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A working knowledge and experience of different euthanasia techniques is useful

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Euthanasia of horses alternatives to the bullet

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Derek Knottenbelt qualified from Edinburgh in 1970 and after two years in Zimbabwe in government service returned to the UK to private practice, eventually becoming a partner in a mixed practice. After 12 years, he turned to an academic career as lecturer and senior lecturer at the Faculty of Veterinary Science, University of Zimbabwe. Since 1989, he has been lecturer in equine medicine at the University of Liverpool. He was awarded a doctorate of veterinary medicine and surgery by the University of Edinburgh in 1990.

DEREK KNOTTENBELT

EUTHANASIA of horses is probably one of the most demanding procedures a veterinary surgeon is likely to face. There are emotive issues involved which make it akin to the euthanasia of small animals and logistics which make it akin to the euthanasia of farm animals. The safety of personnel in the vicinity is paramount and adequate restraint and facilities are vitally important. Notwithstanding these requisites, veterinary surgeons are bound to find themselves in the position of having to compromise and a working knowledge and experience of different techniques is, therefore, useful. The disposal of carcases is also an important consideration but it should in no way be allowed to take precedence over the welfare of the animal or the skill of the operator. If euthanasia is elective, then arrangements should be made in advance (with a knacker, hunt kennels, etc) for immediate carcase disposal.

THE ALTERNATIVES Death is said to have occurred when all reflex activity has ceased and both respiration and heart function have stopped (the heart may beat for up to 20 minutes following shooting). In considering alternatives to the use of a free bullet firearm, it is important to realise that this method does have obvious advantages when used by experienced veterinary surgeons (ie, speed, carcase disposal and cost). The major disadvantages are also obvious (danger to personnel, the requirement for experience and a firearms licence). Moreover, it is aesthetically displeasing to the public, although most recognise it as the accepted method. Three alternative techniques are discussed below pentobarbitone injection (with or without a premed-

Death 0 should be quiet and instantaneous with-

Out yPremonition * Th agent should be safe for the operator and th plik * The agent should be easily handled and stored *ITheagent should be convenient to administer * There should he no problem with carcase utilisation 462

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an emergercy situation, the site chosen for euthanasia is oftn predetermined. Elective

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euthanasia, however, sihould only be pe.fomed after carefully assessing the environment to ensure safety and efficiec. The eas of access for the knacker wagon shol possibili

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ficulties. Euthanasia alongsie fa ipre in a is fraught Wth 0d can also be-very dangerous for all partie.

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icant), thiopentone sodium injection with pentobarbitone (with or without a premedicant muscle relaxant and/or sedative), and quinalbarbitone sodium and cinchocaine hydrochloride injection (with or without a premedicant). It should be noted that severance of the aorta per rectum, although often reported, is a very difficult procedure. It is not without danger to the veterinary surgeon, nor is it painless for the horse. Furthermore, death is slower and more violent than is commonly reported. This technique should, therefore, not be undertaken lightly.

PENTOBARBITONE INJECTION Prerequisites * A suitable volume (calculated at 1 ml/3 kg bodyweight) of 200 mg/ml pentobarbitone sodium preloaded into the minimum number of syringes.

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* A suitable premedicant, preferably an alpha2-agonist at full sedative dose. * A preplaced 14 gauge (G) jugular catheter. * Suitable restraint and choice of environment (see box, below left). Method The horse is restrained and the jugular catheter placed. The premedicant is administered by slow intravenous injection via the catheter and time is allowed for it to exert its maximal effect. The pentobarbitone is then administered as fast as possible; it should be noted that large syringes are better but may be difficult to handle. The horse will collapse after 30 to 40 seconds (longer if premedicated), with death occurring within three minutes of collapse. Some gasping and muscular activity may occur and collapse may be violent unless the horse is premedicated.

THIOPENTONE SODIUM INJECTION WITH PENTOBARBITONE Prerequisites * Separate preloaded syringes containing 0.1 mg/kg succinylcholine and 10 g thiopentone sodium. * A suitable volume (calculated at 1 ml/5 kg bodyweight) of 200 mg/ml pentobarbitone sodium preloaded in the minimum number of syringes. * A suitable premedicant, preferably an alpha2-agonist, at full sedative dose. * A preplaced 14G jugular catheter. (Note this method is unsuitable for 'off the needle' euthanasia.) * Suitable restraint and choice of environment.

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Advantages

Disadvantages

Quick and readily available

Collapse is violent with agonal gasping unless the horse is heavily premedicated

Cheap Non-irritant if accidentally injected

extravascularly No implications under the Misuse of Drugs Regulations 1985; commercial euthanasia solutions are scheduled so as to preclude the recording of individual usages

Prerequisites * A suitable volume (calculated at 1 ml/15 kg bodyweight) of 400 mg/ml quinalbarbitone sodium with 25 mg/ml cinchocaine hydrochloride (Somulose; Amolds) preloaded into a single syringe. A dose of 25 ml for horses under 145 cm (14.2 hands) in height and 50 ml for larger horses has been recommended (Knottenbelt and others 1994). * A suitable premedicant, such as an alpha2-agonist, at full sedative dose. Xylazine should not be used as a sedative prior to the administration of a quinalbarbitone and cinchocaine combination as excitement may be induced and death delayed. InPractice

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Volume of drug required makes multiple syringes essential which may be difficult to handle quickly enough Carcase disposal is expensive

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Advantages

Disadvantages

Quick

Collapse is violent unless the horse is heavily premedicated, particularly so in excited horses

Easily understood method with similarities to anaesthetic induction No implications under the Misuse of Drugs Regulations 1985, as the drugs are suitably scheduled for use in practice without the need to record individual usages

Complicated procedure involving numerous syringes and injections The volume of drug required makes multiple syringes essential which are difficult to handle quickly enough Muscular spasms and trembling may be aesthetically displeasing Carcase disposal is expensive

* A preplaced 14G jugular catheter. * Suitable restraint and choice of environment.

Method The horse is restrained and the jugular catheter placed. The selected premedicant is administered by slow intravenous injection and time is allowed for it to exert its maximal effect. The full dose of the quinalbarbitone sodium and cinchocaine hydrochloride mixture is then administered over 12 to 15 seconds. The horse is restrained by keeping its head down and allowed to collapse gently. Collapse can be expected about 30 to 40 seconds after the start of the injection; if a premedicant is used it will be delayed to 40 to 50 seconds. There may be an occasional gasp for up to two minutes after collapse and death usually occurs within three minutes of collapse.

Method The horse is restrained and the catheter placed. The premedicant, if required, is administered by slow intravenous injection via the catheter and time is allowed for it to exert its maximal effect. The thiopentone is then administered as a bolus as fast as possible, followed immediately by succinylcholine via the catheter. Collapse can be expected to occur about 30 to 40 seconds later, although it may occur after 20 to 30 seconds if no premedicant is used. The pentobarbitone is then administered as quickly as possible (again, large syringes are preferable but may be difficult to handle). The animal will exhibit muscular fasciculations andil 1S1 trembling with prolapse of the third eyelid. Death usualAdvantages ly occurs within three minutes of collapse.

QUINALBARBITONE SODIUM AND CINCHOCAINE HYDROCHLORIDE INJECTION

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Disadvantages

Quick

Premedication with xylazine is contraindicated

Wide dose range makes accurate dosage unnecessary

Solution is viscous making the required speed of injection potentially difficult to control (a catheter of minimum 14G should be used)

Relatively cheap Carcase disposal complications (expensive)

Single injection syringe contains the total volume of the drug combination Non-irritant if accidentally injected

extravascularly Collapse predictable even in excited/ exhausted horses

Drug combination is classified as schedule 2 under the Misuse of Drugs Regulations 1985, requiring that acquisitions/usages be recorded in a register Too rapid an injection causes an unacceptably

violent and prolonged period to death (horse effectively dies of heart failure) Slow injections induce 'normal' collapse but a prolonged death (horse is effectively anaesthetised) Occasional mild muscular trembling in upper forelimb and gasping

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CHOICE OF METHOD

The author recommends the use of quinalbarbitone and cinchocaine as an alternative to the free bullet firearm for euthanasing horses. The method is safe and convenient and is least likely to be associated with complications and aesthetically unacceptable effects. It is nonetheless very important to counsel all attendants carefully as to the possible untoward effects before the procedure is performed. Carcase disposal considerations should not be the primary concern of the veterinary surgeon called upon to perform euthanasia. His or her responsibilities are first and foremost the welfare of the animal and the safety of the attendants. Reference KNOTTENBELT, D. C., JONES, R. S., BRAZIL, T. J., PROUDMAN, C. J., EDWARDS, S. R. & HARRISON, L. J. (1994) Humane destruction of horses with a mixture of quinalbarbitone and

cinchocaine. Veterinary Record 134, 319-324 Further reading AMERICAN VETERINARY MEDICAL ASSOCIATION PANEL ON EUTHANASIA (1986) Journal

of the American Veterinary Medical Association 188, 252-

268

As a Veterinary surgeon you have special requirements for your personal financial planning.

JONES, R. 5. (1993) Euthanasia of horses. Equine Veterinary Education 4, 154-157 JONES, R. S. (1993) Euthanasia in

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horses. RCVS Newsletter, February. London, Royal College of Veterinary Surgeons

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Euthanasia of horses - alternatives to the bullet Derek Knottenbelt In Practice 1995 17: 462-464

doi: 10.1136/inpract.17.10.462

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alternative to the bullet