Animal slaughter

Animal slaughter is the killing of animals, usually referring to killing domestic livestock. It is estimated that each year, 80 billion land animals are slaughtered for food. Most animals are slaughtered for food; however, they may also be slaughtered for other reasons such as for harvesting of pelts, being diseased and unsuitable for consumption, or being surplus for maintaining a breeding stock. Slaughter typically involves some initial cutting, opening the major body cavities to remove the entrails and offal but usually leaving the carcass in one piece. Such dressing can be done by hunters in the field or in a slaughterhouse. Later, the carcass is usually butchered into smaller cuts.
The animals most commonly slaughtered for food are cattle and water buffalo, sheep, goats, pigs, deer, horses, rabbits, poultry, insects, and increasingly, fish in the aquaculture industry. In 2020, Faunalytics reported that the countries with the largest number of slaughtered cows and chickens are China, the United States, and Brazil. Concerning pigs, they are slaughtered by far the most in China, followed by the United States, Germany, Spain, Vietnam, and Brazil. For sheep, again China slaughtered the most, this time followed by Australia and New Zealand. Similarly, the amount of fish used for production is highest in China, Indonesia, Peru, India, Russia, and the United States.

Modern history

The use of a sharpened blade for the slaughtering of livestock has been practised throughout history. Prior to the development of electric stunning equipment, some species were killed by simply striking them with a blunt instrument, sometimes followed by exsanguination with a knife.
The belief that this was unnecessarily cruel and painful to the animal eventually led to the adoption of specific stunning and slaughter methods in many countries. One of the first campaigners on the matter was the eminent physician, Benjamin Ward Richardson, who spent many years of his later working life developing more humane methods of slaughter as a result of attempting to discover and adapt substances capable of producing general or local anaesthesia to relieve pain in people. As early as 1853, he designed a chamber that could kill animals by gassing them. He also founded the Model Abattoir Society in 1882 to investigate and campaign for humane methods of slaughter and experimented with the use of electric current at the Royal Polytechnic Institution.
The development of stunning technologies occurred largely in the first half of the twentieth century. In 1911, the Council of Justice to Animals was established in England to improve the slaughter of livestock. In the early 1920s, the HSA introduced and demonstrated a mechanical stunner, which led to the adoption of humane stunning by many local authorities.
The HSA went on to play a key role in the passage of the Slaughter of Animals Act 1933. This made the mechanical stunning of cows and electrical stunning of pigs compulsory, with the exception of Jewish and Muslim meat. Modern methods, such as the captive bolt pistol and electric tongs were required, and the act's wording specifically outlawed the poleaxe. The period was marked by the development of various innovations in slaughterhouse technologies, not all of them particularly long-lasting.

Methods

Stunning

Various methods are used to kill or render an animal unconscious during animal slaughter.
;Electrical : This method is used for swine, sheep, calves, cattle, and goats. Current is applied either across the brain or the heart to render the animal unconscious before being killed. In industrial slaughterhouses, chickens are killed prior to scalding by being passed through an electrified water-bath while shackled.
;Gaseous : This method can be used for sheep, calves and swine. The animal is asphyxiated by the use of CO₂ gas before being killed. In several countries, CO₂ stunning is mainly used on pigs. A number of pigs enter a chamber which is then sealed and filled with 80% to 90% CO₂ in air. The pigs lose consciousness within 13 to 30 seconds. Older research produced conflicting results, with some showing pigs tolerated CO₂ stunning and others showing they did not. However, the current scientific consensus is that the "inhalation of high concentration of carbon dioxide is aversive and can be distressing to animals." Nitrogen has been used to induce unconsciousness, often in conjunction with CO₂. Domestic turkeys are averse to high concentrations of CO₂ but not low concentrations.
;Mechanical : This method can be used for sheep, swine, goats, calves, cattle, horses, mules, and other equines. A captive bolt pistol is applied to the head of the animal to quickly render them unconscious before being killed. There are three types of captive bolt pistols: penetrating, non-penetrating and free bolt. The use of penetrating captive bolts has largely been discontinued in commercial situations to minimize the risk of transmission of disease when parts of the brain enter the bloodstream.
;Firearm : This method can be used for cattle, calves, sheep, swine, goats, horses, mules, and other equines. It is also the standard method for taking down wild game animals such as deer with the intention of consuming their meat. A conventional firearm is used to fire a bullet into the brain or through the heart of the animal to render the animal quickly unconscious.

Killing

;Exsanguination: The animal either has its throat cut or has a chest stick inserted cutting close to the heart. In both these methods, main veins and/or arteries are cut and allowed to bleed.
;Manual: Used on poultry and other animals; different methods are practiced, here are some examples: a) grabbing the bird by the head then snapping its neck using quick and fast movements b) the bird is put upside down inside a metal funnel, then the head is either quickly cut or hit using the back end of a machete or knife. c) cattle, sheep and goats are tied then struck multiple times in the head with a sledgehammer until the animal dies or loses consciousness.
;Drug administration:Drug administration is used to ensure the animal is dead. However, being that this method is expensive, time-consuming, and renders the animals' bodies toxic and inedible, it is mainly used for animal euthanasia, not as a commercialized slaughter method.

Preslaughter handling

Whether animals are stunned before slaughter or not, they suffer stress while waiting to be killed. A 1996 veterinary review found that there are many ways in which animals suffer and die during the preslaughter period. They include:

Dehydration: Animals may not be provided with water at market or during their journey to the slaughterhouse and may arrive dehydrated. The effects of severe dehydration include severe thirst, nausea, a hot-dry body, dry tongue, loss of co-ordination and concentrated urine of a small volume.
Emotional stress during transport: The unfamiliarity of being on board a transport truck causes fear in animals, and if they are cooped up with others who they do not know, they may start fighting. The noise and jolting of the truck also causes stress and cows, pigs, horses and birds are at particular risk of suffering from motion sickness.
Temperature stress during transport: Some animals die because of the heat that develops in the closely confined conditions on board the transport truck. During transport, animals are not able to express all the behaviors which normally allow them to keep cool like seeking shade, wallowing, licking their fur or stretching their wings and legs. During transport the only useful way they can dissipate heat is by panting. In colder climates, the animals can be exposed to extreme low temperatures, resulting in hypothermia.
Torn skin, bruising and injury: Caused by rough handling of animals, such as beating the animals with sticks when they refuse to move forward or dragging them along the ground when they fall down. The insults which lead to bruising may be painful, and the swelling and inflammation associated with a bruise lead to a longer-lasting pain.
Sickness and disease: Farmers vary between countries in their attitude as to which sick and diseased animals can be sent for slaughter. Some take the view that the slaughterhouses are expert at salvaging what they can from carcasses and so most diseased animals are sent in, whereas in other countries farmers appreciate that diseased stock are low grade and their likely low return does not justify sending them in. Sickness and disease are two of the most serious forms of animal suffering and transporting seriously ill animals imposes an additional stress.
Fecal soiling: In some countries, especially where animals come off lush pasture, transport is the main period when they pick up body surface fecal contamination. The emotional stress associated with transport induces defecation and this compounds the problem.
National laws

Europe

The measures for sanitary checks, animal welfare protection and slaughtering procedures are harmonised throughout the European Union, and detailed by the European Commissions' regulations CE 853/2004, 854/2004 and 1099/2009.

Canada

In Canada, the handling and slaughter of food animals is a shared responsibility of the Canadian Food Inspection Agency, industry, stakeholders, transporters, operators and every person who handles live animals.
Canadian law requires that all federally registered slaughter establishments ensure that all species of food animals are handled and slaughtered humanely. The CFIA verifies that federal slaughter establishments are compliant with the Meat Inspection Regulations.
The CFIA's humane slaughter requirements take effect when the animals arrive at the federally registered slaughter establishment. Industry is required to comply with the Meat Inspection Regulations for all animals under their care.
The Meat Inspection Regulations define the conditions for the humane slaughter of all species of food animals in federally registered establishments. Some of the provisions contained in the regulations include:

guidelines and procedures for the proper unloading, holding and movement of animals in slaughter facilities
requirements for the segregation and handling of sick or injured animals
requirements for the humane slaughter of food animals