When animals die or are slaughtered on farms, carcasses and parts that are unfit for use as food should be disposed of properly. Safe and environmentally responsible disposal of animal carcasses, whether an individual death or during significant mortality events, is an essential consideration.
Information on the safe and lawful disposal of carcasses can be obtained from local environmental protection agencies. Because state and federal regulations regarding the science of disposal of animal carcasses and biohazard waste is constantly changing, this discussion only addresses carcass disposal and not associated biohazard wastes such as bandaging materials. When the circumstances under which death has occurred suggest a transmissible disease or toxic hazard, the nearest animal health official should be notified immediately.
As general precautions, persons handling carcasses and disinfectants should wear protective clothing and be properly equipped to complete the tasks of disposition and disinfection. Premises should be promptly cleaned in a manner that prevents any infectious or toxic health hazard to domestic or wild animals or people.
The method of disposal should preclude contamination of soil, air, and water. Hides and other parts of animals that have succumbed to infectious diseases or toxins should be safely disposed of and not retained for use.
There are restrictions on carcass disposal for cattle ≥30 months old because of specified risk materials (tissues in which prions that cause bovine spongiform encephalopathy [BSE] concentrate). Sheep or cattle diagnosed with or suspected of being affected by scrapie or BSE, respectively, must not be rendered. The preferred means of disposal for these animals is incineration, although they may also be buried (see below).
Ordinarily, rendering is a safe, rapid, and economic method of disposal of carcasses. Renderers are required to use equipment and methods that prevent health hazards. Local regulations specify requirements for transportation of carcasses to rendering plants. During transportation, biosecurity must be considered to avoid spreading infectious agents into the environment.
When a site acceptable to the local environmental protection agency is available, burial is usually the preferred method of disposal. In selecting a burial site, it is necessary to consider the adequacy of soil depth and to avoid underground electrical cables, water pipes, gas pipes, septic tanks, and water wells. The prevention of secondary toxicosis or exposure to infectious agents must be considered (eg, the burial of a carcass infected with blastomycosis could potentially contaminate the soil and groundwater, putting scavengers at risk).
The burial pit or trench should be at least 2.3 m wide and 3 m deep (7 × 9 ft). The pit is a cave-in hazard and must not be entered without proper shoring, and any other appropriate precautions should be taken. At this depth, 1.3 m2 (15 ft2) of floor space will accommodate a mature bovine or equine carcass, 5 mature pigs or sheep, 100 mature chickens, or 40 mature turkeys. For each additional meter (3 ft) in depth, the number of animals per 1.3 m2 of floor space may be doubled. Contaminated litter, soil, manure, feed, milk, or other material should be placed in the pit with the carcasses and covered with at least 2 m (6 ft) of soil. The covering soil should not be compacted. Decomposition and gas formation cause cracking, bubbling, and leaking of fluids from a compacted burial site. The soil should be mounded and neatly graded.
Certain landfills are licensed to accept animal carcasses. Check with the landfill in your area. If this is allowed, all biosecurity practices should be followed during transportation.
Burning in an incinerator that is operated in compliance with local laws and ordinances is an excellent means to dispose of one or a few carcasses and is the preferred means for sheep with scrapie and cattle with BSE.
Burning carcasses in an open site should be done only when legally permitted. Burning poultry carcasses should be considered only when burial is not feasible. The burn site should be away from public view and on flat, open ground that is clear of buildings, hay or straw stacks, overhead cables, and shallow underground pipes or cables. Locations upwind from houses, farm buildings, roads, or populated areas, and those from which precipitation runoff may contaminate the environment, should be avoided.
Carcasses must be placed on a quantity of combustible supporting materials sufficient to reduce them completely to ashes. The material must also be arranged in a manner to permit an adequate flow of air to the fire. Gasoline or other highly volatile combustible liquids should not be used.
To prepare the fire bed, an area of ground should be staked out to accommodate the number of carcasses to be burned: 8 × 3 ft for each mature cow or horse, 5 mature pigs or sheep, 100 mature chickens, or 40 mature turkeys. The fire bed burns best if at a right angle to the prevailing wind.
Under favorable conditions, burning should be complete in 48 hours. Additional combustible material should be added as needed. When the fire has died out, the ashes should be buried and the area cleaned, graded or plowed, and prepared for seeding.
Developed for use on poultry farms, composting has been successfully used for swine, cattle, horse, sheep, and goat carcasses. The proper balance of material (oxygen, moisture, nitrogen, and carbon) is required for this natural degradation process to reach a temperature of 130°-150°F, which is sufficient to kill most disease-causing organisms, allowing the end product to be suitable for use as a soil amendment. However, toxins and any medications or drugs in the animal at the time of death will not necessarily be degraded through this process. Care should be taken to protect the compost from excessive rain and to secure it from predators.
Tissue digestion, fermentation, and dry extrusion methods have been developed to process certain dead animals and animal waste, destroy pathogenic organisms, reduce volume, and produce feedstuffs. Tissue digestion, both alkaline and thermal degradation, may be available in animal diagnostic laboratories. Local environmental protection agencies and state agriculture departments should be consulted concerning the acceptability of these and other possible alternative disposal methods.
Removal and safe disposal of manure, feed, and debris by burial or burning, followed by thorough scraping and cleaning of all buildings and equipment, must precede the application of chemical disinfectant. Except for steam cleaning, cleaning with aqueous solutions is practical only at temperatures above freezing. A cleaning agent such as trisodium phosphate or sodium carbonate dissolved in hot water will facilitate cleaning. All traces of the cleaning agent must be rinsed away with clear water before disinfectant is applied because some may inactivate the disinfectant. Provision must be made to contain and safely dispose of cleaning solutions, rinse water, and disinfectant.
Disinfectants recommended for general use on surfaces free of organic matter are sodium or calcium hypochlorite (1,200 ppm available chlorine), iodine, phenol, and quaternary ammonium compounds. Newer disinfectants use a combination of products (eg, quaternary ammonia and glutaraldehyde) to enhance efficacy. The selection of the best disinfectant for a particular situation, as well as the contact time and concentration required for the concerning pathogen, is complex and beyond the scope of this discussion. The CDC has an excellent overview in their disinfection and sterilization guidelines. In addition, information on disinfectants for specific animal disease agents can be obtained from state or federal animal health agencies. Disinfectants should bear the approval statement of the EPA in the USA or of a similar agency in other countries. Label instructions for application must be followed.