When animals die or are slaughtered on farms, carcasses, tissues, body parts, and by-products that are unfit for use as food, including those from animals that have succumbed to infectious diseases or toxins, should be disposed of promptly (typically within 36–48 hours, as determined by the individual state) and properly.
Responsible disposal of animal carcasses, whether from individual deaths or from major mortality events, should maximize protection of public health and inactivation of pathogens, and minimize biosecurity risk and environmental impact.
Other considerations pertaining to the selection of carcass disposal method include feasibility/availability and regulatory restrictions, speed of implementation, public acceptance, and cost-effectiveness.
Information on the safe and lawful disposal of carcasses can be obtained from state and local environmental protection, agricultural, animal health, and public health agencies. Appropriate state and local regulatory agencies should always be consulted regarding permits for the chosen disposal method and site.
Because state and federal regulations regarding the science of disposal of animal carcasses and biohazard waste is constantly changing, this discussion addresses the disposal of only carcasses, tissues, body parts, and by-products and not associated biohazard wastes, such as contaminated supplies.
Disposal of wildlife carcasses may be subject to regulations under the Endangered Species Act, which should be consulted for those species; however, that is beyond the scope of this discussion.
The method of carcass disposal should preclude contamination of soil, air, or water and should protect the carcass from access by insects and scavengers, which may transmit disease.
In instances of potentially infected carcasses or mass depopulation and disposal due to a disaster or emergency event that affects animals, state and federal animal health officials may require specific disposal methods that may affect indemnity payments, if applicable.
There are restrictions on carcass disposal for cattle ≥ 30 months old because of specified risk materials—ie, tissues in which prions that cause bovine spongiform encephalopathy Bovine Spongiform Encephalopathy (BSE) reside. Sheep or cattle diagnosed with or suspected of being affected by scrapie Scrapie or BSE, respectively, must not be rendered. The preferred means of disposal for these animals is incineration; however, they may also be buried (see below).
As a general precaution, persons handling carcasses and disinfectants should wear protective clothing and be properly equipped to complete the tasks of disposal, cleaning, and disinfection.
After the carcass is removed from the premises, the site should be promptly cleaned in a manner that prevents any infectious or toxic health hazard to domestic or wild animals or humans, and it should be disinfected to destroy or inactivate the pathogen of concern.
Rendering of Animal Carcasses
Ordinarily, rendering is a safe, rapid, and economic method of carcass disposal. Rendering is closely regulated for product quality and environmental compliance. Local regulations specify requirements for transporting carcasses to rendering plants (eg, whether a permit is needed); typically, rendering companies offer a pickup service. Most plants can accept whole carcasses (ie, including hides or feathers, if necessary).
Renderers are required to use equipment and methods that prevent health hazards. The rendering process involves reducing the carcass to small pieces, cooking it, separating its components of protein, fat and waste, and distributing those components accordingly; dried protein is used to make pet food and fats may be used for biodiesel. The heat treatment of the rendering process inactivates most biological contaminants; however, biosecurity measures must be taken during carcass handling and transportation to avoid the transmission of infectious agents into the environment.
Animals euthanized by means of a chemical form of euthanasia, including barbiturate overdose, are not allowed to be accepted at rendering facilities, because the rendered product will test positive for the drug.
In any premises where rendering is used, all animals rendered must retain their heads. Pentobarbital-euthanized animals must be permanently marked on the head (preferably with a large “P” applied with fluorescent orange all-weather paint stick) to identify them as animals that should not be rendered.
Sheep or cattle diagnosed with or suspected of being affected by scrapie or BSE, respectively, must not be rendered, because the rendering process does not inactivate prions.
Burial of Animal Carcasses
When a site acceptable to the state or local environmental protection agency is available and accessible (eg, not frozen), burial may be used for carcass disposal. Selection of a burial site should take into account the following considerations:
adequacy of soil depth, to avoid underground electrical cables, water pipes, gas pipes, septic tanks, and water wells
prevention of secondary toxicosis or exposure to infectious agents through soil or groundwater contamination, to protect other domestic and wild animals, including scavengers
possible prohibition against or specific requirements (eg, minimum depth) in some areas for burial of animals euthanized with barbiturates
Adequate land must be available for burial, and specific metrics for determining the land area or excavation volume necessary for the burial of different species and sizes of animals are readily available from local or state agricultural and environmental agencies.
Appropriate safety precautions should be taken when digging and adding carcasses to the burial pit or trench. Carcasses should be punctured or vented before burial, and they should be buried along with any potentially contaminated or infectious material (eg, litter or bedding, soil, feces, feed, milk).
Carcasses should be covered with the excavated earth, according to appropriate procedures to facilitate rainwater runoff and minimize soil erosion and compaction, and the site should be monitored regularly.
Incineration of Animal Carcasses
Burning or cremating in an incinerator that is operated in compliance with local laws and ordinances is an excellent means of disposal of one or a few carcasses because it is effective at destroying infectious agents, including scrapie and BSE. Incineration on-site is a biosecure option in instances of disease outbreak.
Purchasing, maintaining, and fueling commercial incinerators can be expensive, and incinerator operators may be required to obtain a permit from the state or local environmental agency. Incineration, particularly open-air burning, can result in air quality problems that pose a public health risk, and should be done only when legally permitted by local and state animal health, environmental, and fire agencies.
Adequate land must be available for open-air incineration, and specific metrics for determining the land area necessary for incineration of different species and sizes of animals are available from local or state regulatory agencies.
Care should be taken in appropriate selection of the burn site and timing with respect to public view and access; distance from structures on, above, or below the ground; and weather, wind direction, and flow of runoff.
Open-air burning must include appropriate quantities of combustible supporting materials and have sufficient airflow to reduce carcasses completely to ashes. It may also be necessary to burn potentially contaminated or infectious material (litter or bedding, feed, etc) without highly volatile combustible liquids (eg, gasoline).
When the fire has died out, the ashes should be buried and the area cleaned, graded or plowed, and prepared for seeding.
Composting of Animal Carcasses
Composting has been successfully used for swine, cattle, horse, sheep, and goat carcasses. Composting is environmentally friendly and poses minimal risk to human health, and when done properly, composting is effective at inactivating pathogens.
On-site composting is a biosecure option that may be done in bins (see bin composting photograph Topical Therapies for Keratomycosis ) or windrows (see static pile composting photograph Topical Therapies for Keratomycosis ).
The proper balance of materials (oxygen, moisture, nitrogen, and carbon), as well as appropriate temperature and pH, is essential to effective composting of carcasses. Temperatures of ~55°C–65°C (130°F-150°F) are sufficient to kill most disease-causing organisms, making the end product suitable for use as a soil amendment. However, toxins and any medications or drugs in the animal at the time of death may not be degraded through this process.
Care should be taken to protect the compost from excessive rain and to secure it from predators.
Other Disposal Methods for Animal Carcasses
Some landfills are licensed to accept animal carcasses. State and local regulations may require special licenses to transport dead animals to a landfill. If disposal in a sanitary landfill is allowed, careful biosecurity practices should be followed during transportation.
Tissue digestion, fermentation, and dry extrusion methods have been developed to process certain dead animals and animal waste, destroy pathogenic organisms, decrease volume, and produce fertilizer, feedstuffs, or further refined products such as biogas or biodiesel. These methods are safe and environmentally friendly; however, start-up and maintenance costs are relatively high, and the methods are appropriate for processing only small numbers of carcasses at a time.
Tissue digestion, by both alkaline and thermal degradation, may be available in animal diagnostic laboratories. Other carcass disposal technologies under research and development include gasification, thermal depolymerization, dehydration, and use of plasma technology. State and local environmental protection agencies and agriculture departments should be consulted concerning the acceptability of these and other possible alternative disposal methods.
See the table for a concise comparison of carcass disposal strategies.
Cleaning and Disinfection of Premises After Animal Carcass Disposal
Dry cleaning to remove gross contamination and organic material (eg, feces, feed, bedding) from the premises, equipment, and other contaminated facilities or surfaces should be performed promptly after carcass disposal to mitigate the potential transmission of infectious disease.
After dry cleaning, the premises and associated items should be washed with a detergent solution to further remove organic matter, rinsed, and when possible, dried completely before disinfectant is applied. A variety of disinfectants are available; use of an EPA-registered (or equivalent in countries outside the US) disinfectant labeled with a claim to remove any pathogens of concern must follow manufacturer directions for concentration and contact time. Additional information and recommendations are available from state and federal public health and animal health agencies.
A variety of factors affect the efficacy of cleaning and disinfection, including surface type, pH, water quality, temperature, and weather, so it is important to select a disinfectant that will be efficacious under the given conditions. The premises and items may then be rinsed thoroughly and allowed to dry.
Multiple methods for carcass disposal are available.
The number and size of carcasses, available land, protection of public health, pathogen inactivation, and minimization of biosecurity risk and environmental impact should all be considered in determining the best method for each situation.