Mass euthanasia, or the humane killing of large numbers of farm animals, is at times required in an emergency animal disease outbreak to control and prevent further spread of the disease. An emergency animal disease is a disease that is either exotic to Australia, a variation of an endemic disease (disease that is already present in a population), a serious infectious disease of unknown cause, or a severe outbreak of an endemic disease that will have serious social or trade implications at a national level .
In an emergency animal disease outbreak in Australia, the response to that disease is coordinated by the relevant state or territory authority. It is critical in these events that animal welfare is a priority when determining the best course of action.
Why is mass euthanasia required?
- infected herds/flocks of animals with a disease, including diseases which cause significant illness/death, where the disease can spread to humans or the spread must be controlled by law
- herds/flocks nearby infected herds/flocks where it is too risky to await a disease outcome investigation
- pre-emptive control of other herds/flocks close to infected animals
- animal welfare reasons, such as where transport restrictions are in place or staff shortages at abattoirs causing on-farm overcrowding or feed shortages; and
- natural disasters.
The animal welfare concerns associated with mass euthanasia
Disruptions to the usual supply chain process such as transport restrictions during emergency animal diseases outbreaks, staffing shortages, and abattoir closures or shift reductions may result in less animals being able to be slaughtered than planned. This is a particular concern for intensively farmed species, such as pigs and poultry, who are at risks of experiencing overcrowding on farm due to limited indoor housing space, potential food shortages from reduced or no supply, and health problems. In these circumstances where animal movement on and off the property is often completely stopped or limited mass euthanasia has to occur on farm.
To ensure animal welfare is safeguarded during short, medium and long-term disruptions stakeholders in the supply chain must have coordinated contingency plans in place. Animal welfare must be one of the primary considerations in these contingency plans, including contingencies in the event that mass euthanasia is determined to be the only measure to prevent negative animal welfare outcomes. In situations where mass euthanasia is required, there are three critical points where animal welfare must be considered :
- Animal handling and restraint prior to killing
- The stunning/killing method used
- Confirmation of death
It is important that animals are handled as little as possible to avoid any unnecessary stress. Any euthanasia method that requires minimal handling of animals should always be considered when possible.
In the event of transport restrictions or limitations, animals being transported in trucks or trains should be offloaded and provided feed, water and shelter as soon as possible. Depending on the situation, animals may then be returned to their property/farm of origin or directed to a suitable holding yard or facility.
The euthanasia method chosen must consider all factors relating to the situation. On one farm, several different methods may be needed to euthanase animals of different sizes and ages. Whatever the method, it must ensure that animals are killed immediately and effectively while avoiding any potential pain and stress.
It is critical following any euthanasia method that all animals are checked to confirm they are dead before they are moved for appropriate disposal. At least three signs of death should be checked in each animal, these signs may include :
- No rhythmic respiratory movements
- No corneal reflex or ‘blink’
- Dilated pupils and/or glazing of the eyes
- No heartbeat or pulse
- Pale mucous membranes that do not refill after touching
- No withdrawal reflex/pain response (not a reliable sign)
- No jaw or tongue tone
- Onset of rigor mortis (occurs several hours after death)
Current methods of mass euthanasia used
When mass euthanasia is required, there are numerous factors that must be taken into consideration to determine what method is most appropriate for each specific situation. Some of these factors include [1, 4]:
- The animal species and age
- Number of animals
- Whether domesticated or wild animals
- The type of farming or housing system
- Available facilities and equipment
- Practicality and efficiency of the method
- Training required
- Human health and safety
- Handling and stress level on the animals
- Type of disease and sampling considerations
- Biosecurity and legal considerations
- Disposal and decontamination requirements
Considerations must also be made for the order in which animals are euthanased, which in most cases means that affected/infected animals will be euthanased first, then animals who have been in direct contact with suspect and infected animals, and then other susceptible or at-risk animals. In some cases, due to animal welfare considerations, certain animals must be given priority during euthanasia. Animals that require special welfare considerations may include animals that cannot access feed or water; sick and distressed animals; unweaned or young animals; animals in parturition (labour) or late pregnancy; as well as aggressive or potentially dangerous animals .
If on-farm mass euthanasia of poultry is required, consideration must be given to the type of production (breeder farm, hatchery, meat chicken farm or layer hen farm), the type of housing, and the size and age of the birds.
- Carbon dioxide gas (whole shed, partial shed or containerised) has been used in several types of poultry (e.g., meat chickens and layer hens), however, special consideration must be given for birds that may be more resistant to carbon dioxide gas such as young birds or water birds (ducks or geese).
- Foam (high expansion air or gas-filled) has been used for floor-based poultry housing systems and has demonstrated results comparable to carbon dioxide gas.
- Non-penetrating captive bolt guns may be more appropriate for a smaller number of birds or larger birds such as turkeys.
If on-farm mass euthanasia of pigs is required, consideration must first be given to whether the affected pigs are housed in indoor or outdoor production systems, and then to the different sizes and ages of pigs produced on the farm. Special consideration must be given to sows who are farrowing (in labour) or nursing, and sows with unweaned piglets should be euthanased together simultaneously.
- Carbon dioxide gas or inert gas (nitrogen) for unweaned piglets or piglets <5kgs.
- Non-penetrating captive bolt guns for piglets <5kgs.
- Penetrating captive bolt gun in pigs >5kgs.
- Firearms for pigs >5kgs in outdoor systems where pigs are unable to be caught or handled.
Following the method of euthanasia and once pigs are confirmed to be at least unconscious a secondary method of euthanasia, such as pithing (destroying the brain stem) or exsanguination (bleeding out), should always be done, especially in adult pigs, to ensure the pigs are effectively killed.
What is the RSPCA’s view on mass euthanasia methods?
RSPCA Australia is opposed to all inhumane methods of killing. Animals should either be killed instantly or rendered insensible until death ensues, without pain, suffering or distress.
 Animal Health Australia (2007) AUSVETPLAN operational manual – livestock welfare and management. Version 3.0.
 Berg C (2012) The need for monitoring farm animal welfare during mass killing for disease eradication purposes. Animal Welfare 21:357-361.
 AVMA (2019) AVMA guidelines for the depopulation of animals: 2019 edition. Version 2019.0.1.
 OIE (2019) Killing of animals for disease control purposes. Terrestrial Animal Health Code 1:7.6.
 Animal Health Australia (2015) AUSVETPLAN operational manual – destruction of animals. Version 3.2.
 Alphin R, Rankin M, Johnson K et al (2010) Comparison of water-based foam and inert-gas mass emergency depopulation methods. Avian Diseases 54:757-762.
 Benson E, Malone G, Alphin R et al (2007) Foam-based mass emergency depopulation of floor-reared meat-type poultry operations. Poultry Science 86:219-224.
 Jongman EC, Fisher AD (2021) Euthanasia of laying hens: An overview. Animal Production Science 61:1042-1047.
 Meyer R, Morrow M, Stikeleather L et al (2013) Evaluation of CO2 application requirements for on-farm mass depopulation of swine in a disease emergency. Agriculture 3:599-612.
 Dalla Costa FA, Gibson TJ, Oliveira SEO et al (2021) On-farm culling methods used for pigs. Animal Welfare 30(4):507-522.