Stunning and Killing

Last updated 13 October 2017

Most animals slaughtered for food in Australia have their throats cut open with a knife (referred to as “sticking”) so that they can be bled out. Prior to this, they are typically meant to be unconscious (though as of 2011, 15+ abattoirs in Australia have permission from state governments to slit the throats of fully conscious animals, as part of the religious practices of “halal” and “kosher” slaughter). There are three main methods of ‘stunning’ intended to make animals unconscious before slaughter: captive bolt, electric, and gas chambers.

Due to the large numbers of animals being killed daily at slaughterhouses, it is impossible for painless stunning and killing to be achieved on all animals. Slaughterhouse workers (and covert video footage) often tell of animals who are “stuck” and bled out while fully conscious, or killed in other ways before being “stuck” (beaten with an iron bar or other blunt instrument, or having their neck broken). Pigs who are not correctly stunned, and who have not yet passed out or died from blood loss, end up drowning in the scalding tank.

Captive bolt stunning

Also called “percussion stunning”, this method produces a physical shock to the brain. The captive bolt, if used correctly, causes irreversible damage to the animal’s brain, and can be used on cattle, pigs, sheep and goats as well as horses and camels, although electrical stunning is more common for pigs and sheep. The captive bolt method of stunning is used throughout the world, and due to the minimal running costs is the preferred method in many developing countries.

There are two main varieties of captive bolt gun: penetrating and non-penetrating.

A penetrating captive bolt gun fires a blank cartridge, propelling a short bolt (metal rod) from the barrel through the skull bone and producing concussion by damaging the brain or increasing intracranial pressure, causing bruising of the brain. Some types of penetrating captive bolt guns have a handle and a trigger, while others have a hand-held barrel which, when tapped against the skull of the animal, sets off the cartridge explosion.

A non-penetrating captive bolt gun features a blunt bolt with a mushroom-shaped tip, which strikes the forehead of the animal with great force and immediately retracts, causing concussion and rendering the animal unconscious.

Electrical stunning

Electric stunning renders the animal unconscious by passing an electric current through the animal's brain. It is the usual method of stunning for pigs, sheep, goats, and poultry.

For pigs, sheep and goats, a low voltage alternating electric current is applied by means of two electrodes, which are placed on either side of the brain (or underneath the jaw and on the back of the neck) using tongs.

For poultry, an electrified water bath is used. Birds are shackled upside-down by their feet and dragged through a trough of water that is charged with a low voltage current. Birds that lift their heads (or are smaller than normal) manage to avoid the bath and go on to be painfully killed without stunning.

Because electric stunning does not usually cause damage to the brain, animals will regain consciousness if not quickly killed and bled out.

Gas chambers

Also called “controlled atmosphere stunning” or “controlled atmosphere killing”, this method involves placing animals into a container or chamber which lacks oxygen and contains an asphyxiant gas (one or more of carbon dioxide (CO2), argon or nitrogen), causing the animals to lose consciousness and, if left in the chamber long enough, to die.

The vast majority of pigs killed for food in Australia are stunned in carbon dioxide (CO2) gas chambers. While there are different models of chamber used, the more common variety is roughly 7-10m deep; the gas, being heavier than oxygen, sits below the level of the entrance. Inside this type of chamber, there are 5 or so steel cages known as gondolas. Pigs are forced by use of an electric prodder into the gondola (3 at a time for 5-6 month old “growers”, or 1 sow), which is then lowered into the gas. Hidden camera footage inside these chambers (Corowa slaughterhouse NSW, Big River Pork slaughterhouse SA) shows that the pigs suffer immensely, screaming and thrashing for air and trying desperately to escape as the gas suffocates them. The gondola eventually comes up the other side of the chamber and tips the unconscious pigs out onto a bench where they are shackled before having their throats cut open.

It is becoming increasingly common for poultry slaughterhouses to use gas chambers for stunning and killing, rather than the traditional method of electric stunning.