Published December, 2009

Proper livestock stewardship does not cease when an animal dies. Despite sound management, all horse producers will experience losses due to weather, disease, or other natural causes. Options for carcass disposal are dwindling due to enhanced regulation and decreased availability of rendering services. To address growing environmental and biosecurity concerns, many producers are investigating composting as a viable alternative to more costly options of mortality disposal. Considering the abundance of stockpiled muck, used bedding, and feedstuffs available on many horse farms, composting represents a feasible and effective method of dealing with fallen stock.

Composting is a simple, low-cost disposal method that is environmentally sound and yields a versatile product. The finished material can also be stockpiled and reused to help compost other mortalities. Composting takes advantage of the natural decomposition process conducted by microorganisms and can be controlled under managed conditions. This process reduces the size of carcass material by removing organic products, water, and energy in the form of carbon dioxide, vapor, and heat. In addition, many pathogens are destroyed by the high temperatures and beneficial bacteria generated during the decomposition process, yielding this method of disposal as an approved alternative, according to Kentucky's Office of the State Veterinarian.

Some producers may be hesitant to adopt this practice on their own farms because they may not have the time or equipment required. However, when done correctly, mortality composting requires minimal labor input and can take advantage of equipment already present on most horse farms. University of Kentucky trials have successfully demonstrated that horse mortalities can be reduced to a few large brittle bones in as little as six weeks. A properly managed pile will not create odors, attract scavengers, or lead to spread of disease.

This brief composting introduction was written as a guide for on-farm composting of horse mortalities and can assist in designing and troubleshooting composting systems.

Composting Equipment and Materials

Co-composting materials

A bulking agent will be needed to cover and insulate the carcass, wick up excess moisture that is released, and balance the carbon-to-nitrogen ratio (C:N). Horse carcasses usually contain a high concentration of nitrogen and water, so bulking agents high in carbon aid in keeping the C:N ratio at the desired range of 25:1 to 40:1.

Horse composting systems may utilize a variety of bulking agents as co-composting materials. A combination of fine and coarsely textured materials will work best to promote optimal conditions within the pile. Examples of bulking agents include sawdust, straw, muck, old bedding, wood chips, reused compost, and yard waste, just to name a few.

The use of finished or stable compost as an outer layer will help abate odor and gas release, maintain microbial activity, and prevent scavenger access. Finished compost also serves as a biofilter, which contains beneficial bacteria that will jump-start the composting process.

Equipment

Two pieces of equipment are necessary to manage composting facilities. A front-end loader is needed to place carcasses in the pile, transport co-composting materials, and turn or move the pile contents. A temperature probe is desirable to monitor internal pile temperatures. A long-stemmed agricultural thermometer works great and is recommended for any mortality compost facility. Additionally, a compost log or notebook for recordkeeping might be necessary to document the temperature and record conditions during the composting process.

Site Selection

Choosing an appropriate site is the first step in successful mortality composting. Site selection, preparation, and runoff abatement are crucial for mortality composting facilities. When selecting a site consideration should be given to a number of factors, including water and soil quality protection; biosecurity; neighbor complaint and nuisance prevention; and minimization of operation and management challenges. Selected sites should be accessible in all weather conditions. Composting facilities should not be built in flood plains or within 300 feet of a water well, stream, sinkhole, pond, property line, or public road.

Constructing a Windrow Pile

Once a proper site is located, and the permit is acquired, it is time to begin the compost pile ("windrow"). All runoff needs to be collected and treated though an appropriate vegetated buffer or plumbed to an established waste storage facility. A requirement of the Kentucky Division of Water is that the site can collect and detain runoff from a 24-hour, 25-year storm. Moisture is one of the limiting factors in the composting process. The top of the pile should be sloped or mounded to allow rainwater to shed. Care needs to be taken to divert runoff, ensure proper insulation during the composting process, and prevent excess moisture from permeating the pile.

A compacted layer of impervious materials, such as a stack pad or heavy traffic pad with geotextile fabric, should be constructed to minimize liquid infiltration into groundwater supplies and aid in pile turning. Size considerations for stack pad construction should be based on the amount of material to be composted, which can be calculated using the average mortality rates for individual farms.

After securing an impervious surface you will need to create a base. The base should consist of a 2- 3-foot-thick layer of bulking agent large enough to cover the entire surface. Horse carcasses should be placed in a single layer, centered on the base material, and they should not be placed within 8-12 inches of the edges of the compost pile.

Once you have centered the carcass on the pile, you will need to cover it with a 3 to 4 foot thick layer of bulking agent. Using sawdust or finished compost here will minimize odors, provide protection against scavengers, and maintain proper moisture and temperature conditions within the pile. Moisture can be determined by squeezing compost in your hand. If moisture drips from your hand, the pile is too wet after squeezing the compost. If your palm does not get wet, the pile is too dry. Optimum moisture is when the hand is wet. It is imperative that all parts of the carcass are completely covered to ensure proper decomposition and to prevent scavenger attraction to the pile.

The Composting Process

As previously mentioned, use a thermometer to accurately monitor internal pile temperatures and to ensure that optimal temperatures are being reached. Temperatures will increase within two to four days of loading carcasses in the pile with ideal temperatures ranging between 130° F to 160°F during active decomposition.

Once temperatures begin to decline, or a few months have passed, you may turn or move the pile with a front-end loader without the threat of releasing pathogenic bacteria. Turning helps aerate the pile, establish a more homogeneous mixture of materials, speeds up the overall composting process, and creates room to accommodate other mortalities.

Once the pile has been turned, continue to monitor temperatures, as they may increase again with further decomposition. When significant heating does not occur after turning, then the product is finished and ready to be stockpiled for future composting of mortalities or land-applied as a soil amendment. Compost should be tested for pathogen and nutrient content before land applying. If the material is to be land-applied, it should be applied to crop fields as a fertilizer source using the Natural Resource Conservation Service Standard for Nutrient Management.

Rules and Regulations

In order to legally compost mortalities, a permit is required, which is issued by the Office of the State Veterinarian. The cost of the permit is $25 and is renewed every five years. The permit application requires the name and address of the compost owner, location and description of the composting facility, and the composting procedure. All animal composting facilities are subject to inspection by the State Veterinarian or his or her representative. Any animal carcasses not composted should be disposed of in a manner consistent with KRS 257.160 (see ID-167, On-Farm Disposal of Animal Mortalities).

Kentucky law requires that reasonable and cost-effective efforts shall be taken to prevent odor, insects, and pests. Odors can be controlled by maintaining proper moisture, aeration, and carbon-to-nitrogen ratio during the composting process. To control pests and prevent transport of contagious diseases, all carcasses shall be inaccessible to scavengers, livestock, and poultry. Limiting odors, insects, and pests, and access of scavengers and other animals requires proper supervision and monitoring during the composting process.

Steve Higgins is the director of environmental compliance for the University of Kentucky Agricultural Experiment Station. Emily Bruner is an agricultural extension assistant.