«Training Euthanasia of Injured Wildlife Jim Pollock B.V.Sc Thousands of animals are euthanased every year in this country. After every option has ...»
Euthanasia of Injured Wildlife
Jim Pollock B.V.Sc
Thousands of animals are euthanased every year in this country. After every option has
been exhausted to find foster homes for domestic as well as native animals, there are
still thousands that must be humanely destroyed. This unpleasant but necessary task
requires a certain level of skill and knowledge if it is to be done humanely and
These notes are designed to give some theory and to provide the understanding necessary for humane animal euthanasia.
Introduction The term euthanasia is derived from the Greek word eu meaning good and thanatos meaning death. A “good death” would be one that occurs with minimal pain and distress.
It is our responsibility as veterinarians and human beings to ensure that if an animals’ life is to be taken, it is done with the highest degree of respect, and with an emphasis on making the death as painless and stress free as possible. Euthanasia should result in rapid loss of consciousness followed by cardiac and respiratory arrest and ultimate loss of brain function. In addition, the technique should minimise the distress and anxiety experienced by the animal prior to the loss of consciousness.
The criteria for painless death can only be established after mechanisms of pain are understood.
Pain is the sensation (perception) that results from nerve impulses reaching the cerebral cortex via ascending neural pathways. I will not go into depth in understanding pain but there are a few things to keep in mind. All drugs that relieve or suppress pain work best if given before pain is initiated. Once pain is caused it is much more difficult to control.
Discomfort, fear, anxiety and depression will all increase the stimulus of pain.
Remember that pain will have a reflex action on the cardiac and respiratory function as well as the pituitary and adrenal systems.
For pain to be experienced, the cerebral cortex and subcortical structures must be functional. If the cerebral cortex is non-functional because of hypoxia, depression by drugs, electric shock, or concussion, pain is not experienced. Therefore the choice of euthanasia agent or method is less critical if it is to be used on an animal that is anaesthetised or unconscious, provided that the animal does not regain consciousness prior to death.
Stress can be defined as the effect of physical, physiologic, or emotional factors (stressors) that induce an alteration in the animal’s homeostasis or adaptive state.
An animal’s response to stress depends on its experience, age, species, breed, and current physiologic and psychologic state.
As with many other procedures involving animals, some methods of euthanasia require physically handling the animal. The amount of control and kind of restraint will be determined by the animal species, breed, size, state of domestication, degree of taming, presence of painful injury or disease, degree of excitement and method of euthanasia.
Proper handling is vital to minimise pain and distress in the animal and to ensure safety of the person performing the euthanasia and often to protect other people and other animals.
It is imperative that personnel performing euthanasia on animals be trained. Training and experience should include familiarity with the normal behaviour of the species being euthanased, an appreciation of how handling and restraint affects that behaviour and an understanding of the mechanisms by which the selected technique induces loss of consciousness and death.
In evaluating the method of euthanasia, consider the following
1. Ability to induce loss of consciousness and death without causing pain, distress, anxiety or apprehension.
2. Time required to induce loss of consciousness.
4. Safety of personnel.
6. Compatibility with required purpose.
7. Emotional effect on observers and operators.
8. Compatibility with subsequent evaluation, examination of tissue etc.
9. Drug availability and human abuse potential.
10. Compatibility with species, age, and health status.
11. Safety for predators/scavengers should the carcase be consumed.
12. Is economical and readily available Animal Behaviour Considerations Gentle restraint (preferably in a familiar and safe environment), careful handling, and talking during euthanasia often have a calming effect on animals that are used to being handled. Preparation of observers should also be taken into consideration.
Native animals that are in the wild pose an additional challenge. When handling these animals, calming may be accomplished by minimising visual, auditory and tactile stimulation. Struggling during capture or restraint is often the norm as these animals are not used to humans.
Behaviour and physiologic response to noxious stimuli include distress vocalisation, struggling, attempts to escape, defensive or redirected aggression, salivation, urination, defecation, evacuation of anal sacs, pupillary dilation, tachycardia, sweating, and reflex skeletal muscle contractions causing shivering, tremors or other muscular spasms.
Fear can cause immobility or “playing dead” in certain species, particularly rabbits and birds. This immobility process should not be interpreted as a loss of consciousness when the animal is, in fact, conscious. Distress vocalisations, fearful behaviour, and release of certain pheromones by a frightened animal may cause anxiety and apprehension in other animals. Therefore, for sensitive species, it is desirable that other animals not be present when individual animal euthanasia is performed.
Human Behaviour Considerations Human psychological responses to euthanasia of animals need to be considered.
Grief at the loss of life is the most common reaction. There are six situations where people are affected by euthanasia of animals
1. Veterinary Clinic setting. Animals are euthanased under the best possible conditions with full understanding of procedures and counselling is often available to the carer.
2. Refuge situation where unwanted, homeless, diseased and injured animals must be euthanased in large numbers. Stress often develops among the volunteer helpers and there is often a need to frequently change the personnel.
3. Laboratory setting. Researchers, technicians and students often become attached to animals that have to be euthanased.
4. Wildlife situation. wildlife biologists, veterinarians, managers and carers are often responsible for euthanasia of animals that are injured, diseased, in excessive number or that threaten property or human safety. Although relocation of some animals is appropriate and attempted, relocation is only a temporary solution to a larger problem. People who must deal with these animals, especially under public pressure to save the animal rather than destroy them, can experience extreme distress and anxiety.
5. Livestock and poultry slaughter situation. A large number of animals processed daily can take a heavy toll on employees physically and emotionally. Federal and state agricultural employees may also be involved in mass euthanasia of poultry and livestock in the face of a disease outbreak or natural disaster e.g drought and floods.
6. Public exposure. Because euthanasia of zoo animals, animals involved in roadside or racetrack accidents, stranded marine animals, nuisance or injured wildlife and others can all draw public attention, human attitudes and responses should be considered whenever animals are euthanased.
Modes of action of euthanasing agents.
1. Hypoxia, direct or indirect. Agents that induce death by direct and indirect hypoxia can act at various sites and can cause loss of consciousness at various rates. For death to be painless and distress-free loss of consciousness should precede loss of muscle movement. Thus agents that produce paralysis without loss of consciousness (muscle relaxants, strychnine, nicotine and magnesium salts) are not acceptable
2. Depression of nerve cells in the brain causing loss of consciousness followed by death. Some of these agents release inhibition of motor activity during the first stage of anaesthesia, resulting in a so-called excitement or delirium phase, during which there may be vocalisation and some muscle contractions. These responses do not appear to be purposeful. Death follows loss of consciousness, and is attributable to cardiac arrest and/or hypoxaemia following depression of the respiratory centres.
3. Physical disruption of the brain activity, caused by concussion, direct destruction of the brain, or electrical depolarisation of neurones, induces rapid loss of consciousness. Death occurs because of the destruction of the midbrain centres controlling cardiac and respiratory function. Exaggerated muscle activity can follow loss of consciousness and, although it may disturb some observers, the animal is not experiencing pain or distress.
Euthanasia Agents Inhalant Agents: Requires special equipment, can be very effective. Most of these agents are hazardous to personnel because of the risk of explosion (ether) narcosis (halothane), hypoxia (nitrogen and carbon monoxide) and addiction (nitrous oxide)
1. Chloroform may be effective for very small birds, mammals and some small reptiles. It needs a small airtight container and an adequate amount of chloroform. Death can take up to 10 minutes
2. Carbon Monoxide (car exhaust) modern cars with catalytic converters are not as lethal producers of carbon monoxide, does cause sleep initially so is considered humane.
3. Carbon Dioxide as a euthanasing agent for small birds and mammals under 600 grams is being developed by WIRES in NSW using a small chamber and soda bulbs as a source. This looks like being their best solution for euthanasing small animals and birds.
Non-Inhalant Drugs: The use of injectable euthanasia drugs is the most rapid and reliable method of performing euthanasia. It is the most desirable method when it can be performed without causing fear or distress in the animal.
When the restraint necessary for giving an animal an intravenous injection would impart added distress to the animal or impose undue risk to the operator, sedation, anaesthesia, or an alternative route of administration should be employed.
When intravenous administration is considered impractical or impossible, intraperitoneal administration of a non-irritating agent is acceptable.
Lethabarb is quite alkaline and is often diluted with water or saline 50:50 so as not to cause any irritation when injected intraperitoneal.
Intramuscular, subcutaneous, intrarenal, intrasplenic intrathecal and other nonvascular injections are generally less acceptable.
Intrathoracic and intrapulmonary are sometimes employed but are generally frowned upon as they may cause the animal to cough.
When intraperitoneal injections are used animals may be slow to pass through stages 1 and 2 (sedation and excitement) of anaesthesia. Accordingly they should be placed in small cages in a quiet area to minimise excitement and trauma. The common agent used in Australia is a product called Lethabarb or Valabarb. These products contain approximately 5 times the strength of the Barbiturate that is found in a normal anaesthetic injection.
Barbiturates depress the nervous system in descending order beginning with the cerebral cortex, with loss of consciousness progressing to anaesthesia. With an overdose, deep anaesthesia progresses to apnoea, owing to depression of the respiratory centre, which is followed by cardiac arrest.
Advantages: With intravenous injection animals become unconscious in about 8 seconds and respiratory and cardiac arrest follow by about 15-20 seconds from commencement of injection. It is very smooth and there is minimal discomfort Disadvantages: Intravenous injection required for best results. Animals must be restrained. State laws restrict the use of these products to licensed Vets etc. These drugs may persist in the carcase and may cause sedation or death of animals that eat the carcase.
The advantages far outweigh the disadvantages. Intraperitoneal injections may be used in situations where an intravenous injection would be distressful or even dangerous.
Physical methods of Euthanasia
These methods include captive bolt, gunshot, cervical dislocation, decapitation, electrocution, microwave radiation, kill traps, thoracic compression, exsanguination, stunning and pithing. Many would consider most physical methods of euthanasia such as shooting, clubbing and flicking to be aesthetically displeasing and unacceptable.
When done appropriately with the right equipment and in the right situation some are considered acceptable. It cannot be done by the fainthearted.
Physical methods are harder for most carers as it requires a certain amount of resolve to do it and it is a very personal way to take a life Unacceptable methods of euthanasia include drowning, freezing, CO2 for any animal over 600g, decapitation or cervical dislocation for any mammal over 150 gram.
Chloroform or ether for microbats and reptiles as they can slow their breathing/metabolism, Exsanguination.
Wildlife For wildlife and feral animals, many recommended means of euthanasia for captive animals are not feasible. There are situations involving free ranging wildlife where euthanasia is not possible from the animal or human safety standpoint and killing may be necessary. Conditions found in the field, although more challenging than those that are controlled, do not in any way reduce or minimise the ethical obligations of the responsible individual to reduce pain and distress to the greatest extent possible during the taking of an animals life. Because lay personnel in remote settings often perform euthanasia of wildlife, guidelines are necessary to assist veterinarians, wildlife carers in developing humane protocols for euthanasia of wildlife.
Behavioural responses of wildlife to capture and close human contact are very different to those of domestic animals. These animals are usually frightened and distressed. Thus minimising the amount, degree, and/or cognition of human contact during procedures that require handling is of the utmost importance. Minimisation of auditory, visual and tactile stimulation will help ensure the most stress free euthanasia possible.