The primary objective of disposal of carcasses, animal products, materials and wastes is to prevent the dissemination of infection. This process is therefore part of an emergency animal disease eradication programme, particularly when a stamping-out policy is followed. It is important from an aesthetic point of view. Disposal should be completed as soon as possible after destruction, to minimize opportunities for infectious material to disperse. Carcasses are much easier to handle before decomposition has set in.
This manual outlines disposal methods appropriate for the emergency animal diseases most readily transmitted by fomites-foot-and-mouth disease, Newcastle disease, African swine fever and avian influenza - and zoonotic diseases. Less rigorous disposal methods may be appropriate for less readily transmitted diseases and non-zoonotic diseases. Carcasses and other items awaiting disposal should be guarded to prevent unauthorized access and to prevent domestic pets, wild animals and birds from removing potentially infectious material. Control of insects should be considered if there is a risk of passive transmission by insects to nearby susceptible species. If disposal is delayed, carcasses should be thoroughly sprayed with an approved disinfectant.
Disposal of carcasses
The basic requirements of disposal: simple equipment and human resources.
Organizing stamping out
Among the activities is verification of numbers and ownership of animals. This may involve whole communities and is necessary to streamline the compensation process.
Before disposal work starts, personnel should be fully briefed. The nature of the disease and any hygiene requirements associated with zoonotic diseases should be explained on site.
Respirators should be supplied to personnel when there is any risk to humans from the organism involved or if large amounts of dust are generated.
It is crucial to select a site which is well-protected from people and scavenging animals. On some occasions it may be necessary to mount a guard at the site for the first few days.
Depending on local circumstances, burial may be the preferred method of disposal because it is quicker, cheaper, environmentally cleaner and easier to organize because there are fewer outside resources required (see Burial, p. 35).
General factors to be considered are:
Disposal of animal carcasses and other infectious material may involve some adverse environmental consequences. It is important for the environmental aspects of proposed disposal activities to be properly considered, with advice from environmental agencies where possible, so as to ensure that the impact of such consequences be minimized. Consultation with relevant authorities, e.g. environmental protection agencies, will be necessary to obtain specific information on a number of these factors.
Where burial, cremation or rendering are not considered practical or difficult to carry out on the infected or dangerous-contact premises, consideration could be given to transferral of carcasses and/or infectious material to another site for disposal by burial, cremation or rendering. This may be necessary when considering the disposal of materials from laboratories and in situations where site limitations, such as available space or watertable, effectively prevent on-site disposal. Furthermore, in some circumstances, such as with large volumes of material from feedlots, it may be preferable to dispose of carcasses by rendering if suitable facilities are available locally or can be transported to the site.
If infectious and dangerous-contact premises are adjacent or in close proximity, a common disposal site may be used.
Disposal of carcasses
Trucks are an essential and quick means of moving carcasses to the disposal sites.
Transport should be in a leak-proof container, such as a large skip, covered with tough polyethylene covers and sealed at the top. It should not be overloaded - half a metre or more (depending on distance to be travelled and temperature) should be left clear for expansion of carcasses. Carcasses should not be slashed before loading. Vehicles should travel slowly to avoid splashing of contaminated material. Staff should carry a supply of an approved disinfectant and basic equipment to deal with minor spills during a journey. All vehicles must be cleaned and disinfected before leaving the premises and after unloading.
Important considerations for selecting burial sites include:
The preferred equipment for digging burial pits is an excavator, which is the most efficient for the construction of long, deep pits with vertical sides. Advantages include the ability to store topsoil separate from subsoil. The equipment can be used to fill the pit with carcasses or other materials and close it without disturbing the carcasses.
Loaders, bulldozers, road graders and backhoes - or manual labour for small jobs - may be used if excavators are unavailable. With the exception of backhoes, all other equipment requires continual movement of the machine over the site while the pit is being dug. Excavators and backhoes remain in a fixed position, so they move soil faster, with less cost and less damage to the area around the pit. Most excavators have an attachable hammer for excavating rock.
Burial pit construction
The dimensions of the burial pit will depend on the equipment used, site considerations and the volume of material to be buried. Pits should be as deep as possible, with vertical sides; reach of machinery, soil type and watertable level are the usual constraints. The pit should of a width such that the equipment can fill it evenly with the material to be buried. If a bulldozer is used, for example, the pit should be no more than one blade width, about 3 metres, because it may be difficult to push carcasses in from one side and fill the pit evenly. The aim should be to avoid having to move carcasses once they are in the pit. The length of the pit will be determined by the volume of material to be buried.
In deciding the dimensions of the pit, consideration needs to be given to the method of filling the pit with carcasses or other material. Carcasses will generally be unloaded from tipper trucks or pushed into the pit by a loader or bulldozer from one of the long sides. Excavators may be used to fill pits with carcasses placed close by; this is useful if soil stability does not permit trucks or other heavy equipment to operate close to the pit edge.
Disposal of carcasses after a mass epidemic
Even if an epidemic clears an animal population, it will be necessary to dispose of carcasses by the proper means.
Using heavy earthmoving equipment
Heavy earthmoving equipment is essential for digging disposal pits and moving carcasses.
The following guidelines may be of assistance in determining the pit volume required. The base of the pit must be at least 1 m above the watertable. Allow a fill capacity of about 1.5 m3 for each adult beast or 5 adult sheep. At least 2 m depth of soil is required to cover carcasses to ground level. For example, a pit 3 m wide and 5 m deep filled with carcasses to within 2.5 m of ground level will accommodate 5 adult cattle per linear metre (3 × 2.5 × 1 = 7.5 m3; 7.5/1.5 = 5 cattle or 25 sheep).
When closing the pit, surplus soil should be heaped over it as overfill. The weight of soil prevents carcasses from rising out of the pit because of gas entrapment, prevents scavengers digging up carcasses, helps filter out odours and assists in absorbing the fluids of decomposition. After pit subsidence, it will be necessary to replace any topsoil not utilized during pit closure.
Disposal of carcasses by burial; (A) open pit, (B) freshly closed pit.
Poultry to be destroyed will normally be in a container such as a skip or body of a truck and the dimensions of these containers should be used as a guide to the volume of the pit required.
Gas production. Gas produced by decomposition within unopened carcasses may result in considerable expansion of the buried material, to the extent that the surface of the closed pit may rise and carcasses may be expelled. It is recommended that large animal carcasses be opened by slashing the rumen (cattle) or the caeca (horses) to permit escape of gas. There appears to be little benefit in opening small animal carcasses. If carcasses are to be opened, it should be done at the side of the pit. Under no circumstances should personnel enter the pit during filling.
Covering buried carcasses with lime
Covering the carcasses with lime is a requirement, since it protects the carcasses from being uncovered by carnivores and earthworms.
Lime should be added to pits, to prevent earthworms from bringing contaminated material to the surface after pit closure. Cover the carcasses with soil, 400 mm is suggested, and add an unbroken layer of slaked lime - Ca (OH)2 - before filling is completed.
Lime should not be placed directly on carcasses, because in wet conditions it slows and may prevent decomposition.
Site inspection. Inspection of the burial site after closure is recommended so that appropriate action can be taken in the event of seepage or other problems. The objective is that the site should return to its original condition. Before restocking is permitted, the burial site should be inspected again to ensure that there is no possible biological or physical danger to stock. This would normally be several months after pit closure.
Safety considerations. Safety of personnel is an overriding consideration. Aspects to consider include: hygiene of personnel working on the site, availability of rescue equipment if a person falls into the pit or if the pit wall collapses and protection against dust. Operations should be controlled by the site supervisor/team leader; staff must be briefed before operations begin.
Cremation should be considered only when burial is not possible. In countries where earthmoving equipment may not be available for deep burial, where putrefaction is not a deterrent and/or poverty dictates that eating habits should not be fastidious, cremation is preferred. Available methods include funeral pyres, incinerators and pit burning.
The principle is to place carcasses on top of sufficient combustible material, making sure that the arrangement of fuel and carcasses allows adequate air flow to enter the pyre from below, so as to achieve the hottest fire and the most complete combustion in the shortest time.
Important considerations are:
Preparation of firebed
The fireline should be sited at right angles to the direction of the prevailing wind to maximize ventilation. Space for air can be provided by digging trenches under the pyre and/or elevating the firebed. Fuel supplies should be stacked upwind and the fire built from that side; carcasses should be loaded from the opposite side. The width of the firebed is governed by the size of carcasses to be burnt; for adult cattle allow 2.5 m. To determine the length, allow 1 m per adult beast.
If the firebed is to be built on the ground, dig trenches of 30 × 30 cm to act as air vents. These should lie in the direction of the prevailing wind at 1 m intervals under the length of the proposed firebed. If the firebed is to be elevating, lay rows of baled straw and heavy timbers parallel to the prevailing wind and then another layer of timbers crossing the bottom layer, leaving a gap of about 20 cm between timbers. Then lay other fuel, such as lighter timber or straw bales, over this timber support.
Burning is a common method of disposing of carcasses. It is discouraged because of the large amount of fuel it requires.
Stack carcasses across the firebed with larger carcasses on the bottom and smaller carcasses on top (Figure 18), preferably with the carcasses on their backs and alternating head to tail. Excavators or front-end loaders are best but lifting jibs, tractor forklifts or cranes and chains can be used. After carcasses have been placed on the firebed, the extensor tendons may be cut to prevent legs being extended during burning.
When the carcasses have been loaded and weather conditions suitable, saturate the firebed and carcasses with diesel or heating oil - do not use petrol - and prepare ignition points at 10 m intervals along the length of the firebed. These can be made of rags soaked in kerosene.
Remove all vehicles, personnel and other equipment well away from the firebed. Start the fire by walking into the wind and lighting the ignition points along the way.
Disposal of carcasses by cremation.
The fire must be attended at all times and be refuelled as necessary. Use a tractor with a front-mounted blade or a front-loader. Ensure that any carcasses or parts of carcasses that fall off the fire are put back on. A well constructed fire will burn all carcasses within 48 hours. The ashes should be buried and the site restored as fully as possible.
Local availability will govern the type and amount of fuels. The following can be used as a guide per adult beast:
Fuel requirements may be estimated on the basis that one adult cattle carcass is equivalent to four adult pigs or shorn sheep or three adult woolly sheep.
Biological incinerators are an efficient carcass-disposal system, achieving safe and complete disposal with minimal pollution. The cost of establishment and operation, however, and lack of portability mean that incinerators may not be readily available. Incinerators are usually only suited to disposal of small amounts of material. Special procedures must be followed for transportation of infected material from infected premises to the incinerators and disinfection of containers and vehicles.
Pit burning, also known as air-curtain incineration, is a technique for burning material in a pit, using fan-forced air. Pit burners are used by some local authorities to burn vegetable matter with a high moisture content. The equipment consists of a large capacity-fan, usually driven by a diesel engine, and ducts to deliver the air, which may be preheated, into the long side of a trench. The angle of the airflow creates a curtain of air that acts as a top for the incinerator and provides oxygen that induces high combustion temperatures. Hot air recirculates in the pit, achieving complete combustion. Additional fuel is required to initiate combustion; once the fire is burning, however, the fuel requirement is reduced. Pit burners would be suitable for continuous operation on a relatively small scale and have the advantage of being transportable. They appear to be especially suited to pigs and fat sheep.
In countries where mechanical equipment is difficult to obtain and the above methods appear sophisticated, a combination of burning and burial has been used successfully to dispose of pig carcasses and would be suitable for small ruminants and possibly small numbers of cattle as well. After the trench had been dug, it was lined with old motor tyres, on which the carcasses were placed. The carcasses were soaked with diesel and ignited with a small amount of petrol. Fires were watched until the carcasses were burnt and then the trench was covered over.
Rendering may be an option for the disposal of carcasses if suitable Oplants are available. Only rendering plants using a high-temperature batch-rendering process should be used. A satisfactory rendering process would involve grinding of the raw product, solvent extraction of lipids at about 100°C for one hour and high temperature (160°C) treatment of both carcass meal and tallow for at least a further 40 minutes.
The end product of rendering must pass relevant microbiological tests before release.
Considerable human resources are required for burial, even when equipment is available.
Where there is a minor risk of fomite spread, composting of stable manure, feeds, hay, litter and bedding is a possible alternative to burial or burning. Composting should be done in a secure area not accessible to susceptible animals.
All contaminated and potentially contaminated carcasses, animal products, materials and wastes should be disposed of by one of the methods outlined in Methods of disposal on p.35. Specific disposal considerations apply to the materials listed below.
The disposal of milk products presents particular difficulties, because large volumes are often involved. It is essential that milk should be treated to inactivate any virus before disposal (see Decontamination manual, Section 6). Following inactivation, disposal options must be considered. Milk held on-farm is usually in small quantities and can be disposed of in the burial pit. On properties where carcasses are cremated, milk should be disposed of in the effluent pit.
Where there are large volumes of contaminated milk at dairy factories or in tankers, the milk should always be inactivated and then pumped into a shallow, fenced pit, which must be covered over when the milk has evaporated or seeped into the surrounding soil.
Effluent from washing at dairy factories presents special problems because of the sheer volume. Chemical treatment of large volumes of effluent may render it unacceptable to a sewage disposal unit but 0.2 percent citric acid should cause no problems. The danger from effluent is greatly reduced by dilution; above-normal quantities of water freely used in the usual cleaning processes will further reduce the danger.
Where effluent is normally irrigated over pastures, they should not be grazed for two weeks after treatment. Rennet, casein, whey or other wastes must not be sprayed over pastures, discharged into drains or fed to animals, unless treated with disinfectant.
Before disposing of hatching eggs and hatchery waste in burial pits, all material should be macerated to ensure extinction of life. Assistance of the poultry industry should be sought for supply of suitable equipment and guidance on its use.
Small amounts of solid manure may be disposed of by burial or cremation. See Decontamination manual, Section 6.
If required, these byproducts should always be buried because they do not burn well.
Animal by-products: products of animal origin destined for industrial use, e.g. raw hides and skins, fur, wool, hair, feathers, hoofs, bones and fertilizer.
Animal products: meat products and products of animal origin, such as eggs and milk, for human consumption or for use in animal feeding.
Control area: a declared area in which defined conditions apply to all movements of specified animals or things to, from and within it. Conditions applying in a control area are less rigorous than those in a restricted area.
Dangerous-contact animal: an animal showing no clinical signs of disease but which, by reason of its probable exposure to disease, will be subjected to disease control measures.
Dangerous-contact premises: premises containing dangerous-contact animals.
Decontamination: includes all stages of cleaning and disinfection.
A cattle market is a risk enterprise during an epidemic, capable of spreading disease fast and over large distances.
Fomites: inanimate objects such as boots, clothing, equipment, vehicles, crates and packaging that can carry an exotic agent and spread disease through mechanical transmission.
Infected premises: a defined area, which may be all or part of a property, in which an infectious disease or disease agent exists or is believed to exist.
Premises: a defined area or structure, which may include all or part of a farm, enterprise or other private or public land, building or property.
Quarantine: legal restrictions limiting movement imposed on a place, animal, vehicle or other things.
Rendering: processing by heat to inactivate infective agents. Rendered material may be used in various products according to particular disease circumstances.
Restricted area: a declared area around an infected premises that is subject to intense surveillance and movement controls; smaller than a control area.
Risk enterprise: a livestock or livestock-related enterprise with a high potential for disease spread, e.g. an abattoir, milk factory, artificial breeding centre or livestock market.
Salvage: recovery of some market value by treatment and use of products, according to disease circumstances.
Stamping out: eradication procedures based on quarantine and slaughter of all infected animals and animals exposed to infection.
Susceptible animals: animals that can be infected with a disease.
Suspect animals: animals that may have been exposed to an exotic or serious infectious disease such that quarantine and intensive surveillance are warranted; or an animal not known to have been exposed to a disease agent but showing clinical signs requiring differential diagnosis.
Suspect premises: premises containing suspect animals.
Swill: leftover food such as kitchen and table scraps used to feed pigs.
Tracing: the process of locating animals, persons or things that may be implicated in the spread of disease, so that appropriate action can be taken.
Vector: a living organism, frequently an arthropod, that transmits an infectious agent from one host to another. A biological vector is one in which the infectious agent must develop or multiply before becoming infective to a recipient host. A mechanical vector is one that transmits an infectious agent from one host to another but is not essential to the life cycle of the agent.
Zoonosis: disease that can affect humans as well as animals.
Ford, W.B. 1994. Air-curtain IncineratorTM system test for disposal of large animal carcases. Foreign Animal Disease Report, 22(2). United States Department of Agriculture.
McDaniel, H.A. 1991. Environmental protection during animal disease eradication programmes. OIE Revue Scientifique et Technique, 10(3): 867–884.
Pryde, L.C. 1990. Slaughter and disposal of sheep. Agnote Reg, 3(15). Australia, NSW Agriculture.
First things first - slaughter and disposal of sheep, cattle and horses (video). Australian Animal Health Laboratory (AAHL), 1993. Available from AAHL, Geelong, Australia.
First things first - slaughter and disposal of pigs (video). AAHL, 1993. Available from AAHL.
First things first - slaughter and disposal of poultry (video). AAHL, 1993. Available from AAHL.