and grinding.

More information on dealing with residual bones from livestock composting can be found at by searching for “screening compost”. Several helpful mortality composting guides are also availabe at the MSU Extension Bookstore online at