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This article provides summarized information about farmed pigs in the context of animal rights, including injustices and suffering, humane labels and certifications, pig sentience and cognition, the environmental consequences of farming pigs, the health risks of pig meat, and impacts to communities and workers.

General Information


Pigs were domesticated approximately 9000 years ago from various subspecies of the Eurasian wild boar.[1] Domestication occurred separately in Europe and Asia, though there is evidence that interbreeding later took place.[2] Pigs were brought to North America by Spanish explorers in the 16th century.[3]


Worldwide, over two billion pigs are slaughtered for meat each year. In the United States alone, over 121 million are killed annually.

Using data from the USDA Census of Agriculture and the EPA's definitions of Concentrated Animal Feeding Operations, the Sentience Institute estimates that 98.3 percent of pigs in the USA are factory-farmed.[4] The figures for other industrialized nations are likely to be similar.

Injustices and Suffering

The injustices inherent in exploiting pigs and other non-human animals stem from seeing them as commodities having only instrumental value, lacking any inherent worth apart from their usefulness to humans.

As Tom Regan put it, the animals we use "have a life of their own that is of importance to them, apart from their utility to us. They are not only in the world, they are aware of it and also of what happens to them. And what happens to them matters to them. Each has a life that fares experientially better or worse for the one whose life it is."

As shown in the section on sentience and cognition, pigs not only have a will to live and value their lives, just as humans do, but also have desires, preferences, emotions, families, social communities, natural behaviors, a sense of themselves, and a sense of the future.

The injustices discussed below—all arising from a failure to recognize the inherent worth of other sentient beings—are either standard practice or not unusual. And, as shown in the section below on humane labels and certifications, this is true even for products with a humane label or certification. To omit a significant number of these injustices would likely render the cost of such products unaffordable by all but the most affluent, and we would still have to slaughter them.

Loss of Life

We have no nutritional need for pork, so denying pigs their lives is unnecessary, as are the other forms of suffering enumerated here. Not only are we taking their lives—we are doing so after allowing them to live only about three percent of their natural life spans. Pigs are slaughtered after living only 5 to 6 weeks of a 10 to 12-year natural lifespan.

To take the life of any sentient being is to harm that being by depriving them of opportunities for fulfillment, even if it is done suddenly and painlessly (which it is not, as explained below).


Boiling Alive

Many slaughterhouses kill 1000 pigs or more per hour, and the USDA is attempting to remove limits on slaughter line speeds.[5] Legally, pigs are required to be rendered unconscious by stunning before slaughter. However, lines run so quickly that mistakes are inevitable. Many pigs are not properly stunned, and investigations show that as a consequence they are still conscious when they reach the scalding tanks which remove their hair.[6] This means they are effectively boiled alive.

Gas Chambers

Increasingly, pigs are slaughtered in carbon dioxide gas chambers rather than conventional slaughterhouses.[7] This is considered the most humane method of slaughter, but undercover footage shows pigs panicking, gasping for air, and trying to escape.[8] Studies show that this form of slaughter causes both anxiety and pain in pigs.[9]


Teeth Clipping

Piglets may also have their sharp “needle teeth” clipped to prevent them from injuring each other when fighting over teats, inducing severe pain in pigs as it would in humans.[10] Teeth clipping can also result in lasting damage. According to the American Veterinary Medical Association, "clipping has been shown to increase longer-term behaviors suggestive of discomfort such as chomping. Piglets whose teeth have been clipped may experience more gum and tongue injuries, and potentially painful inflammation or abscesses of the teeth."[11]


Male piglets are castrated, primarily because their flesh can otherwise develop an unpleasant taste and smell. This is generally done by making an incision in the scrotum and pulling out the testes, before cutting the spermatic cord. In most countries, it is legal to carry out this procedure without anesthetic in the piglet's first week of life, despite the fact that this is known to be painful. Carrying out castration at this age is also risky as the testes are very small, which can lead to incomplete castration and increase the risk of prolapse of the intestine.[12]

Tail Docking

Pigs sometimes bite each other's tails when stressed, so some farmers cut off pigs' tails to prevent this. However, studies suggest that this can cause acute and possibly chronic pain.[13] Though tail docking is thought to reduce the incidence of serious injuries, it does not eliminate them. In Ireland, where 99 percent of pigs have docked tails, 72.5 percent were still found to have tail lesions at slaughter.[14]

Ear Notching and Tattooing

Most piglets undergo painful routine procedures when they are less than a week old so they can be identified.

Ear notching is painful.[15] Tattooing involves some degree of pain, but perhaps, more importantly, it is stressful.[16] Unlike humans, when pigs are tattooed they are not consenting and don't understand what's happening to them.

Living Conditions

Gestation Crates

Pregnant sows are often kept in metal stalls called gestation crates. The crates typically measure just 6.5 ft x 2.0 ft, meaning sows are not able to turn around.[17] Some larger sows are not even able to lie on their sides (the way pigs normally sleep) in the crates. The stalls typically do not contain bedding material, instead having metal, plastic, or concrete floors. Sows often chew on the bars, a sign of boredom and frustration.[18] Pigs prefer to relieve themselves a long way from where they eat and sleep, which is impossible when they are confined to crates.[19]

Farrowing Crates

A few days before they are due to give birth, sows are moved to farrowing crates. These are slightly larger to allow the sow to lie on her side and nurse her piglets. They also have an additional enclosure attached to prevent piglets from being accidentally crushed by the sow. The crates are said to reduce piglet mortality compared to keeping sows loose, but there is no convincing evidence that this is the case.[20] Sows remain in farrowing crates for about a month, before being impregnated again and returned to the gestation crates. Gestation crates have been banned in nine US states, but farrowing crates remain legal across the country. Use of the crates has also been banned or restricted in many other regions, such as the EU and Canada.[21]

Crowded Pens

After being removed from their mothers, piglets are crowded into pens where they barely have room to move until they reach slaughter weight. Pigs may also develop arthritis from lack of exercise and be injured when their feet are caught in the floor slats. The stress of confinement can lead pigs to exhibit unnatural cannibalistic behavior.[22]

Disease and High Mortality

African Swine Fever

African swine fever is one example of pigs' susceptibility to disease because of crowded filthy conditions. It has an extremely high mortality rate of 95-100 percent in pigs. There is no known treatment for the disease.[23] An outbreak in China in mid-2019 resulted in the deaths of millions of pigs.[24]

Pneumonia and Mange

Pneumonia and mange are other examples.[25] Mortality rates are high, and investigations have found that their bodies are sometimes left in the pens for extended periods.[26]

Reproduction and Selective Breeding

Large Litters

Modern sows have been bred to produce significantly larger litters than their wild counterparts. A study done on wild boars in Portugal found that litter sizes ranged from 2 to 8 piglets.[27] Farmed sows produce far larger litters. Between 1986 and 2006, the average number of live piglets per litter increased from 10.5 to 12.7. The time between litters also decreased from 155.8 days to 148.7 days. Suckling so many piglets can put immense strain on the sow and cause her to lose body weight.[28]

Weight Gain

Like factory-farmed chickens, pigs have been bred to gain weight so rapidly that they sometimes struggle to support their own body weight. On average, pigs who are being fattened now gain 770g a day, compared to 670g two decades ago. This rapid weight gain can lead to joint and leg problems.[28] In 1997, a study showed that pigs more closely related to wild boar gained 47g less per day.[29]

Pigs' increased muscle mass means their hearts and lungs are proportionally smaller than those of their ancestors, which can cause strain. As a result, even young pigs sometimes die from heart attacks.[30] Selective breeding for lean muscle has led to the prevalence of a gene which makes pigs very sensitive to stress.[28]

Artificial Insemination

The use of artificial insemination rather than natural breeding is common,[31] as it gives farmers more control over the characteristics of the piglets. Artificial insemination is a stressful procedure[32] that sows cannot consent to, making it a violation of their rights.

Cruel Handling

Prior to slaughter, many pigs become nonambulatory. This is thought to be due to the stress of transport and handling combined with the change of environment.[33] Pigs who are unable to move may be beaten, dragged, or shocked with electric prods to move them through the killing line.[6]

It's not just in the slaughterhouse that such abuses occur. Undercover investigations have shown that pigs on factory farms endure cruel, rough handling. Multiple investigations conducted by Mercy for Animals and others have recorded pigs being:[34]

  • punched
  • kicked
  • beaten
  • shouted at
  • having their hair pulled out
  • violently shaken
  • poked in the eyes
  • hit with wooden boards.

Sick piglets were denied veterinary care and thrown into piles and left to die slowly.[34]


Pigs are often transported hundreds of miles in extreme temperatures to be slaughtered. This can lead to deaths due to frostbite or heat stress.[35] Legally, pigs can be transported for up to 28 hours at a time with no rest, food, or water. This has been shown to be very stressful.[36]

Being transported is also stressful for pigs. In particular, they find vibration very uncomfortable and often suffer from travel sickness.[37]

Pigs Left to Die after Natural Disasters

In the USA, factory-farmed pigs have been left to die in the floods following major hurricanes. For example, an estimated 5500 pigs drowned following Hurricane Florence,[38] and thousands more were killed by Hurricane Floyd.[39]

Humane Labels and Certifications

Investigations by Consumer Reports and the Open Philanthropy Project (and others) reveal that humane-sounding labels and certifications are largely meaningless, as shown below. In general, these investigations reveal that the standards are weak and unenforced, audits and inspections are rarely done, and if they are done and violations are found, which is infrequent, no one gets fined.[40][41]

North American Meat Guidelines

Some certifications rely on the North American Meat Institute slaughter guidelines for standards relating to slaughter. These allow pigs to be slaughtered in carbon dioxide gas chambers or conventional slaughterhouses. When gas chambers are used, it is considered acceptable for pigs to gasp for breath or exhibit “strange vocalization and sudden, involuntary reflexes including muscle jerks or twitches.”[44] Evidence shows that in conventional slaughterhouses, pigs are often improperly stunned.[45]

Global Animal Partnership 5-Step Certification

The Open Philanthropy Project criticized Whole Foods' Global Animal Partnership (GAP) for having weak enforcement and for providing only slight improvements over standard factory farming conditions.[46]

Certified Humane Raised and Handled

Consumer Reports says that "we do not rate Certified Humane as a highly meaningful label for animal welfare, because the standards do not have certain requirements that a majority of consumers expect from a 'humanely raised' label, such as access to the outdoors."[47]

Animal Welfare Approved Standard

On their Greener Choices website, Animal Welfare Approved is the only certification that Consumer Reports says has strong standards, yet the standards still allow for mutilations[48] and other injustices.

Also, products with this label are challenging to find. A search using their own product finder reveals that it's unlikely you will find any products with this label at a grocery store near you.[49]

American Humane Certified

According to Consumer Reports, "the requirements fall short in meeting consumer expectations for a 'humane' label in many ways."[50]

Sentience and Cognition

While we are not suggesting that the degree of moral consideration given to an animal be based on their cognitive capacity, it seems that most people are not fully aware of the rich cognitive, emotional, and psychological lives that pigs experience.

Object Recognition and Long-Term Memory

Studies have shown that pigs can distinguish between objects and remember objects for at least five days. This shows that they have long-term memory. They are also able to think abstractly, learning the meaning of symbols representing actions and objects. In one experiment, pigs were able to understand and respond to combinations of symbols that represented phrases such as “fetch the ball.”[51] They have also been recorded using tools.[52]

Anticipation of the Future

Few studies have been done on time perception in pigs, but there is evidence that they can anticipate the future. For example, one study found that pigs reacted negatively with high-pitched vocalizations when they knew a negative event was coming.[51]

Cognitive Complexity

Dr. Donald Broom of the University of Cambridge has been quoted as saying that pigs are cognitively capable of being more sophisticated than three-year-olds.[53]

Pigs also engage in play, considered to be an indication of cognitive complexity. When raised without enough stimulation, they can develop behavioral abnormalities. They have been shown to make more positive decisions when given more stimulation, which is evidence that environmental enrichment can make them more optimistic.[51] They are also skilled at using spatial information — navigating mazes, for example.[51]

Awareness of Self and Others

Studies show that pigs can discriminate between individuals, whether human or other pigs. Pigs in some studies have been able to find food that was only visible in a mirror. They have also been taught to play video games, controlling the joysticks with their mouths or snouts. This provides some evidence of self-awareness, as the pigs understood that their actions were causing the cursor to move. Many animals, such as dogs, do not show these capabilities.[51]

Emotional Lives and Personality Traits

In one study, some pigs were trained to anticipate negative events when a certain piece of music was played. Others were not trained but exhibited similar stress responses to the nearby trained pigs when the music was played. This provides evidence that pigs can recognize and pick up on each other's emotions, which may mean they experience empathy. It also shows that they have a sense of the future. Additionally, pigs show a range of personality traits such as sociability, exploration, and aggression.[51]

Environmental Consequences

The breeding, confinement, and slaughter of pigs have a profoundly negative impact on the environment.


Factory farms raise thousands of pigs at a time, and each one produces 2-4 times as much waste as a human. The production of such huge quantities of waste in a relatively small area makes it difficult to manage effectively. Usually, waste from industrial pig farms is dumped untreated into vast lagoons that may leak or overflow.[54]

Untreated pig waste is often spread over nearby fields in an attempt to dispose of it. These excessive amounts of manure can pollute the soil. When the soil becomes saturated, manure may run off the fields and into waterways. This, along with overflow from lagoons, can contaminate water and kill fish. Pollutants from pig slaughterhouses may also be released into waterways.[54]

Waste lagoons and the spraying of manure pollute the air with toxins and greenhouse gases such as hydrogen sulfide, methane, and ammonia.[54] Nitrogen in the waste may also contribute to acid rain.[55]


After flowing into rivers, nitrogen from manure can reach lakes and oceans, where it causes algae to bloom and use up much of the oxygen in the water. This process is known as eutrophication, and it makes it difficult or impossible for other aquatic species to survive.[54]

Feed Production

Factory-farmed pigs are fed largely on grains, which also causes environmental problems. Huge areas of land are needed to grow this grain, leading to deforestation and habitat destruction. According to the FAO, 47 percent of emissions from pig-rearing are caused by feed production. Another 13 percent is related to land-use change due to the growing of crops.[56] Large quantities of water, fertilizers, and fossil fuels are also used in this process.[57] Farmed pigs are also sometimes fed on fishmeal,[58] contributing to overfishing.

Human Health and Nutrition

Food Safety

Though USDA inspectors must legally be present at slaughterhouses, some inspectors complain that the design of plants makes it impossible for them to see the slaughter area. Because of the speed of the lines, it is also very difficult for inspectors to spot abnormalities or diseases in the carcasses.[59]


Cardiovascular Disease

Pig meat contains saturated fat, cholesterol, and heme iron, which contribute to an increased risk of heart disease.[60][61][62][63] In 2012, a meta-analysis concluded that both red and processed meat are linked to an increased risk of stroke.[64] A Finnish study carried out between 1972 and 1992 found that heart disease rates in the country dropped dramatically when the intake of saturated fat and cholesterol decreased.[65]


In 2015, the World Health Organization (WHO) evaluated 800 studies and concluded that processed meat (such as sausages, bacon, and ham) is a Group 1 carcinogen, meaning it definitely causes cancer. The processing and cooking of meat was found to form various carcinogenic chemicals.[66] Other Group 1 carcinogens include tobacco and asbestos.[67]

The report also concluded that unprocessed red meat (including pig meat) is Group 2A carcinogen, meaning it is a probable cause of cancer. It has been linked to colorectal, prostate, and pancreatic cancer.[66]

Type 2 Diabetes

Red meat is associated with an increased risk of Type 2 diabetes, especially if it is processed. This is thought to be because it contains high levels of fat, heme iron, nitrites, and other harmful substances.[68]

Animal Protein Risks

All animal protein, pig meat or otherwise, carries risks that are not associated with plant protein. A review by Dr. Sofia Ochoa cites 42 studies showing that animal protein:[69]

  • elevates hormone-insulin-like growth factor-1 (IGF-1), which stimulates cell division and growth in both healthy and cancer cells and "has been consistently associated with increased cancer risk, proliferation, and malignancy"
  • "results in us having higher circulating levels of trimethylamine N-oxide (TMAO)," which "injures the lining of our vessels, creates inflammation, and facilitates the formation of cholesterol plaques in our blood vessels"
  • causes the overproduction of the hormone fibroblast growth factor 23 (FGF23), which damages our blood vessels, can "lead to enlargement of the cardiac ventricle, and is associated with heart attacks, sudden death, and heart failure"
  • can result in the overabsorption of heme iron, causing the conversion of other oxidants into highly reactive free radicals that "can damage different cell structures like proteins, membranes, and DNA" (heme iron "has also been associated with many kinds of gastrointestinal cancers")
  • can result in a higher incidence of bone fractures because of animal protein's high concentrations of sulfur
  • contributes to atherosclerosis—plaques of cholesterol that accumulate in the lining of our vessels; this condition is far less common on a vegan diet because absorbable cholesterol is not found in plants

Social Consequences of Pig Production

The vast majority of pigs in industrialized nations are raised on factory farms. This has profound consequences for those who live nearby. The farms are disproportionately located in low-income communities inhabited largely by ethnic minorities.[70][71]

Foul Odors

One of the most studied cases is in North Carolina, the second-largest hog-producing state. Those who live near factory farms complain of foul odors that invade their homes and force them to cover their mouths and noses when they step outside. Some even spend nights in motels to escape it if they can afford to do so. The smell can permeate clothes and upholstery, making it difficult to remove.[72]

Land and Water Contamination

Contamination from airborne manure: Excess manure from factory farms is spread over nearby fields. In some areas, manure is spread so close to communities that a mist of it covers houses, cars, and laundry left out to dry.[72]

Contimination of water supply: Other waste is stored in lagoons, which can leak or overflow and contaminate the local water supply.[54]

Health problems from manure: Factory-farmed pig manure often contains pathogens, antibiotic-resistant bacteria, toxic chemicals, and heavy metals, which can cause illness if inhaled or ingested.[54][71] Studies show that these substances can contribute to decreased quality of life, higher blood pressure,[73] respiratory problems, and mental stress. The odors can also lead to headaches, nausea, and vomiting, among other symptoms.[74] Factory farm workers may also have an increased risk of health problems, such as asthma.[75]

Exploitation of Slaughterhouse Workers

Slaughterhouse workers have some of the highest injury rates of any industry, as lines move at unsafe speeds and workers handle very sharp knives. Several workers have even been killed in US slaughterhouses. Workers are also prone to repetitive strain injuries from repeating the same movements for hours on end. They are often dismissed when they become injured, leading many to hide their injuries and continue working.[76]

Those who work in slaughterhouses are often undocumented immigrants who speak little English. They may not be aware of their rights and often fear deportation if they try to improve their conditions. Workers may be forced to work excessively long shifts and threatened with dismissal if they refuse. Some are expected to work as much as twelve hours a day, six days a week. This can lead to fatigue and depression.[76]

Violence in Slaughterhouse Communities

Committing violent acts against animals leads many workers to develop post-traumatic stress disorder (PTSD).[77] It may also lead them to commit violence against humans. Rates of violent crime, including domestic abuse and rape, are higher in communities located near a slaughterhouse.[78]


This article was originally authored by Bethany Chester with contributions by Greg Fuller . The contents may have been edited since that time by others.


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