Veterinary Handbook Contents

9.4 Methods For Euthanasia

9.4.1 Use Of Firearms

9.4.1.1 Licencing And Safety

A current firearms licence must be held by the operator and the firearm must be registered. Lock the firearm away when not in use and secure the ammunition in a separate location.

Always treat a firearm as if it is cocked and loaded. Never point it at yourself or another person and do not leave it unattended. Before shooting, look down the line of fire and check where an exiting bullet might travel. Concrete and steel yards carry the risk of ricochet. Soft ground or hay bales in the background are recommended.

Do not shoot at point blank range. Unlike captive bolts, the end of the barrel of a firearm must not be pressed against the skull because of the dangers of blowback which may damage the firearm or injure the operator. A distance of 10 - 100 cm from the end of the barrel to the skull is recommended. Appropriate restraint is important and the head must be still before firing. Standing animals may be restrained in a crush or with a halter. Animals may be sedated with xylazine so that they are lying down before the procedure is completed.

9.4.1.2 Effective Use

The recommended minimum calibre of ammunition is .22 long rifle. Soft nose or hollow point bullets are preferred over solid bullets because they fragment inside the skull. This ensures maximal damage and means that bullets are less likely to exit the skull.

The recommended points of entry and direction of bullets are the same as for a captive bolt (Figure 9.1). Firearms should not be directed at body sites other than the brain.

9.4.2 Use Of Penetrating Captive Bolt

Penetrating captive bolt guns are also known as slaughter pistols, stunners and humane killers. They are designed to drive a retractable bolt into the brain. This usually causes unconsciousness and most of the time, but not always, causes death. The muzzle of the captive bolt must be pressed against the head of the animal. Standing animals should be restrained with a halter or in a crush. Alternatively, animals may be sedated with xylazine so that they are lying down when euthanised.

Non-penetrating captive bolts are available but are not recommended because they are less effective. They have a mushroom-shaped head and are designed to deliver a non-penetrating blow to the forehead, causing concussion and loss of consciousness. They must always be followed up by bleeding.

Penetrating captive bolts are safer than firearms in that there is no ricochet and no over penetration. However, they are still very dangerous in untrained hands. Always treat them as loaded. Never point at yourself or another person. Never leave unattended.

In all Australian states and territories, except Western Australia and Tasmania, the operator does not require a firearms licence to own or use a captive bolt and registration of the captive bolt gun is also not required.

The target for a captive bolt gun is the same as for a rifle. It must not be directed at a body site other than the brain. Frontal or poll shots can be used. For the frontal shot, the bolt should penetrate the forehead in the midline on a line between the inside corner of the eye and the base of the horn (Figure 9.1). The shot should be directed down the middle of the neck. For the poll shot, the bolt should penetrate the back of the head in the middle of a line drawn between the base of the horns while aiming at the base of the tongue.

The temporal position, where the shot is into the side of the head, is not recommended for captive bolts or firearms. The greater depth of tissue and layers of bone between skin and brain in this site mean that captive bolts and most lower calibre firearms will not reliably penetrate the brain.

If there is any doubt that the animal has not been killed, then it should be shot again, concentrating on the correct position and angle of the shot. Alternatively, it should be bled or pithed if the shot has rendered the animal unconscious. It is important that a knife or pith is always at hand to execute these follow-up methods if necessary.

Figure 9.1: Target for frontal and poll shots with a captive bolt or firearm

Blank cartridges are colour coded according to the amount of charge. Follow the manufacturers’ recommendations for the correct charge to use for different types of animals. Generally for calves, sheep and goats, the lowest power charges are adequate. Using more powerful charges may result in excessive wear of the weapon.

Correct cleaning and maintenance according to manufacturers’ instructions are essential to prevent build-up of carbon and related corrosion. If not maintained properly, there is a risk of misfires and improper projection of the bolt and reduced effectiveness of the procedure.

9.4.2.1 Pithing Following The Use Of A Captive Bolt

Pithing is the process of destroying brain tissue in and around the brainstem to ensure death.

It is a follow-up method of killing animals after a penetrating captive bolt has been used to render the animal unconscious. The method may sometimes stimulate a transient reaction even if the animal is dead.

A curved steel rod or a long screw driver can be used as a pith. Pass the pith through the hole in the front of the skull made by the penetrating captive bolt (Figure 9.2). It is initially inserted as if to pass down the spinal column of the neck. When it strikes bone at the bottom rear of the brain cavity withdraw it slightly and with a stirring action macerate the brain, especially the brainstem toward the bottom rear of the skull. Take care to avoid being hurt by any movement of the limbs.

Figure 9.2: Pithing involves inserting a pithing device through the hole made by a captive bolt and disrupting the brain tissue.

9.4.3 Use Of Blunt Trauma

Blunt trauma is only permitted on calves, lambs or kids up to 24 hours old.

Use a suitable solid heavy object such as a mash hammer, stone hammer, back of an axe, steel pipe or steel bar. A short handled 1.2 kg hammer with 4 x 4 cm striking face is recommended.
It is advisable to use the same solid heavy object each time to give consistent results. Using different blunt instruments that have different shapes and weights may cause undesirable variation in results.
Deliver a single sharp blow sufficient to crush (cave-in) the skull. Target the forehead (frontal position) in the same location that a firearm or penetrating captive bolt would target and aim the strike down a line through the cervical vertebrae (neck). The target is the intersection of line between inside the corner of eye and base of the horn (or where the horn would be in polled animals which is slightly above the ear).

In some publications the recommended target is the crown of the head. This is usually adequate in newborns because the skull bones are relatively soft. However, the frontal position is preferable because the bone is less thick over the brain in that area and the blow is naturally directed at the brainstem.

If the animal does not become immediately unconscious, strike again more forcefully, concentrating on hitting in the correct location and direction. A follow-up method, such as bleeding or pithing, is recommended but is not required if the animal is confirmed dead (use the five finger head check). Training and skill is essential for this method so practise on dead animals.

9.4.4 Use Of Bleeding

Bleeding is also known as bleeding-out or exsanguination. It is achieved by severing major blood vessels with a knife. The most suitable major vessels to be severed are those of the neck, chest or armpit. The procedures are known respectively as the throat cut, armpit cut and chest stick. It is sometimes performed in preparation for necropsy. Exsanguination may make assessment of tissues easier at necropsy by preventing free blood from pooling in cavities.

In sheep and goats, the throat cut may be used as the primary method of euthanasia if a captive bolt or firearm is unavailable. This is severing the carotid arteries with a throat cut completely interrupting the supply of arterial blood to the brain. Pre-injection with xylazine is recommended if available.

The throat cut should not be used as a primary method of killing cattle. In cattle, bleeding is a follow-up procedure, only to be used on unconscious animals after a firearm, captive bolt or blunt trauma have been used. This is because cattle have two different sources of arterial blood supply to the brain: the carotid arteries and the vertebral arteries. The vertebral arteries are enclosed in the spinal canal at the anterior neck and are not severed when the throat is cut.

All three cuts may be used in unconscious animals as a follow-up method to gunshot, captive bolt or blunt trauma.

Site preparation and management is important when bleeding is used in euthanasia. Heavy blood loss may occur for up to two minutes. Care must be taken to ask bystanders to leave and it should not be performed in public view. A well drained area is required to wash away blood.

The knife should have a stiff 15 cm (6-inch) length blade with a non slip handle and finger guard. Boning knives are ideal. It must be sharp. Carry a steel or sharpening stone if multiple animals are to be bled.

The chest stick aims to sever the major vessels extending from the top of the heart, such as the aorta and vena cava. As a follow-up method, it is the preferred method of the three bleeding cuts because all blood flow to the head is stopped immediately once the vessels are cut. The lungs collapse and skin damage is minimal if that is to be salvaged. However, the chest stick can make pathological changes in the chest difficult to assess at necropsy.

Figure 9.3: Diagram showing a chest stick with the knife inserted into the thoracic inlet in the midline of the ventral neck between the first ribs and above the sternum

The heart sits in the bottom-front part of the chest with major vessels extending from top of the heart (Figure 9.3). These vessels are within easy reach of a 15 cm blade inserted into the chest in the midline where the brisket joins the ventral neck. Once the blade is deep inside the chest, a sideways slicing action in one direction and then the other, ensures that the vessels are severed.

The throat cut aims to sever the carotid arteries at the level of the throat, near where the neck joins the head. It may make pathological changes in this area difficult to assess at necropsy. The best method for performing the throat cut is by fully inserting the knife just behind the angle of the jaw beneath the neck bones (Figure 9.4). A knife such as a boning knife with strong, sharp 15 cm blade, a pointed tip and a non-slip handle is essential. This method causes the carotid arteries to be cut during insertion of the knife. An outward cut (directed ventrally) ensures the carotid arteries and jugular veins are severed and also the windpipe.

Other knives may be used but if the knife does not have a sharp point, it will require cutting from the skin inward. Make an inward cut through the skin with the neck extended over the joint connecting the skull with the first neck bone (the atlanto-occipital joint). The skin, windpipe and major blood vessels are each severed in rapid succession. The obvious shortcoming is that the vessels (and hence the blood supply to the brain) are the last tissues to be cut.

Figure 9.4: The throat cut with a knife inserted at the angle of the jaw and cutting outwards to sever the carotid arteries, jugular veins and windpipe

The armpit cut aims to sever the vessels under the arm. It is the preferred method if you wish to avoid damage to throat and chest structures caused by the other methods. Lift the leg and insert the knife deep into the axilla, severing the large blood vessels (Figure 9.5). The armpit cut should only be used as a follow-up method to a firearm, captive bolt or blunt trauma, and only if the animal is unconscious. A knackery service may refuse to remove the carcase because of the damage to the skin.

Figure 9.5: The armpit cut. The front leg is raised and a knife inserted into the armpit and the brachial artery and vein severed

9.4.5 Use Of Anaesthetic Overdose

If the brain is to be sampled at necropsy then an overdose of anaesthetic is recommended. An overdose of barbiturate anaesthetic is commonly used. The carcase must be burned or buried immediately after the necropsy to avoid poisoning animals that might eat parts of the carcase. A knackery or rendering service may refuse to remove it.

An alternative approach is to administer a maximal dose of xylazine sufficient to anaesthetise the animal. When the animal is unconscious, a saturated solution of magnesium sulphate (also known as epsom salts and one of the first large animal anaesthetics) is injected intravenously to kill the animal. The dose rate of a saturated magnesium sulphate solution required to kill an animal is 2 mL/kg bodyweight administered intravenously. The 1 L required to kill a steer could be administered via a flutter valve fixed to a bottle and a 14 to 16g needle. The 100 mL required to kill an adult wether could be administered via two 50 mL syringes with an 18g needle. Prior anaesthesia with xylazine is always necessary, except when the animal is already moribund.

The advantage of the xylazine/magnesium sulphate method is that it is cheap and renders the carcase distasteful. Scavengers, if they should eat the carcase, would be unaffected other than perhaps by temporary vomiting and diarrhoea.

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