Draft Guidelines for Emergency Composting of Cattle Mortalities

Clell V. Bagley, D.V.M., USU Extension Veterinarian

Emergencies Happen ... Be Prepared!

Fires, floods, building ventilation failures, and catastrophic disease …..such disasters don't happen often, but when they do livestock producers suddenly can be faced with livestock deaths and carcass disposal problems.

These draft emergency composting guidelines are based on preliminary findings of an on-going 3-year study at Iowa State University that was begun in 2002 at the request of the Iowa Department of Natural Resources (IDNR). The guidelines may be modified as additional findings become available, but are being published now in draft form to provide Iowa's cattle industry with the up-to-date recommendations on composting practices that:

Are suitable for large animal carcasses;
Can be implemented quickly using equipment and materials available on the farm;
Have acceptable impacts on soil, water, and air quality; and
Prevent the spread of disease.

For detailed information on methods and results of the cattle composting study, visit the project website.

Why Consider Composting?

Iowa's cattle industry is facing new and difficult animal disposal issues that cannot be addressed solely through rendering or on-farm burial.

In the event of agro-terrorism or a naturally-occurring disease outbreak local rendering capacity could be temporarily overwhelmed, as was the case in Great Britain during the foot-and-mouth epidemic in 2001.
With consolidation of the rendering industry, haul distances have increased, making transportation more expensive and potentially in short supply in the event of a widespread livestock disease emergency.
During an outbreak of a highly contagious livestock disease, off-farm disposal of diseased carcasses could increase the risks of disease transmission.
USDA rules (implemented in January, 2004) that prohibit marketing of non-ambulatory cattle will increase the number of animals that must be disposed of through rendering or on-farm disposal.
Burying many large animals requires high-capacity earthmoving equipment not found on most farms, and during at least 25% of the year frozen soils make burial in Iowa very difficult.
Recent IDNR analyses of geographic data indicate that shallow groundwater, exposed bedrock, or other environmentally sensitive situations make large-scale burial undesirable in about 40% of Iowa.

Although composting is unlikely to replace rendering or burial for emergency disposal of cattle, it is a flexible disposal option that can help to overcome the problems outlined above. Specifically:

Composting facilitates rapid on-farm containment of carcass odor and pathogens, and elevated temperatures produced during composting help to destroy pathogens;
Most dairy and beef cattle farms have the equipment and materials necessary for composting;
Unlike burial, frozen soils and seasonal high water tables do not seriously impede composting; and
Carcass composting followed by land application of the compost poses less pollution risk to shallow groundwater than burial.

Disease vs Non-Disease Emergencies

Disposing of cattle that have a transmissible disease calls for extra precautions during composting. If infectious disease is the cause of death, the following composting procedures can help to reduce the risks of pathogen survival and disease transmission.

To achieve high composting temperatures that are capable of killing pathogens as quickly as possible, cover carcasses with silage, or a 6-12 inch layer of moist manure capped with ground straw or ground cornstalks.
To minimize the risk of releasing pathogens into the wind, do NOT turn the pile during carcass decomposition.

NOTE: Due to many unknown factors regarding the biodegradability of the prions that cause bovine spongiform encephalopathy (commonly called BSE or mad cow disease), composting should NOT be used for disposal of cattle suspected to have BSE.

For livestock deaths not caused by disease, less stringent composting procedures can be used.

Ground cornstalks, ground hay, or similar dry porous materials that do not produce high heat quickly may be used to cover the carcasses.
Turning of the compost pile is permissible (although not necessarily required) after a minimum of 60-90 days.
Excavation and spreading of the compost on corn or soybean ground can be done as soon as soft tissues and internal organs are fully decayed and only skeletal remains are present (typically 8 - 12 months after composting is begun).

Compost Disposal

Preliminary results of field biosecurity tests using two common avian vaccine viruses suggest that composting windrows constructed with the recommended depths of cover material can retain and inactivate viruses within 3-4 weeks during cold weather, and in a matter of days during warm weather. Nevertheless, if cattle death was caused by a potentially contagious disease, skeletal remains and cover material should not be excavated until advised to do so by animal health officials. If the safety of the finished compost cannot be ascertained by sampling and testing, skeletal remains and cover materials can be incinerated, buried, or rendered to further reduce disease risks.

Skeletal remains and cover materials for non-diseased cattle can be spread on corn or soybean ground using a dry manure spreader. At the present time, spreading on grazing land, or on land used to produce human or animal food crops that will be consumed without further processing, is not recommended. Skeletal remains (bones) are normally clean and dry, but the bones of mature cattle can be quite thick and may not totally decompose for several years. Turning bones under the soil with a moldboard plow is advisable if the disposal area is located near to non-farm residences frequented by pets or children. Disking has not been a successful method for covering large bones.

The nutrient content of finished cattle mortality compost can be highly variable and is heavily dependent on the carcass loading rate and amount and type of cover material used. Limited sampling of cattle mortality compost has shown total N content in finished compost of roughly 0.6-0.7% (wet weight basis) where silage and ground cornstalks have been used as cover material. Total P2O5 content for the same composts was in the 0.4-0.5% range (wet weight basis).

These materials are abstracted from a study at Iowa State University and provide some of the latest information on composting of adult cattle. For the full information visit the website.