World Society for the Protection of Animals
Methods for the euthanasia of dogs and cats: comparison and recommendations This document aims to provide guidance on the
euthanasia of dogs and cats by identifying methods
considered humane and methods that might
compromise animal welfare.
The euthanasia of companion animals is a much
debated issue for animal welfare organisations around
the world. Opinions are diverse and are often influenced
by local situations and cultural backgrounds.
The decision to euthanase an animal is a complex
ethical matter involving many factors, and a detailed
discussion of the subject is beyond the scope of this
document. As an animal welfare organisation, it is our
obligation to ensure that when the decision to euthanase
is taken the methods used are truly humane and
administered by responsible and appropriately trained
Methods of euthanasia, scientific knowledge and
opinions evolve over time; this overview is based on
current scientific evidence and will be subject to review.
Author: Louisa Tasker, MSc, BSc (Hons.)Editor: Companion Animals Unit, World Society for the Protection of Animals World Society for the Protection of Animals 89 Albert Embankment London SE1 7TP T: +44 (0)20 7557 5000 F: + 44 (0)20 7703 0208 E: wspa@wspa-international.orgW: DISCUSSION OF
Criteria for euthanasia
Reasons for euthanasia
Personnel and training
Non-inhalant, injectable
Signs of pain and distress
pharmaceutical agents
Confirmation of death
Carcass disposal
Other intravenous anaesthetics Professional and sympathetic conduct
Potassium chloride (KCI) Magnesium sulphate (MgSO ) METHODS FOR THE
Chloral hydrate (CH) EUTHANASIA OF
Inhalant agents (gas mixtures)
General considerations Anaesthetic gases Summary table of methods:
Nitrogen or nitrogen/argon mixtures Recommended
Carbon dioxide (CO ) Acceptable
Carbon monoxide (CO) Conditionally acceptable
Nitrous oxide (N 0) Not acceptable
Physical methods
General considerations PRE-EUTHANASIA DRUGS
Shooting using a free bul et Sedatives
Combinations of pre-euthanasia drugs
General considerations REFERENCES
Dosages and routes of
administration of agents
for euthanasia of dogs and cats

Guidelines on the intravenous
injection of Pentobarbitone for
the euthanasia of dogs and cats

Criteria for euthanasia
Even when these components are in place, WSPA The term euthanasia comes from the Greek ‘eu' reluctantly accepts that there are circumstances when meaning ‘good' and ‘thanatos' meaning death, literal y the euthanasia of healthy animals is required, for translated it means ‘good death'. There are four example in the case of animals that cannot be rehomed, primary criteria that ensure death caused by methods or to avoid overcrowding in shelters that would of euthanasia is humane (Beaver et al., 2001). The compromise the welfare of animals being held there. WSPA firmly believes that in al situations when 1 Be painless
euthanasia is deemed necessary, the methods adopted 2 Achieve rapid unconsciousness fol owed by death
should meet al four of the criteria listed at the beginning 3 Minimise animal fear and distress
of this introduction, and hence be truly humane. 4 Be reliable and irreversible
Personnel and training
To meet these criteria, the method should take into Al methods of euthanasia have the potential to be account the species, age and health of the animal. In poorly performed if operators are untrained and addition the method should be simple to administer, unsupported. Consequently, it is essential that safe for the operator, as aesthetical y acceptable to the operators are provided with suitable training, including operator as possible, and preferably require smal doses a period of initial tuition with assessment of proficiency, of any chemicals used. fol owed by continuous monitoring of skil s and ability, as well as access to emotional support.
Reasons for euthanasia
A decision to euthanase an animal is a complex ethical
The initial period of instruction should, without matter involving many factors, and a detailed discussion exception, include training in both the technical aspects of the subject is beyond the scope of this document. of the methods to be used and the recognition of The World Society for the Protection of Animals (WSPA) signs of animal distress. Fol owing the instruction, believes euthanasia is acceptable and necessary when operators should understand the mechanism by an animal is suffering due to an incurable il ness or which that particular method of euthanasia causes injury, or when an animal presents a significant risk to unconsciousness and death. They should also receive human health and safety or the safety of other animals, direction and practical training in the careful handling through disease or aggressive behaviour. required to prevent distress in the animals they wil be restraining for euthanasia. It is essential that operators It is advisable for WSPA member societies, which may are taught to recognise the species-typical behaviour have cause to euthanase animals in their care, to adopt and physiological responses that indicate an animal is an agreed euthanasia protocol that clearly outlines the experiencing fear, distress, pain or anxiety, and how to reasons for euthanasia and the acceptable methods.
take immediate action to al eviate these states should they be observed. WSPA does not condone the mass destruction of dogs and cats as a population control measure. Signs of pain and distress
Successful control of dog and cat populations requires The fol owing behaviours or physiological responses a coordinated strategy that has been agreed by all may be signs of pain and distress: stakeholders and includes: Aggression towards humans or redirected towards self
Legislation with effective enforcement
or inanimate objects e.g. snapping, biting, growling, Registration coupled with a dependable method of
identification for dogs and cats Vocalisation whining, whimpering, high pitched
Reproduction control
barking, howling, or growling in dogs, hissing or yowling Measures to reduce the availability of dogs and cats
through the control of breeders, pet-shops and other Attempting to escape or withdraw from the situation
Education of owners or guardians so that they act as
responsible carers for their animals Pupils becoming dilated
Pilo-erection (hair standing on end)
• No animal should be disposed of until death is verified
Increased heart rate (tachycardia)
Shivering, muscle tremors and spasms; these may also
• Disposal should take into account regulations,
result from reflex skeletal muscular contractions disease control and drug residues
Immobility or freezing (the animal becomes tense and
Once death has been confirmed the animal should stops moving, but remains conscious and aware of the be disposed of in accordance with the local and/or national regulations. These rules should be obtained Urination
from the local municipality or relevant animal health/ environment departments in advance and all operators Anal sacs are emptied (foul smel ing liquid is
should comply with the necessary procedures. This is especial y important for disease control. Confirmation of death
Moreover, many of the injectable agents used for Al operators performing euthanasia should be able to euthanasia may leave residues in animal carcasses. identify when death has occurred. Indicators include: These drug residues may pose a threat to other animals in the event that the carcass is eaten and • No movement of the chest / No signs of respiration
may cause localised contamination upon carcass The animal's chest has stopped moving up and down indicating that it has stopped breathing.
DO NOT rely on this sign alone as the animal's
• Suspect rabies cases require cautious handling and
heart may continue to beat for some time after it
compliance with reporting regulations
has stopped breathing
Special precautions should be taken when handling the carcass of any animal suspected of carrying • No heart beat
rabies, including the use of protective clothing: Check for this with a stethoscope or by palpating gloves, overal s, eye goggles and protective shoes. the animal's chest wal .
The carcass should be sealed in a plastic bag, as • No pulse
the rabies virus can remain active for some time Check for this by palpation over the medial after death. The external surfaces of the carcass can aspect of the animal's hind limb. remain infective for several hours after death, and Not always easy to locate in small animals
the internal organs can remain infective for several weeks depending upon environmental temperature, • Loss of colour from the mucous membranes in the
so burial is not recommended. National or local animal's mouth
regulations may require that the carcass, head or Mucous membranes become pale and there is no a sample of brain tissue are sent to a public health capil ary refil if pressure is applied. With time the authority laboratory for testing and surveil ance. mucous membrane becomes dry and sticky.
Capillary refill is frequently still evident for
Professional and sympathetic conduct
prolonged periods after an animal has died
Al operators need to show professionalism and respect for animal welfare, for the value of animal life, and • Corneal reflex (blink reflex) is lost
for other people involved. The degree of distress that The corneal reflex is normal y elicited when the operators and other people experience when euthanasia eyebal is touched. After death, the animal's eyes is performed will be affected by their culture, beliefs remain open and the lids do not move when touched.
and the community in which they live. • Glazing of the eyes
Operators should be emotional y supported and trained This occurs rapidly after death. The cornea loses its to develop coping mechanisms to deal with this stress. clear, moist appearance and becomes opaque, dry This is important for many reasons, including the risk and wrinkled.
that dissatisfied personnel may become careless when handling animals and performing euthanasia. Ensuring that • Rigor mortis
the methods used are humane can also help to reduce the If death cannot be confirmed by a veterinary
distress experienced by operators and other people. surgeon, or there is any doubt, operators should
wait until rigor mortis has set in before disposing of
the animal's carcass.

The fol owing pages assess the methods of euthanasia
in current use, in terms of the effects on the animal and
additional information regarding usage. The methods are
divided into the fol owing categories:
This method is considered ‘best practice' because it consistently produces a humane death when used as the sole means of euthanasia.
These methods also produce a humane death when used as the sole means of euthanasia. However, there are practical limitations to their use.
These methods are acceptable only with caveats, due to the nature of the technique, potential for operator error, or safety hazards to personnel. These methods may not consistently cause death humanely.
These methods are inhumane and are not considered acceptable for the euthanasia of dogs and cats.
Some methods of euthanasia can be used in combination with pre-euthanasia drugs, and these are discussed after the summary table. A detailed overview of each euthanasia method, giving rationale for their categorisation, is provided on pages 15–21.
Intravenous (IV) injection of 20%
• egarded as ‘best practice'
Pentobarbitone solution
• apid loss of consciousness, followed by cardiac arrest • ay be used in combination with a pre-euthanasia drug if required for fearful, fractious or aggressive animals • o distressing side effects • equires training • elatively cheap • ot licensed for use in all countries • ost and availability may vary from country to country • ombinations of high concentrations of barbiturate with a local anaesthetic may also be available and suitable if given intravenously as a euthanasia agent ATS

Intraperitoneal (IP) injection of
20% Pentobarbitone solution
• akes longer to take effect than IV injection: 15–30 minutes (dependent upon the species and size of the animal) • larger dose may be required than if given intravenously • ay be used when col apsed or poor venous access precludes IV injection • ay not be suitable for the euthanasia of larger animals • he use of pre-euthanasia drugs may prolong the time until death • ay cause irritation to the peritoneum, particularly with concentrations >20%C • an be combined with a local anaesthetic to reduce the risk of irritation • nimal may become distressed when it starts to lose consciousness • ay be a practical alternative when IV injection is difficult e.g. for fractious stray or feral cats, neonatal kittens and puppies. It is advisable to return cats to a secure cage after injection as they may become distressed while the drug takes effect Intravenous (IV) injection of
anaesthetic agents, given as an
• apid loss of consciousness overdose
• ay be suitable if animals are already anaesthetised for surgery and, on humane grounds, not permitted to regain consciousness e.g. Thiopentone or Propofol; • elatively large volumes or high concentrations required to euthanase Thiobarbiturate or Phenol animals, potential y making it impractical for routine use depending upon the commercial availability of the preparationU • nder-dosing may lead to recovery • May be used in combination with a pre-euthanasia drug if required • equires training • ost may preclude routine use Intracardiac (IC) injection of 20%
• nly suitable in col apsed, unconscious animals, or very young puppies • ay be suitable if animals are already anaesthetised for surgery and, on humane grounds, not permitted to regain consciousness Only acceptable if animals are
• ntracardiac route may be painful in ful y conscious animals anaesthetised by other means prior
• equires training, skill and knowledge of anatomy to ensure penetration of to its administration (page 14)
the heart is successful on the first attemptS • ame licensing restrictions apply as with IV injection Oral (PO) administration of
• Takes longer to take effect than IV injection (over 30 minutes) • May be suitable for neonates (within the first few hours/days of life) as poor venous access precludes IV injection • Not suitable for the euthanasia of larger/older animals Only acceptable for neonatal
• May be used to sedate animals prior to euthanasia with intravenous animals or to sedate animals prior
injection of Pentobarbitone to intravenous injection of 20%
• Liquid form of the drug may be detected by animals in their food and ingestion is avoided • Powdered form may be delivered in gelatine tablets and hidden in food to encourage consumption • Animal may become distressed when it starts to become unconscious• Same licensing restrictions apply as with IV injection Intravenous (IV) injection of T61
in a controlled manner, after prior
• auses death by respiratory col apse due to paralysis of the diaphragm sedation
and intercostal muscles, resulting in asphyxia • equires slow, steady rate of injection Contains 3 drugs: general • recise rate of injection is required: its use in fractious animals is anaesthetic, local anaesthetic and • ntense pain may result if the injection is given too quickly, due to muscle paralysis prior to loss of consciousness Only acceptable if animals are
• t should never be used without prior sedation to permit slow rate of sedated by other means prior to its
administration and injection rate is
• equires training and skil slow (page 13)
• o longer available for use in the United States Intravenous (IV) or intracardiac
(IC) injection of potassium chloride
• auses death by cardiac arrest (KCl) after general anaesthesia
• t should never be used without prior general anaesthesia to achieve sufficient insensibility and analgesia, to block the painful side effects of Concentrated electrolyte solution • equires training to ensure operator can assess suitability of anaesthetic Only acceptable if animals are
depth prior to use of KCl anaesthetised by other means prior
• rior use of narcotic and analgesic mixtures adds significantly to the cost to its administration (page 14)
and prolongs the time of the procedure Intravenous (IV) or intracardiac
(IC) injection of magnesium
• auses death by cardiac arrest sulphate (MgSO ) after general
• t should never be used without prior general anaesthesia to achieve sufficient insensibility and analgesia, to block the painful side effects R • equires training to ensure operator can assess suitability of anaesthetic Concentrated electrolyte solution depth prior to its useL • arge volumes are required for euthanasia Only acceptable if animals are
• saturated solution is required but this makes the liquid very viscous and anaesthetised by other means prior
can result in difficulty of administration to its administration (page 14)
• rior use of narcotic and analgesic mixtures adds significantly to the cost and prolongs the time of the procedure Inhalation of gaseous anaesthetics
such as halothane, enflurane,
• equires high concentrations to be effective isoflurane and sevoflurane
• nly suitable for small animals (weighing <7kg) • ay be suitable if animals are already anaesthetised for surgery and, on Volatile inhalation anaesthetics humane grounds, not permitted to regain consciousness D • ifficult to administer to large animals • n un-anaesthetised animals the smel of the volatile agent may be unpleasant, such that they try to avoid it or hold their breath for a short timeI • n un-anaesthetised animals it may cause respiratory distress as many can act as irritantsC • an be harmful to operators: risk of narcosis if exposed to the volatile • ot routinely recommended as there are better alternatives Shooting a free bullet to the head
• an cause immediate insensibility if done correctly with an accurate shot Physical method • eath by physical damage to the central nervous system • nly acceptable in emergency situations where no other acceptable methods are possible because the animal cannot be handled or given pre-euthanasia drugs and it is necessary to al eviate the suffering of an • ot for routine use • equires training • equires skill and precision • ay require a licence: firearm use is likely to be subject to national and local regulations • ngerous and unpleasant for operator and any other persons present Intravenous (IV) injection of T61
• ay produce intense pain and causes death by paralysis of muscles when used alone
leading to asphyxiation prior to loss of consciousness if the injection rate is too quick Contains 3 drugs: general • ot acceptable when used alone for euthanasia anaesthetic, local anaesthetic and • o longer available for use in United States Intravenous (IV) injection of
• Cardiotoxic causes cardiac arrest without rendering the animal potassium chloride (KCl) given
alone or only with prior sedation
• Produces severe cardiac pain as a result• Sedation provides insufficient analgesia to block painful side effects of Concentrated electrolyte solution euthanasia agent • Not acceptable when used alone for euthanasia Intravenous (IV) injection of
• auses cardiac arrest without rendering the animal unconscious magnesium sulphate (MgSO )
• ay cause intense pain and distress given alone or only with prior
• edation provides insufficient analgesia to block painful side effects of euthanasia agentN • ot acceptable when used alone for euthanasia Concentrated electrolyte solution Oral (PO) or intravenous (IV)
administration of chloral hydrate
• eath results from depression of the central nervous system resulting in • esults in convulsions, muscular contractions and gasping Chemical reagent with sedative/ • istressing and painful side effects • arge volumes are required to be effective • ot acceptable for euthanasia Inhalation of nitrogen (N) or
nitrogen/argon mixtures
• eath due to hypoxia from paralysis of the respiratory centre • ypoxia may occur before loss of consciousness even at high concentrations, which is distressing for animalsV • ocalisation, convulsions and tremors have been observed prior to death • ery young animals (<four months) can take up to 30 minutes to die as they may be resistant to hypoxia • elfare aspects not entirely known • equires special y constructed chambers • equires a pure source of nitrogen/argon such as cylinder gas • ot recommended as better alternatives available Inhalation of carbon dioxide (CO )
• eath by asphyxia • ppears to be aversive in most species • cts as an irritant to the mucous membranes • nimals may experience pain and distress prior to loss of consciousness, associated with breathlessness, from increased concentrations of CO in the blood and acidosis Y • oung animals (<four months) are particularly resistant to hypoxia and may take longer to dieR • equires special y constructed chambers • equires a pure source of CO such as cylinder gas • ased upon current research to date on humans and other animals there are sufficient welfare concerns to indicate that this method should not be used for euthanasia Inhalation of carbon monoxide
• ighly variable time taken to lose consciousness and can take up to two minutes at 6% concentration • eath by hypoxia • ocalisations and agitation observed in dogs and this may occur while they are still consciousD • istressing side effects observed in cats during induction • nimals <4 months of age and sick or injured animals may have some resistance to hypoxia caused by exposure to COR • equires special y constructed chambers that are diligently maintained and are operated to safeguard animal welfare and human safetyR • equires a pure source of CO such as cylinder gas • otential danger to operators either through repeated exposure of low concentrations when operating the chamber or through accidental exposure to a lethal doseS • ufficient animal welfare and human safety concerns that this method cannot be recommended for euthanasia Inhalation of carbon monoxide
• n addition to above these are hot and contain irritant impurities (CO) exhaust fumes from petrol
• ot acceptable for euthanasia Inhalation of nitrous oxide (N 0)
• Death results from hypoxia • Used alone it does not cause anaesthesia• Causes respiratory distress before the animal loses consciousness • Requires large concentrations must maintain 100% concentration for • equires special y constructed chambers • equires a pure source of N O such as cylinder gas • uman health hazard if exposure occurs • ot acceptable for euthanasia Inhalation of Ether
• Causes death by hypoxia Inhalation agent • May cause respiratory distress • Irritants to the respiratory system • Requires large concentrations and rapid exposure to be effective • Requires special y constructed chambers• Highly inflammable and may be explosive dangerous to operators and al other persons present • Not acceptable for euthanasia Captive bolt
• though potential y and theoretical y an acceptable method this is not Physical method recommended for routine use due to practical difficulties including:R • equires skil and knowledge of anatomical variation in dog breeds e.g. dolichocephalic, brachycephalic, mesaticephalic skull typesA • nimal's head needs to remain steady to ensure accurate shot (this may be particularly difficult with cats)T • he bolt must be placed directly on to the animals skul • equires the animal to be restrained (this may be particularly difficult with • equires further procedure (pithing or bleeding) • isk of transmission of zoonotic disease (e.g. rabies) if exposed to blood/ • ay cause panic in waiting animals • ot recommended for euthanasia as other methods are more practicable • lthough it is theoretical y possible to apply a suitable current and voltage across the skull (so that it passes through the animal's brain) by trained Physical method personnel using suitable electrodes, it is WSPA's experience that such conditions are never achieved in practice • hole body exposure to the electric current in an electrocution chamber is • inful and inhumane under practical conditions • ngerous to personnel • ot acceptable for euthanasia • Slow acting• Death results from hypoxia Physical method • Pain and distress results from expanding trapped gases in the body prior to the animal becoming unconscious • Immature animals are tolerant of hypoxia and require longer periods of decompression before respiration ceases • Aesthetical y abhorrent as unconscious animals may bloat, bleed, vomit, convulse, urinate and defecate during decompression • Total y unacceptable • eath by asphyxiation from strangulation • auses fear and distress Physical method • otal y unacceptable Drowning
• rolonged death by asphyxiation caused by immersion in water Physical method • auses fear and severe stress • otal y unacceptable Strychnine
• rolonged time for the animal to die and this can be highly variable – from Poison: Neuromuscular blocker minutes to days depending upon the dose ingested • auses violent and painful muscle contractions resulting in asphyxiation • xtreme danger to personnel • otal y unacceptable • auses death by hypoxia and cardiac arrest • esults in violent convulsions and causes pain and distress while the animal remains conscious • xtreme danger to personnel • otal y unacceptable PRE-EUTHANASIA DRUGS
Pre-euthanasia drugs (tranquil isers, sedatives, action, hence this drug cannot be recommended for sole immobilisers or general anaesthetics) may be required use prior to euthanasia with agents that may cause pain. to facilitate safe and humane handling of animals Moreover ACP should not be used alone to calm fearful prior to euthanasia, particularly if they are fractious, animals prior to euthanasia with any, even non-painful aggressive or fearful. Moreover, the prior administration agent, as it does not alter the animal's perception of the of suitable pre-euthanasia drugs may be necessary with situation, merely its ability to respond.
some conditional y acceptable euthanasia agents to ensure they are humane. Sedatives
These drugs depress the activity of the central nervous
The majority of these drugs require minimal animal system, resulting in drowsiness and muscle relaxation so handling during their administration as they are that animals become uncoordinated. If they are given in preferably given as a subcutaneous injection (unless sufficiently high doses an animal may fal into a sleep-like contraindicated by the manufacturer), or sometimes as state. However, they may not render the animal insensible an intramuscular injection or even via oral dosing. The to pain: the animal general y remains conscious but operator then withdraws and waits for the drug to take calm. As with tranquil isers, sedated animals can become effect before administering the euthanasia agent. Some aroused by strong stimulation such as a painful procedure, pre-euthanasia agents, however, wil require intravenous making their behaviour unpredictable.
administration. An important point is that the use of these drugs can add significantly to the time taken to Examples of common sedative agents: perform euthanasia and this should be considered in Xylazine (Chanazine, Rompun, Virbaxyl, Xylacare)
advance to safeguard animal welfare. is a common sedative used with both large animals (equines and livestock) and smal (companion) animals. There are several drugs that are commonly used prior to It induces muscle relaxation and also possesses some euthanasia. It is essential that operators understand the analgesic properties. If used alone this drug may not be different effects each of these has on an animal, as their a suitable pre-euthanasia agent for some conditional y use may not be appropriate or humane as an adjunct to acceptable euthanasia methods, as it does not induce potential y distressing or painful euthanasia methods. sufficient anaesthesia. In addition this drug will cause a Terms such as tranquil isation, sedation, immobilisation drop in blood pressure, rendering subsequent intravenous and anaesthesia describe the actions of these drugs. injection of euthanasia agents more difficult.
These terms are sometimes incorrectly used as if they were interchangeable, their specific meaning and Medetomidine (Domitor) can induce sedation but must
different effects are explained below.
be given in a sufficiently large dose. Its use also results in muscle relaxation and provides some analgesia. As with Xylazine, if used alone this drug may not be a These drugs have some effects in decreasing fear and suitable pre-euthanasia agent for some conditional y apprehension while the animal remains awake, making acceptable euthanasia methods, as it does not induce it calm when exposed to low level stimuli. However, sufficient anaesthesia. Also as with Xylazine, this they have no analgesic effects and the animal is readily drug wil cause a drop in blood pressure, rendering aroused by painful stimulation. Often they give a false subsequent intravenous injection of euthanasia agents sense of security to someone handling an animal, which more difficult.
appears calm but may then display enhanced and even violent responses to a strong stimulus such as a loud Butorphanol (Torbugesic, Torbutrol) has some analgesic
noise or an approach by a person. This is potential y properties. But both its sedative and analgesic effects dangerous to anyone who has to perform euthanasia.
are dose dependent. However, this drug may not be suitable for sole use with some conditional y acceptable Example of common tranquil ising agent: euthanasia methods, as it does not induce sufficient Acepromazine maleate (ACP) is a common tranquil iser
anaesthesia or analgesia. Its use is unlikely to produce used in animals, and has some depressing effects the drop in blood pressure caused by Xylazine or on the central nervous system. Its principal use is in combination with other opiate drugs as a pre-medication given before anaesthesia. It wil not eliminate any pain associated with euthanasia agents, These drugs render the animal immobile by inducing and increasing the dosage above what is recommended paralysis. The animal's body may become rigid and stiff will have little further effect over the tranquil ising and the animal appears unresponsive to external stimuli such as sound. However, the animal can stil feel pain Oral administration of drugs or combinations of drugs and therefore the sole use of immobilisers with painful, as a prelude to euthanasia has been explored for dogs conditional y acceptable euthanasia agents is not (Ramsay and Wetzel, 1998) and cats (Wetzel and Ramsay, 1998; Grove and Ramsay, 2000). For dogs a combination of Tiletamine-Zolazepam/Acepromazine Example of common immobilising agent: or Pentobarbitone used alone consistently induced Ketamine (Ketaset, Vetalar) classed as a dissociative
sedation and lateral recumbency (Ramsay and anaesthetic, can also be used for restraint. It may Wetzel, 1998). However, the time taken to produce induce muscle rigidity when used alone and produces profound sedation was prolonged (3090 minutes) an altered state of consciousness (catatonia: not a loss and highly variable between individuals. of consciousness). Unless combined with other drugs such as Medetomidine, Xylazine and/or Butorphanol to In addition, the sole use of Pentobarbitone was produce sufficient analgesia and anaesthesia, it is not associated with struggling to stand and prolonged acceptable as a sole pre-euthanasia drug for use with ataxia during the onset of ful sedation. These euthanasia agents that may cause pain. Injection by undesirable effects were not observed for the intramuscular or subcutaneous routes may be painful Tiletamine-Zolazepam/Acepromazine combination and its rate of absorption can be altered. and they may be ameliorated if Acepromazine is added to the Pentobarbitone dose (Ramsay and Wetzel, 1998), but this combination was not tested. These result in loss of consciousness and provide It is important to note that liquid preparations of the good analgesia and muscle relaxation, so that surgical drugs mixed with food were detected and rejected procedures can be undertaken.
by dogs (Ramsay and Wetzel, 1998). Uptake by dogs was greatly improved when the required dose Examples of common anaesthetic agents: of powdered preparations was placed in gelatine Tiletamine-Zolazepam (Telazol®, Zoletil®). This drug
capsules and hidden in canned (wet) food. combination offers good anaesthesia and al ows for an intracardiac injection of pentobarbitone or intravenous The oral administration of Detomidine/Ketamine or intracardiac injection of conditional y acceptable combination was successful in sedating cats (Wetzel methods of euthanasia when properly administered. and Ramsay, 1998; Grove and Ramsay, 2000) This drug combination should be injected in comparison with other drugs tested (Ketamine, Detomidine, and Xylazine/Ketamine, Medetomidine/Ketamine combinations). This particular combination Thiopentone and Propofol. These drugs wil result in
produced reliable sedation within 1025 minutes sufficient anaesthesia to al ow for intracardiac injection of oral dosing (Grove and Ramsay, 2000). However of pentobarbitone or intravenous or intracardiac there are several undesirable side effects that may injection of conditional y acceptable methods of preclude this from routine use. The oral treatment of cats with all combinations tested (Detomidine/ euthanasia. However, both of these drugs must be given intravenously and may be unsuitable for use in animals Ketamine, Xylazine/Ketamine and Medetomidine/ that are difficult to handle or restrain.
Ketamine) resulted in vomiting and excessive salivation in some cats (Wetzel and Ramsay, 1998; Combinations of pre-euthanasia drugs
Grove and Ramsay, 2000) and is likely to cause Combinations of drugs may enhance their suitability distress to cats during induction prior to loss of as a prelude to euthanasia, especial y if they possess different, complementary analgesic and anaesthetic properties (e.g. Ketamine and Butorphanol). Such Food dosed with these types of drug is unpalatable, combinations should be chosen to render the animal hence precluding accurate administration via food. insensible to the pain that may result from some However, the method of dosing used in these tests conditional y acceptable euthanasia methods. When (squirting the liquid medicants directly into the cats' using a combination of drugs it is vital that a sufficient mouth) is difficult to perform remotely with any dose of each drug is used, and that ample time is accuracy. The handling of fractious or aggressive cats al owed for them to reach their maximum effect before for oral dosing is likely to cause stress to the animals, euthanasia is undertaken. Moreover, animals should be thus presenting a welfare issue as wel as a potential maintained in a quiet and calm environment as external hazard for operators. Furthermore, Detomidine may stimulation can prolong the time taken for drugs to not be licensed for use in cats and guidelines for off- take effect. Both of these factors can be affected label use should be fol owed.
by an animal's species (dog or cat), age, body size, demeanour and metabolism, so the individual animal's drug requirements must be careful y determined before this course of action. DISCUSSION OF
The fol owing discussion provides greater detail expression of pain. In some individuals a terminal regarding the use and suitability of each method gasp may occur when the animal is unconscious and described in the summary table, to explain the reasons although this may distress some observers, it is not an for their categorisation. They are arranged by mode of expression of pain or discomfort, merely a reflex action. action and their acceptability for euthanasia. Pentobarbitone is easy to use, relatively cheap and safe for the operator (provided that it is not misused, e.g. Euthanasia agents are general y classified by their physical deliberately self-injected). characteristics: non-inhalant (injectable) pharmaceutical agents; inhalant agents (gas mixtures); physical When the restraint necessary for giving an intravenous methods; and poisons. They work by one of three modes injection would distress an animal or pose undue risk of action (Close et al., 1996; Beaver et al., 2001): to the operator then prior sedation or anaesthesia (pages 13–14) or other accepted alternative routes of • Hypoxia – death results from reducing the amount of administration should be employed (Beaver et al., 2001). oxygen available to the animal's cel s and tissues.
In an emergency situation the drug can be injected • Direct depression of the nerve cel s in the respiratory directly into the peritoneal cavity (intraperitoneal). centres of the brain necessary for maintaining life The time taken for the animal to lose consciousness function, leading to a loss of consciousness fol owed and die (15–30 minutes) is longer than if the drug is given intravenously (a few seconds). A higher dose of Pentobarbitone is required for intraperitoneal • Physical disruption of brain activity through euthanasia (Grier and Schaffer, 1990; Sinclair, 2004) concussion, direct destruction of the brain, or and it can cause irritation to the peritoneum, but this electrical depolarisation of nerve cel s, leading to can be avoided if the drug is combined with a local rapid unconsciousness. Death occurs owing to destruction of the areas of the brain that control cardiac and respiratory functions. There are no published reports on the use of intraperitoneal injection in dogs; nevertheless Sinclair (2004) provides anecdotal accounts that dogs Non-inhalant, injectable
struggle more than cats; repeatedly attempting to right themselves during the induction phase. For this Barbiturate, injectable anaesthetic agents,
reason intraperitoneal injection may be unsuitable for T61, potassium chloride, magnesium sulphate
larger animals.
and chloral hydrate
While most cats, kittens and puppies appear to advance more smoothly to unconsciousness than adult dogs, they should be closely monitored, and confined to a warm, dark, quiet place to facilitate distress-free induction. Barbiturates act by depressing the central nervous The combination of Pentobarbitone and Phenytoin (a system, starting with the cerebral cortex, which cardiotoxic anticonvulsant drug) may be unsuitable causes rapid loss of consciousness progressing to for intraperitoneal injection, because of concerns over anaesthesia (Beaver et al., 2001). Their efficacy as the differential absorption rates of the two compounds anaesthetic agents free from distressing side effects is (Sinclair, 2004). The effects of Phenytoin on the heart widely recognised. With sufficient dosages (overdose) may occur before the Pentobarbitone component has barbiturates induce respiratory and cardiac arrest caused unconsciousness (Fakkema, 1999 cited by by depressing the centres within the central nervous Sinclair, 2004). system that control these life-maintaining functions. The technique for intrahepatic injection of For euthanasia of dogs and cats, barbiturates that Pentobarbitone has been reported by Grier and have been specifical y formulated as euthanasia Schaffer (1990). When correctly administered, agents are preferred. The intravenous injection of 20% its action is considerably faster in comparison to Pentobarbitone solution is regarded as the most humane injection via the intraperitoneal route, with cardiac method of euthanasia for dogs and cats (Reil y, 1993; standstil being reported within 11–14 minutes. Close et al., 1997; Beaver et al., 2001; European Food However, performing accurate intrahepatic injection is Safety Authority, 2005) (see Annex 2). Dogs and cats technical y difficult and may cause animals discomfort are simply ‘put to sleep'; there is no audible or other (Sinclair, 2004). Administration outside of the target organ (the liver) is associated with excitement, which inducing unconsciousness and death. However, may also be distressing to the operator (Grier and larger volumes are required for euthanasia (Annex 1) Schaffer, 1990). and often this makes their use more cost prohibitive for routine euthanasia than Pentobarbitone. In Injection of 20% Pentobarbitone directly into the heart addition these agents should not be given other than (intracardiac) may be suitable in col apsed, unconscious intravenously, as they may cause tissue reactions at animals. However, this requires skil and knowledge of the site of injection leading to pain and discomfort. As anatomy because failure to inject into the correct place with Pentobarbitone, they may be subject to restricted wil cause pain. It should only be used by experienced licensing practices. technicians in an emergency. It may be appropriate to administer liquid form of a ACCEPTABLE WITH CONDITIONS
suitable concentration of Pentobarbitone oral y (by mouth) to neonatal puppies and kittens (within the first T61 is a mixture of three compounds (embutramide, few hours/days of life) for euthanasia, as intravenous mebezonium iodine, tetracaine hydrochloride), access is difficult. The time taken for effect is longer which provide a combination of muscle paralysis than if administered intravenously. (via curarifrom-like mechanisms), local anaesthetic and general anaesthetic actions (Giorgi and Bertini, It should be noted that the time taken for oral 2000). The muscle paralysing agent rapidly administration of Pentobarbitone to reach its maximum induces respiratory col apse by paralysing the effect is prolonged (30–90 minutes) and highly variable animals' diaphragm and intercostal muscles. A between individuals given the same dose (Ramsay and local anaesthetic acts to reduce (painful) tissue Wetzel, 1998). In addition to the lengthy induction inflammation at the site of the injection, and the time, other undesirable side effects may make this general anaesthetic induces loss of consciousness.
method unsuitable for routine use, for instance some dogs may struggle prior to becoming ful y sedated The three compounds have different speeds of (Ramsay and Wetzel, 1998). absorption in the body (Beaver et al., 2001) and there is a risk that if the injection is given too quickly Oral administration of Pentobarbitone for euthanasia the animal wil remain conscious during respiratory of juvenile or adult dogs and cats is unsuitable. col apse, which may produce pain (Giorgi and Bertini, It may, however, be used to produce sedation or 2000) and distress (Hel ebrekers et al., 1990) prior light anaesthesia to precede intravenous injection to death. For this reason T61 should be given by a of Pentobarbitone for the euthanasia of fractious or slow and precise rate of intravenous injection (Beaver aggressive animals (Ramsay and Wetzel, 1998; et al., 2001). This is likely to be difficult with animals Sinclair, 2004). that are anxious when being handled or restrained. Some euthanasia products have been formulated to use T61 should therefore only be used with prior sedation barbiturates combined with a local anaesthetic agent (page 13) to al ow for close monitoring of injection or Phenytoin. The pharmacological differences are rate and to avoid causing pain to the animal. It should inconsequential when injected intravenously but such never be given other than intravenously (Annex 1), as compounds may be more easily obtained in the onset of action of each of the three constituents can be altered when administered via alternative routes (Beaver et al., 2001). T61 is no longer WSPA considers the use of intravenous Pentobarbitone available for use in the United States. for euthanasia of dogs and cats as ‘best practice' (Annex 1, Annex 2) and its use is strongly ACCEPTABLE WITH CONDITIONS
recommended provided that it is legal y permissible and operators have been given appropriate training. Potassium chloride (KCI)
However, suitable barbiturates are not always The potassium ion is cardiotoxic (has a toxic effect available and in these circumstances WSPA urges on the heart muscle) and rapid injection of potassium veterinary authorities, animal welfare organisations and chloride (KCI) as a saturated salt solution causes governments to strive to make these drugs legal y and cardiac arrest leading to death if given intravenously easily available to the relevant professionals. or by the intracardiac route of injection. It has no anaesthetic or analgesic properties so if used alone it causes animals intense pain prior to death. Hence KCI is only acceptable as the final stage of euthanasia Other intravenous anaesthetics
in animals given prior narcotic or analgesic agents to Other barbiturate drugs commonly used as block its painful side effects (page 14). It is essential anaesthetics, such as Thiopentone and newer agents that personnel performing this technique are trained such as Propofol, wil produce painless euthanasia if and knowledgeable in anaesthetic techniques. They given intravenously as overdoses (Annex 1). They work should be competent at assessing anaesthetic depth in a similar manner to that described above, rapidly appropriate for subsequent administration of KCI. Euthanasia with KCl is only considered to be acceptable Inhalant agents (gas mixtures)
if animals are under general anaesthesia, characterised Anaesthetic gases, nitrogen/argon, carbon dioxide,
by loss of consciousness, loss of response to unpleasant carbon monoxide, nitrous oxide and ether
(including painful) stimuli and an absence of reflex muscle responses (Beaver et al., 2001). KCI can be General considerations easily acquired, transported and mixed with water to Inhalation agents used for euthanasia include volatile form an injectable, supersaturated solution (Annex liquid anaesthetics and gases or gas mixtures that result 1) to kill animals. However, the use of suitable pre- in hypoxia; delivered at increasing concentrations they euthanasia drugs wil significantly increase both the displace oxygen in the air breathed by animals (inspired time taken to perform euthanasia and its cost. air) thereby lowering the concentration of oxygen reaching the lungs and tissues (Close et al., 1996). ACCEPTABLE WITH CONDITIONS
To be effective, inhaled agents must reach a certain Magnesium sulphate (MgSO )
(minimum) concentration in the animal's lungs (Beaver et Magnesium sulphate (MgSO ) is a neuromuscular al., 2001). This means they do not induce an immediate blocking agent. If delivered intravenously as a saturated loss of consciousness, and death fol ows at some salt solution it wil lead to cardiac and respiratory arrest considerable time later (European Food Safety Authority, fol owed by death (Close et al., 1996). However, it 2005). The humane induction of unconsciousness is causes muscle paralysis (inducing respiratory arrest) important, and any inhalation agents used must not without prior loss of consciousness (Beaver et al., be unpleasant for the animal to breathe or produce 2001); the animal therefore remains conscious but pain or distress prior to loss of consciousness (Close immobile until the brain succumbs to lack of oxygen et al., 1996, 1997; Leach et al., 2004; European Food (European Food Safety Authority, 2005). Moreover Safety Authority, 2005). In particular, inhalation agents MgSO has no analgesic or anaesthetic properties that produce convulsions prior to unconsciousness are to block the painful side effects and its sole use as unacceptable for euthanasia and should not be used an agent for euthanasia is inhumane (Close et al., (Close et al., 1996; Beaver et al., 2001).
1996, 1997; Beaver et al., 2001; European Food Safety Authority, 2005). Dogs have been observed to Very young animals are particularly resistant to the experience violent muscle spasms and contractions, effects of lowered oxygen concentrations (hypoxia/ vocalising, gasping for breath and convulsion seizures anoxia) because their haemoglobin (the oxygen- prior to death (Avariez and Caday, 1958), indicating transporting molecule in red blood cel s) has a higher that they experience pain and distress. As with affinity for oxygen than that of adults (Pritchett et al., using KCI for euthanasia, MgSO is only acceptable 2005 cited by European Food Safety Authority, 2005); as the final stage of euthanasia in animals that are an adaptation to being in the uterus. Young animals, anaesthetised (page 14) and hence unconscious and therefore, take longer to die from hypoxia than adults unresponsive to noxious (including painful) stimuli (and (Close et al., 1996; Beaver et al., 2001). their reflex muscle responses can no longer be evoked). Again, this requirement for pre-euthanasia drugs Inhaled agents may take longer to build up in the lungs significantly adds to both the time taken to perform and be effective in animals that are il , injured or old, as euthanasia and to its cost. Furthermore, large volumes these animals may show decreased ventilation (shal ow of MgSO are required (Annex 1) and an effective breathing), making agitation more likely before loss of saturated solution becomes very viscous and difficult to consciousness (Beaver et al., 2001).
handle for injection. In addition to these general considerations for animal welfare, the health and safety of operators is a major concern with some of these methods. Both acute and Chloral hydrate (CH)
chronic exposure to these agents can have toxic effects Chloral hydrate (CH) acts slowly to depress the brain on humans (National Institute for Occupational Safety centres responsible for control ing respiration and and Health, 1977). during the time taken to become unconscious animals display muscle spasms, gasp for breath and vocalise; indicating that they are in distress (Carding, 1977; ACCEPTABLE WITH CONDITIONS
Close et al., 1996). This drug has no anaesthetic or Anaesthetic gases
analgesic properties to block the painful and distressing Halothane, Enflurane, Isoflurane and Sevoflurane are side effects and it is unacceptable for use in dogs and commonly used as anaesthetic agents and can be cats. Even with prior use of anaesthetics its slow mode used for euthanasia if they are given as an overdose of action and the large volume required for it to be (Annex 1) (European Food Safety Authority, 2005). effective make it unacceptable for euthanasia (Carding, However, these agents differ in the speed at which 1977; Beaver et al., 2001).
they induce unconsciousness and they possess varying degrees of pungency, which animals may find unpleasant (Leach et al., 2004; European Food Safety Authority, 2005). In addition, animals may struggle and loss of consciousness, dogs were observed yelping, become anxious during induction (Beaver et al., 2001) gasping and convulsing, and some develop muscle because anaesthetic vapours may be irritating (Leach et tremors (Herrin et al., 1978), occurrences likely to al., 2004). They are therefore not general y considered be aesthetical y objectionable for human operators to be suitable as sole agents for euthanasia in larger (Reil y, 1993; European Food Safety Authority, 2005). animals (>7kg). Halothane is preferred because it may Although time to unconsciousness was 1–2 minutes be less aversive during induction (Leach et al., 2004) from initial exposure to the gas, the time to death was and produces anaesthesia more rapidly than the other recorded at 5 minutes (Herrin et al., 1978). Tranquil ising agents (Beaver et al., 2001; European Food Safety dogs with Acepromazine (ACP) prior to exposure with Authority, 2005). nitrogen gas for euthanasia (in an attempt to ameliorate the possible distressing side effects of hypoxemia) Inhalation anaesthetic agents are vaporised and significantly prolongs the time to death (Quine et al., delivered into chambers, via a face mask or tube from 1988). It is essential that high concentrations of gas anaesthetic machines; they are combined with air/ are maintained for the duration until death has been oxygen during induction to prevent hypoxia (Close confirmed (European Food Safety Authority, 2005), as et al., 1996, Beaver et al., 2001). The liquid states re-establishing concentration of oxygen at 6% or greater of these agents are highly irritant, and animals in the chamber will al ow immediate recovery (Beaver et should only be exposed to vapours. Chambers and al., 2001).
anaesthetic machines should be properly designed to ensure that the gas is evenly distributed and that the In summary, the suitability and humaneness of this animal is rapidly exposed to effective concentrations method is not well understood (Beaver et al., 2001; of the agent (Close et al., 1996). It is important to European Food Safety Authority, 2005). Current evidence use equipment that is wel maintained and to have indicates this method is unacceptable because animals scavenging units (devices used to reduce the pol ution may experience distressing side effects prior to loss of in the air) to prevent personnel being exposed to the consciousness, and there are more humane alternatives anaesthetic agents, as exposure to trace concentrations available for the euthanasia of dogs and cats. of anaesthetic gases is recognised as a human health hazard (National Institute for Occupational Safety and Health, 1977).
Carbon dioxide (CO )
The large doses required for euthanasia are expensive Carbon dioxide (CO ) is a non-flammable, non-explosive and tend to make this method cost prohibitive. With gas, present in air in smal concentrations (0.04%); as a the difficulty in administration and human health separate gas it is heavier than air (Carding, 1977; Beaver aspects, this means that although this can be an et al., 2001). Inhalation of CO above 70% depresses acceptable method of euthanasia for smal dogs and the central nervous system leading to respiratory arrest cats there are more suitable methods available (Close and death from asphyxia (Carding, 1968). Depending et al., 1997; Beaver et al., 2001). The greatest value on the concentration, loss of consciousness may occur of anaesthetic gases may be for the euthanasia of smal within 12 minutes but actual death may not fol ow until animals (<7kg) where intravenous access is difficult, 5–20 minutes after initial exposure (Carding, 1968). and to al ow for intracardiac injection of other suitable For euthanasia, CO must be delivered at a control ed euthanasia agents. In addition, anaesthetic gases may rate from cylinders into special y constructed chambers be given as an overdose to animals that are already (Beaver et al., 2001).
surgical y anesthetised when, on humane grounds, it is not desirable for them to regain consciousness.
CO is aversive to most species (European Food Safety Authority, 2005). Concerns over the humaneness of CO (European Food Safety Authority, 2005) stem from its association with breathlessness and hyperventilation Nitrogen or nitrogen/argon mixtures
(Hewett et al., 1993; Raj and Gregory, 1995). At high Nitrogen and argon are colourless, odourless gases concentrations, CO dissolves in the moisture of the that are inert, non-flammable and non-explosive. animal's air ways producing carbonic acid that causes Both gases are present in atmospheric air (nitrogen at irritation (Ewbank, 1983, Close et al., 1996) and pain 78% and argon at <1%). Placing animals in enclosed in the animal's nose (Beaver et al., 2001). In cats, containers that are pre-fil ed with nitrogen or argon induction to unconsciousness is accompanied by escape induces unconsciousness and results in paralysis of the attempts, licking, sneezing and increased movement or respiratory centres, fol owed by death (Beaver et al., agitation (Simonsen et al., 1981); indicating exposure is 2001; European Food Safety Authority, 2005). distressing (Close et al., 1997). Similarly, in dogs rapid exposure to increasing concentrations of CO produced There are few studies on nitrogen inhalation for severe struggling and hyperventilation (Carding, 1968).
euthanasia of dogs, but these suggest that loss of consciousness is preceded by hypoxemia and Studies conducted in rats have concluded that CO hyperventilation (Herrin et al., 1978) which may be when used in concentrations sufficient to induce loss of distressing to animals (Beaver et al., 2001). Fol owing consciousness are likely to cause considerable suffering before unconsciousness (Danneman et al., 1997; Leach There are several practical limitations associated with et al., 2004). The cumulative stress associated with the this method of euthanasia. Firstly, the construction, induction of unconsciousness when using CO is a serious diligent maintenance and careful operation of special welfare concern (European Food Safety Authority, 2005). chambers are essential to reduce the risk to human WSPA therefore considers this to be an unacceptable and animal welfare; and these are likely to be costly. method for the euthanasia of dogs and cats. Secondly, use of CO to euthanase certain groups of animals is considered unacceptable (Humane Society of the United States, undated). In particular, animals under four months old (resistant to hypoxia); those Carbon monoxide (CO)
with impaired breathing and or low blood pressure Methods of generating carbon monoxide (CO) gas (due to systemic disease, injury or old age) wil take for euthanasia of animals have included chemical longer to succumb, causing additional distress prior interaction arising from combining sulphuric acid to death. Use of CO inhalation to euthanase obviously and sodium formate and the use of exhaust fumes pregnant animals is also discouraged as the unborn produced from idling petrol engines (Carding, 1977). young wil not be exposed to the gas and wil die slowly Both of these techniques produce irritants that are as a result of suffocation, due to death of the mother likely to result in considerable distress to animals and (Humane Society of the United States, undated). are therefore detrimental to the welfare of dogs and Moreover, unconscious dogs urinate, defecate and cats (Carding, 1968, 1977; Close et al., 1996; Beaver regurgitate (Moreland, 1974) making this aesthetical y et al., 2001), and hence their use is not acceptable. objectionable for operators and requiring chambers to Commercial y compressed CO delivered from cylinders be thoroughly cleaned, adding to the time of use. into special y constructed chambers has been used for the mass euthanasia of dogs and cats.
Although considered a conditional y acceptable method of euthanasia by the American Veterinary Medicine CO combines with haemoglobin in the red blood Association (Beaver et al., 2001) and the Humane cel s, decreasing the oxygen carrying capacity of the Society of the United States for some dogs and cats, animal's blood. As a result, less oxygen is delivered the many limitations of CO may make this method less to the tissues and cel s (hypoxia), which leads to practical, considerably slower and more expensive than unconsciousness, fol owed by death (Chalifoux lethal injection (Humane Society of the United States, and Dal aire, 1983). Although the animal becomes undated). There is also concern over the distressing unconscious within 1–2 minutes (variable between side effects of exposure to CO (European Food Safety individuals), death as confirmed by cessation of Authority, 2005) while the animal is conscious (Stafford, heartbeat does not occur until 10–20 minutes after 2006) and over the significant danger to operators. For initial exposure to CO at concentrations reaching these reasons WSPA considers this to be an unacceptable 6% (Moreland, 1974; Chalifoux and Dal aire, 1983; method for the euthanasia of dogs and cats.
Dal aire and Chalifoux, 1985). Although the welfare aspects of this method have not been wel researched, a few studies have reported that prior to loss of consciousness dogs show signs of anxiety, including Nitrous oxide (N 0)
moaning vocalisations (Carding, 1968; Chalifoux and This gas is no longer considered appropriate as a sole Dal aire, 1983; Dal aire and Chalifoux, 1985) and anaesthetic agent as it does not induce anaesthesia signs of agitation (Moreland, 1974; Chalifoux and in animals even at 100% concentrations (Beaver Dal aire, 1983). Furthermore, there is some concern et al., 2001). If N 0 is used on its own it produces that the onset of convulsions (Close et al., 1996) and hypoxemia (low oxygen in the blood) (European Food muscular spasms (Moreland, 1974) may precede loss Safety Authority, 2005) before respiratory or cardiac of consciousness (Chalifoux and Dal aire, 1983; Close arrest (Beaver et al., 2001) and as a result animals et al., 1997). Equal y distressing behaviours have been may become distressed prior to loss of consciousness observed in cats during the initial phase of euthanasia (Beaver et al., 2001). This method is considered using this method (Simonsen et al., 1981).
inhumane and not acceptable for euthanasia.
Use of the tranquiliser ACP prior to euthanasia with CO significantly reduced some of the behavioural and physiological responses of dogs, but sufficient time must be al owed for ACP to reach its maximum effect This is a highly inflammable volatile liquid, which may before exposure to CO (Dal aire and Chalifoux, 1985).
be explosive under some circumstances. It must be vaporised by the passage of a gas, normal y oxygen, In addition to the risks for animal welfare, CO is to be used as an anaesthetic. Ether is a relatively extremely hazardous for humans because it is highly dangerous substance to use and causes distress by toxic and difficult to detect. Even chronic low level irritation to the nasal passages and eyes to both the exposure is considered a human health hazard and is animal and the operator (Close et al., 1996). This agent associated with cardiovascular disease (Beaver et al., is not suitable for euthanasia, because of extreme risk to operators and the detrimental effects on animal welfare.
Physical methods
the conformational differences between the skul s of Shooting using a free bullet, penetrating captive bolt,
individuals and breeds of dogs increase the risk of a electrocution, decompression, hanging and drowning
mis-stun. The principle skull types are dolichocephalic (long, narrow head), brachycephalic (short, wide heads) General considerations and mesaticephalic (medium proportions).
For several reasons physical methods for the euthanasia of dogs and cats are general y not recommended Use of a captive bolt may be aesthetical y unpleasant (Close et al., 1997). Some methods are likely to cause to the operator, especial y as further measures are severe pain and suffering to animals and are therefore necessary (e.g. pithing or exsanguination) to ensure death considered inhumane, and unsuitable for euthanasia. In (Beaver et al., 2001). The bleeding that occurs after addition the high risk of equipment failure, malfunction penetration of the skul and after further pithing creates and operator error when used in practice wil cause a hazard for the operator, due to the risk of coming into pain and distress to the animals. The only physical contact with blood and brain matter. This risk may be of method considered conditional y acceptable by WSPA particular concern in rabies-endemic areas.
shooting with a free bul et could be used as a last resort in an emergency situation when no other As there is a high risk of mis-stunning through inadequate methods are possible, but not as routine. use of the penetrating captive bolt, and hence causing pain and distress, WSPA considers this an unacceptable Many of these methods may be aesthetical y method for the euthanasia of dogs and cats. objectionable for personnel, making them distressing to perform and further increasing the stress that operators may experience. Furthermore, if operators are distressed and dissatisfied themselves, there is an increased likelihood of them becoming careless when In theory it is possible to achieve euthanasia by handling animals. applying an appropriate electric current and voltage in a two-step process: first, spanning the animal's ACCEPTABLE WITH CONDITIONS
brain to render it unconscious – producing an effective stun; second, applying sufficient current across Shooting using a free bullet
the heart to produce cardiac fibril ation and death An accurate shot to the animal's head wil result from hypoxia (Beaver et al., 2001). However, it is in immediate destruction of the brain and loss of WSPA's experience that such ideal conditions are consciousness, fol owed by death (Carding, 1977). never achieved in practice. There are grave concerns However, specialist training and considerable skill over the suitability of the design (Carding, 1977) is required to ensure that the bul et wil penetrate and maintenance of equipment, which, coupled with the brain. In addition there is extreme danger to the lack of training and misuse (Phil ips, undated), make operators and any bystanders, and a firearm should this method inhumane. If an animal is not effectively never be used in enclosed spaces as there is a risk stunned, which is often the case with whole body of ricocheting bul ets. Moreover, the use of a firearm exposure to electric current in electrocution chambers is likely to be subject to strict local and national (Carding, 1977), death results from cardiac fibril ation regulations. WSPA would only conditional y accept in a conscious animal, and hence involves excruciating this method for use in an emergency situation, when it pain and distress. In addition this method may be is necessary to al eviate the suffering of an individual extremely hazardous to personnel, and is aesthetical y animal but no acceptable euthanasia methods are objectionable as it causes violent extension and possible, because the animal cannot be handled or stiffening of the animal's limbs, head and neck given pre-euthanasia drugs.
(Beaver et al., 2001).
WSPA regards electrocution as an unacceptable method of euthanasia for dogs and cats, as the minimum Captive bolt
conditions necessary for it to be humane are often not Although widely used and accepted as a stunning achieved in practice. procedure for the slaughter of large livestock species, this method is general y considered inappropriate for dogs and cats (European Food Safety Authority, 2005). The penetrative captive bolt pistol must be placed in contact with the animal's skull and precise positioning This method requires the use of decompression is essential so that the bolt penetrates the correct area chambers. In theory the low ambient air pressure in of the brain first time. Animals must be adequately the absence of extra oxygen results in cerebral hypoxia, restrained so that the head remains steady (Carding, leading to loss of consciousness fol owed by death 1977; Dennis et al., 1988; Beaver et al., 2001), which (Carding, 1977). However, expansion of trapped gases makes this method particularly difficult with fearful and in body cavities leads to adverse physical effects, pain aggressive dogs and cats (Carding, 1977). Furthermore, and discomfort (Close et al., 1996), and is likely to cause anxiety and stress in animals (Close et al., 1997). In addition this method may be aesthetical y unpleasant for the operator as unconscious animals may bloat, bleed, vomit, convulse, urinate and defecate during decompression (Hatch, 1982).
This method is inhumane and therefore not acceptable for the euthanasia of dogs and cats.
Death results by asphyxiation from constriction of the
trachea after strangulation, causing the animals fear
and distress. This method is inhumane and its use is
condemned by WSPA.
Prolonged death by asphyxiation after immersion in
water (drowning) causes animals fear and severe stress
(Close et al., 1996). This method is inhumane and its
use is condemned by WSPA.
Strychnine and cyanide

General considerationsThese agents cause excruciating pain and distress to animals. Strychnine
Strychnine acts on the nervous system resulting in
painful muscle contractions and violent convulsions. The animal remains conscious and experiences extreme pain and distress before it dies as a result of suffocation (Lumb, 1985; Close et al., 1996; Beaver et al., 2001). This is an unacceptable agent for euthanasia as its mode of action is inhumane.
The World Society for
the Protection of Animals
firmly believes that in all
situations when euthanasia
Cyanide blocks oxygen uptake, leading to respiratory is deemed necessary the
col apse. It is accompanied by violent and painful methods adopted should be
convulsions prior to the onset of unconsciousness and death (Hatch, 1982). In addition, the use of cyanide truly humane. They should
represents an extreme danger to people as they are achieve rapid, painless
equal y susceptible to its toxicity. The use of cyanide is death and minimise fear
inhumane and should never be a method of euthanasia. and distress to animals. Our
goal is for all countries to
adopt the humane methods
endorsed by WSPA, and for
this document to be used
to encourage authorities to
make the recommended
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Grove, D.M. and Ramsay, E.C. 2000. Sedative and physiological effects of oral y administered ά2–adrenoceptor agonists and ketamine in cats. Journal of the Stafford, K. 2006. Free living dogs. In: The welfare of dogs, pp: 31–54. Springer, American Veterinary Medical Association 216: 1929–1932.
Dordrecht, The Netherlands.
Hatch, R.C. 1982. Euthanatizing agents. In Veterinary Pharmaceuticals and Wetzel, R.W. and Ramsay, E.C. 1998. Comparison of four regimens for intraoral Therapeutics. (eds. N.M. Booth and L.E. McDonald), fifth edition, pp. 1059–64. administration of medication to induce sedation in cats prior to euthanasia. Journal Ames, Iowa State University Press, USA. of the American Veterinary Medical Association 213: 243–245.
ANNEX 1: Dosages and routes of administration of
agents for euthanasia of dogs and cats
The information is from those organisations using drugs for euthanasia in the field. The effects of many of these agents are dose dependent. It is therefore essential that an accurate estimate of the animal's weight is obtained prior to euthanasia. In addition the effects of these drugs may be highly variable and dependent upon the individual animal's physical characteristics and circumstances. Al manufacturers' instructions should be consulted and adhered to.
Use of pre-euthanasia
drugs indicated?
150mg/kg for both dogs and cats Carcass disposal recommend solutions suitable for euthanasia Proposed dosage schedule is Can be an irritant if given by this 2–3 x recommended dose for IV unless the animal administration when preparations containing concentrations of 390 Takes longer to take effect than via mg/ml of Pentobarbitone are used IV route: 1530 minutes (Sinclair, 2004: p 397.) Carcass disposal recommend 120–200 mg/kg as necessary (Bishop, 2005:p 291) Intracardiac (IC) 150mg/kg for both dogs and cats Can be painful if attempted in ful y Yes, this route of conscious animals administration is only suitable Carcass disposal recommend for unconscious, col apsed animals Dose for neonatal kittens and Takes longer to take effect than via puppies: despite discussion with animal welfare groups we have been unable to provide suitable Powdered preparation delivered in gelatine capsules can be hidden guidance on an acceptable dose for oral administration to neonates in food and is less likely to be at this time.
detected by dogs than mixing the liquid form with food.
Dose for sedation of dogs: 63mg/kg (Ramsay and Wetzel, 1998) Highly variable time to take effect even in dogs given the same dose.
Prolonged time to take effect: 30–90 minutes.
Effective dose is highly variable, dependent upon the animal's an overdose.
age, physical status and use of pre-euthanasia drugs Thiopentone Proprofol This method is time consuming and costly in comparison to other methods Carcass disposal recommend incineration Use of pre-euthanasia
drugs indicated?
Dogs and cats: 0.3ml/kg Slow, steady rate of injection iodine, tetracaine Commercial y available as a pre-prepared euthanasia solution accept in the USA Carcass disposal recommend incineration Intravenous (IV) One proposed dosage schedule Often available commercial y as is 100g of KCI dissolved in 1 litre a powder which is made into an after anaesthesia of water; 20–30ml of solution injectable solution by dissolving intracardiac (IC) sufficient for euthanasia of dogs weighing 15–20kg Carcass disposal recommend 12 mmol/kg of body weight wil cause cardiac arrest (Beaver et al., 2001) Intravenous (IV) Saturated solution of MgSO . One Often available commercial y as sulphate (MgSO ) proposed dosage schedule is: a powder, which is made into an after anaesthesia injectable solution by dissolving 83% solution of MgSO dissolved intracardiac (IC) in boiling water: Saturated solution becomes very Dosage varies little if given by IV or IC route of administration (Avariez and Caday, 1958).
Large volumes required to achieve euthanasia But highly variable dose for individuals; one suggested Carcass disposal – recommend published effective dose: 20–38 ml for a 15 kg dog (Avariez and Caday, 1958).
80mg/kg dose (Close et al., 1996) Saturated aqueous solution 1g/ml at a dose of 2.5–4.0 mg/kg (Carding, 1977) Only suitable for small animals or animals already anaesthetised for Delivered in a carrier gas (usual y oxygen) at the minimum alveolar concentration (MAC) Requires an anaesthetic chamber or can be delivered via breathing for surgery and, systems and masks applied to Human health hazard if inhaled are not permitted to regain Carcass disposal recommend ANNEX 2: Guidelines on the intravenous injection of
Pentobarbitone for the euthanasia of dogs and cats
and specialist capture and restraint equipment to prevent
The World Society for the Protection of Animals strongly handlers being bitten and to minimise human contact
recommends the use of Pentobarbitone (also sometimes with animal body fluids. To facilitate safe handling of
cal ed Pentobarbitone sodium or sodium pentobarbital); these animals, sufficient sedation (pages 13–14) should
a barbiturate specifical y formulated for euthanasia. be used prior to injection with the euthanasia agent.
The intravenous (IV) injection of Pentobarbitone 20% 5. Assessment of the animal's temperament
solution is regarded as the most humane method of euthanasia for dogs and cats. The method of and ease of handling
intravenous injection for dogs and cats can be mastered Animals that are not used to being handled by humans easily with training. In most cases animals show may experience fear when placed in novel surroundings, little or no resistance, provided that they are handled which may result in them showing defensive or avoidance considerately and that they are used to close human behaviour. Any animals that are likely to be fractious or contact. In certain countries euthanasia by intravenous difficult to handle may pose a risk to personnel through injection may only be performed by a veterinarian or by aggressive behaviour. In these instances it is both more operators working under veterinary supervision.
humane and safer for these animals to be sedated prior to euthanasia with sufficient time being al owed for the 1. Personnel
sedative to take maximum effect before euthanasia is Trained, competent and considerate personnel are essential for the humane handling of animals for euthanasia.
Some nervous and aggressive dogs may require muzzling to avoid danger to handlers. If no muzzle is available, A minimum of two people are required for intravenous a bandage tied around the dog's nose and then behind injection: one person should be able to restrain the the head (also known as a tape muzzle) can work in the animal safely and humanely (referred to hereafter as ‘the assistant'), while the second accurately delivers the intravenous injection for euthanasia (referred to Feral cats require special consideration as they are hereafter as the operator).
general y extremely fearful of humans. This presents both a welfare concern for the cat and a safety concern for the handlers, as the cat's defensive-aggressive Appropriate preparation must be made for smooth behaviour can inflict injury. The most satisfactory induction, and to ensure safe and humane handling of method of capturing a feral cat is to use a cat trap with a animals for euthanasia. In the first instance, personnel squeeze back facility (Figure 1). The captured cat is then should ensure that al materials are available to hand pressed against the mesh on the side of the cage so that and the environment is suitable, as fol ows.
an injection of a pre-euthanasia agent (pages 13–14) can be given. Once suitably sedated/immobilised the cat can 3. The environment
be handled safely. A quiet room away from other animals is required in 6. Materials
order to avoid dogs and cats becoming excited before the procedure, which would make them difficult to The fol owing materials are required for intravenous handle, requiring additional restraint.
An examination table approximately 90cm in height, with a non-slip surface, facilitates handling and al ows • Disposable syringes with eccentric (i.e. off-centre) for accurate injection.
• For cats, a syringe size of 2ml is recommended.
Good lighting of the area is essential to enable the • For dogs, syringe sizes of 5, 10 and 20ml wil be operator to see the site of the injection (usual y the suitable for most weights.
cephalic vein on the animal's foreleg); therefore facilitating precise delivery of the injection.
Disposable needles
• Needle diameter is measured by the ‘gauge': the
4. Special precautions should be taken for
larger the gauge the finer the needle.
suspect rabid animals
• Needles are usual y supplied in different coloured Extreme care should be taken when handling and
containers according to gauge for easy identification. euthanasing animals suspected of having rabies. Special
The size of the needle depends upon the size of the precautions include protective clothing for personnel,
animal and the substance to be injected. For an

Figure 1.
Figure 2.
Photograph of a squeeze-back cage for use with feral cats.
Photograph showing a dog restrained for intravenous injection. The assistant stands to left of the dog, and A – Front door to the cage. Once lifted open the cat can be enticed to enter from a cat trap
her right thumb is used to raise the cephalic vein to B – The external 'arms' are moved towards the assistant and the rear wal of the cage pushes the cat
enable the operator to insert the needle. Her left arm flat against the facing wall in the squeeze-back mechanism.
restrains the dog under the chin.
intravenous injection of Pentobarbitone the fol owing equal to the volume of liquid to be withdrawn. Fill the are recommended: Cats: needle of 22–24 gauge and syringe with the correct dose, calculated according to length 0.75 inches (2cm), Dogs: needle of 18–22 the manufacturer's instructions for the animal's weight. gauge and length 1 inch (2.5 cm) is convenient for Remove the needle and syringe from the bottle and most size of dog.
replace the cap on the needle for safety. (b) Handling and restraint
If permanent plastic cannulae are available for use they are preferable as they minimise the risk that the needle Gently lift the animal on to the examination table. The may slip during the procedure resulting in some or all of dog should be facing the operator who wil be giving the drug not being delivered directly into the vein (see the intravenous injection. Large or fractious dogs may section 7e). The technique for inserting a plastic cannula require more than one handler for restraint. If the is similar to that for giving an intravenous injection, but operator is right handed, the assistant should stand may take a little more training and practice; insertion is on the animals left. Where possible the animal should especial y difficult in smal er dogs and cats.
be in the sitting or lying position. The assistants' arm passes over the back of the and the other arm holds the animal under the chin (Figure 2). Injection of Pentobarbitone, 20% solution is considered as ‘best practice'; however some euthanasia products have been combined with a local anaesthetic agent The cat should be gently placed onto the examination or Phenytoin. The pharmacological differences are table, facing the operator for intravenous injection. The inconsequential but such compounds may be more assistant should hold the cat against their body, making easily obtained in some countries.
the cat feel secure. Dose rate
The animal's head should be held under its chin with Where possible the animal should be weighed. If this one of the assistant's hands, while the other hand is not possible, experienced personnel may be able to raises the cephalic vein (Figure 3). The cat's foreleg estimate the animal's weight with sufficient accuracy. should be pushed forward at the elbow, and the thumb The dose of Pentobarbitone should be determined and forefinger used to apply gentle tourniquet pressure, according to the manufacturer's instructions.
as described for dogs in Figure 4.
7. Method
(c) Site of injection
(a) Filling the syringe
The cephalic vein in the animal's foreleg is the most A new, disposable needle should be attached to the convenient site for intravenous injection. When the nozzle of a new, disposable syringe, and then inserted animal is held correctly the cephalic vein is visible into the bottle containing Pentobarbitone for fil ing. on top of the foreleg (Figure 4). Once the animal has To prevent a vacuum forming in the bottle, resulting been suitably restrained, it may be necessary to aid in difficulty with subsequent withdrawal of fluid, it is visualisation of the vein, particularly in cats and small advisable first to inject into the bottle an amount of air dogs, to clip a smal amount of hair on the foreleg where the injection is to be given.

(d) Preparation for the injection
The assistant's thumb and forefinger of the left hand
is used to create a tourniquet effect at the ‘crook' of
the elbow and inflate or ‘raise' the cephalic vein. Mild
pressure is applied: using the thumb with a slight
outward rotation the cephalic vein becomes clearly
visible for injection (Figure 4).
(e) Starting the injection
The cap is removed from the needle and the point
of the needle is gently inserted through the skin up
and into the vein. The needle is then slid up the
vein, paral el to the skin surface. Before injection of
Pentobarbitone, it is essential to confirm that the
Figure 3.
needle is correctly positioned in the vein. In large dogs Typical restraint of a cat for intravenous injection. The cat is held close to the blood wil flow natural y back into the liquid within the assistant's body, the animal's head is held under the chin with one hand and the syringe. In smal dogs and cats it may be necessary assistant uses their other hand to raise the cephalic vein.
to draw the plunger of the syringe back slightly: if positioned correctly blood should flow back into the syringe verifying the needle is indeed in the vein. After the operator has confirmed that the needle is correctly positioned, the assistant releases their thumb pressure so that the intravenous injection can be given.
(f) Ensuring the injection has been delivered
The calculated dose of the agent is injected with care
ensuring that the needle remains in the vein and that injection into the surrounding tissues is not occurring. Injection outside of the vein is rare but possible, and causes swel ing around the vein. Should this occur the procedure should be stopped, the syringe and needle Figure 4.
removed and a new attempt made at a different position Insertion of an intravenous cannula into the cephalic vein. The operator is right on the vein or using the vein on the other foreleg. handed. The assistant stands to the side of the dog, and uses their thumb to raise Extravascular injection of Pentobarbitone may cause the cephalic vein, enabling the operator to insert the needle. pain and irritation to animals and every effort should be A – Shaved area exposing the cephalic vein
taken to ensure precise delivery into the animal's vein.
B – Raised cephalic vein is clearly visible
C – 'Crook' of the elbow
D – The assistant's thumb and forefinger create a tourniquet effect. The thumb is
Normal y dogs and cats will become unconscious rotated outward slightly to raise the vein before the end of the injection and death fol ows almost immediately with complete freedom from pain the saphenous vein is considerably less convenient to or distress when using the recommended dose and use than the cephalic vein, as it is highly mobile when with a confident but gentle approach. Death should pressure is applied making accurate injection difficult. be confirmed using the indicators stated on page 5. Ideal y operators should check for the absence of the The technique for raising the saphenous vein is similar heartbeat using a stethoscope, listening to the left side to that used when injecting into the cephalic vein, of the chest where the beat is most audible in life or but it is more awkward for the assistant to achieve by checking for a pulse, by palpation over the medial as the animal has to be placed on its side (in lateral aspect of the animal's hind limb. If there's any doubt recumbency) and the hind leg is lifted. The assistants operators should wait for rigor mortis to set in before thumb is placed on the outside of the animal's hock disposing of the animal's carcass.
joint, while the forefinger encircles the inside of the joint. Thumb pressure is applied with a slight outward (g) Other sites for intravenous injection
rotation to raise the vein for injection. This technique If injection via the cephalic vein is not possible, other requires additional skil , and should only be attempted sites may be used for intravenous injection, but they by experienced personnel. may be more difficult and require greater skil . 8. Additional resources
The saphenous vein can be accessed in either of the Humane Society of the United States, Humane hind legs. It is easier to locate in larger dogs than in Euthanasia by Injection: Training Video Series. cats and smal dogs. The vein runs down the inside Produced by the Humane Society University, of the hind leg from the animal's body, until it crosses to the outside of the leg above the hock, where it is easiest to reach for intravenous injection. However



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