Mechanical methods - Penetrative captive-bolt followed by pithing

Captive-bolt devices work in a similar way to firearms, although unlike free-bullet firearms, the bolt remains captive within the barrel. This bolt strikes the animal’s head (percussion) which causes concussion. When used successfully with ruminants and pigs, the impact of the bolt on the skull renders the animal immediately unconscious. A penetrative captive-bolt stunner also fires a retractable bolt into the animal’s head allowing the bolt to penetrate the cortex and mid-brain of the animal. The bolt is projected either by compressed air or a blank cartridge. Following the administration of a successful captive-bolt stun the animal will collapse immediately, rhythmic breathing will cease and the corneal reflex will also be lost (a corneal reflex can be elicited by touching the cornea of the open eye with the fingertip - in a conscious animal the eyelid will close). The response to a painful stimulus (e.g. a nose-prick with a hypodermic needle) will be absent.  These symptoms are accompanied by the onset of tonic seizures lasting several seconds. The clonic phase follows the tonic phase and can be recognized by the presence of kicking or paddling movements which generally last between about 15 and 45 seconds. There is likely to be some bleeding from the hole in the skull made by the bolt and from the nose of the animal. Physical damage to the brain caused by the penetration of the bolt may not necessarily result in death and so pithing must be performed as soon as possible to ensure the death of the animal. Pithing involves inserting a flexible wire or polypropylene rod through the hole in the head made by a penetrative captive-bolt. The movement of the rod destroys the brainstem and upper spinal cord, ensuring death, and reduces the reflex kicking which can occur after stunning. In the case of an on-farm kill for disease control, other implements such as screwdrivers may also be utilised to perform this function. The rod is then thrust towards the tail through the brain to the level of the brainstem and, if it is long enough, into the spinal cord. It is then slid back and forth to cause maximum damage to the brain and upper spinal cord, a practice known as ‘fiddling’ or `rodding’. Initially the animal will show violent muscle contraction, but then reflex muscle movement is inhibited. Disposable pithing canes, which remain in the carcase, are available. Whilst both these procedures are humane when carried out correctly, they may be distressing to watch and they require a competent and confident operator. For more information on pithing see http://www.hsa.org.uk/bleeding-and-pithing/bleeding

Animals should be closely monitored following stunning to ensure the absence of brainstem reflexes. If there is any doubt regarding the efficacy of the shot, the captive-bolt should be applied again. The correct positioning of these shots is described in the HSA online guide for Captive-bolt Stunning of Livestock. Should there be any doubt in the mind of the operator as to the correct target area for firearms or captive-bolt equipment, then it should be identified and, if possible, marked. This can be done using a spray marker, a felt pen, or in the case of a very dark-coated animal, French chalk. For the application of the captive-bolt stunner the animals should be restrained. The aim should be to position the animal so it can be shot accurately and will be easily accessible for pithing immediately after collapse. Animals can be confined within a small pen or behind a movable gate. Alternatively, the animal can be held with a halter. Individual pigs can be restrained by passing a rope noose around the upper jaw, behind the canine teeth: when the pig pulls back it will be in a position to be immediately stunned.

The bolt velocity and length of bolt should be appropriate to the species and type of animal and in accordance with the recommendation of the manufacturer. See the HSA online guide to Emergency Slaughter and Captive-bolt Stunning of Livestock for more detailed information on the use of captive-bolt equipment. Information is available on the types of equipment available, the correct positioning for different species and the maintenance procedures and safety considerations for captive-bolt equipment. When used for killing for disease control, more than one stunner may be necessary to prevent overheating.  Furthermore, a back-up device should always be available.

Positioning

Positioning of the captive-bolt for cattle, pigs and deer is the same as listed previously in the free-bullet firearm section (Figures 5, 6 and 8 in mechanical method section). However, the correct position for stunning sheep is different. For these animals it depends on whether the animal is polled (hornless) or horned. For polled sheep, the muzzle of the stunner should be placed on the highest point of the head, on the mid-line and aiming straight down (Figure 9a). For horned sheep, the muzzle of the stunner should be placed on the mid-line, behind the ridge between the horns and aimed towards the base of the tongue (Figure 9b).

Following stunning with a penetrative captive-bolt, pithing must be performed without delay to prevent the possibility of the animal recovering from the stun. Specifically, when horned sheep and goats are shot in the poll position they must be pithed within 15s.

Figure 9a: The optimum position for using a captive-bolt on hornless sheep.

Figure 9b: The optimum position for using a captive-bolt on heavily horned sheep and all goats.

Considerations when using captive-bolt stunning and pithing for depopulation due to disease control

Captive-bolt stunning followed by pithing can be used for on-farm killing of animals where a free-bullet is impractical, although certification may be necessary for the use of this method.  When using a captive-bolt device it is vital that it receives regular cleaning and maintenance (see Captive-bolt Stunning of Livestock and TN4-safety-maintenance-captive-bolt-HSA.pdf for details). At least one spare captive-bolt device should be available and the use of devices rotated to prevent overheating. Ensuring the correct positioning of the bolt is essential as misfiring may seriously compromise animal welfare.

The use of captive-bolt devices followed by pithing has advantages for use during on-farm depopulation. The mobility of this equipment reduces the need to move animals, which is beneficial for the welfare of the animals and also the prevention of the spreading of disease. A further benefit to animal welfare is the immediate onset of unconsciousness which is sustained throughout the killing process.

There are, however, disadvantages to this method. The animals have to be restrained and for animals which are not habituated to human contact, this may cause fear and distress. Misplaced shots may be a particular problem if the animals are not adequately restraint and/or become agitated as they may not remain still. The safety of the personnel performing the pithing or bleeding may be jeopardised by the animals’ post-stun convulsions. As with the use of firearms the destruction of brain tissue may prevent the diagnosis of some diseases and the leakage of body fluids may pose a biosecurity risk.

If the animal was shot using a firearm, or stunned using a captive-bolt, but there is doubt surrounding the efficacy of the stun/kill the procedure should be performed again immediately. If the first attempt was off-target the second shot should be performed in the correct position. If the first shot was in the correct position but ineffective the second should be above and to one side of the normal target position.

Conclusion – species and situations

Free-bullet firearms and captive-bolt stunning, followed by pithing, are methods suitable for killing pigs (up to six months of age), cattle, sheep, goats and deer. Due to the skull structure of adult pigs, problems may arise when using a captive-bolt and it is recommended that, where possible, they are destroyed by a free-bullet humane killer or a shotgun, or stunned and killed using electricity (see Electrical Killing section below).

For adult cattle, it may be advisable to sedate them prior to stunning with a captive-bolt. This can be done by administering a sedative while they are in a race or crush and then allowing them to settle in a pen or shed. When the sedative has relaxed and immobilised the animals, stunning and pithing can be performed by a killing team. Sedating adult cattle enhances safety of personnel and potentially reduces the stress experienced by the animals.

Next: Killing mammals using electricity