A captive bolt pistol (also variously known as a cattle gun, stunbolt gun, bolt gun, or stunner) is a device used for stunning beasts prior to slaughter. Proper stunning is essential to prevent the pain and suffering of the beast during the bleeding (exsanguination) process (which is itself necessary to prevent meat spoilage) during butchering. The principle behind captive bolt stunning is a forceful strike on the forehead using a bolt to induce unconsciousness. The bolt may or may not destroy part of the brain.
The bolt is a heavy rod made of non-rusting alloys, such as stainless steel. It is held in position inside the barrel of the stunner by means of rubber washers. The bolt is usually not visible in a stunner in good condition. The bolt is actuated by a trigger pull and is propelled forward by compressed air or by the discharge of a blank round ignited by a firing pin. After striking a shallow but forceful blow on (or through) the forehead of the beast, spring tension causes the bolt to recoil back into the barrel.
Variations
The captive bolt pistols are of three types: penetrating, non-penetrating, and free bolt.
In the penetrating type, the stunner uses a pointed bolt which is propelled by pressurized air or a blank cartridge. The bolt penetrates the skull of the beast, enters the cranium, and catastrophically damages the cerebrum and part of the cerebellum. Due to concussion, destruction of vital centres of brain and an increase in intracranial pressure, the beast loses consciousness. This method is currently the most effective and widely used type of stunning, since it physically destroys brain matter (increasing the probability of a successful stun), while also leaving the brain stem intact (thus ensuring the heart continues to beat, facilitating a successful bleed). One disadvantage of this method is that brain matter is allowed into the blood stream, possibly contaminating other tissue with bovine spongiform encephalopathy (B.S.E.).
The action of a non-penetrating stunner is similar, but the bolt is blunt with a mushroom-shaped tip. The bolt strikes the forehead with great force and immediately retracts. This concussion is responsible for the unconsciousness of the animal. This type of stunner is less reliable at causing immediate and permanent unconsciousness than penetrating types; however, it has undergone a resurgence of popularity due to concerns about mad cow disease. In the European Union, this captive bolt design is required for slaughter of animals that will be used for pharmaceutical manufacture.
The free bolt stunner is used for the emergency in-the-field euthanasia of large farm-beasts who cannot be restrained. It differs from a true captive bolt gun in that the projectile is not retractable; it is similar in operation to a powder-actuated nail gun or conventional firearm. Capable of firing only when pressed firmly against a surface (typically the beast's forehead), the device fires a small projectile through the beast's skull. The veterinarian can then either leave the beast to expire from the projectile wound, or administer lethal drugs.
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