Intensive pig farming, also known as pig factory farming, is a system of pig production in which pigs are raised indoors at high density under controlled environmental conditions. It has become the dominant method of commercial pork production in most industrialized countries, though traditional systems remain significant in many parts of the world. Typical facilities, sometimes called piggeries, house pigs raised for slaughter in group pens on slatted floors made of concrete, with a manure pit beneath the floor. Breeding sows are kept in gestation crates or in group housing during pregnancy, and moved to farrowing crates to give birth and nurse piglets. The waste falling through the slats is sometimes transferred to manure lagoons.
The system developed over the second half of the 20th century. Features include purpose-built indoor facilities with mechanical ventilation and climate control; specialized genetic lines selected for fast growth, large litter sizes, and feed efficiency; the use of formulated diets heavier in grain than previous practice and with nutrients tailored for each life stage; and routine use of vaccines and antibiotics to manage disease. The new system replaced the mixed outdoor and barnyard operations that had previously dominated. These changes produced substantial gains in feed conversion ratio and growth rate, while requiring fewer human staff per pig. These gains have supported a large expansion in global pork production. Production also became more concentrated, with smallholder farms declining and a growing share of output coming from a smaller number of large operations.
Piglets are usually separated from their mother around 3 weeks old, an earlier weaning than in traditional agriculture, and their diet switched from the sow's milk to solid feed. Other standard practices include tail docking, teeth clipping or grinding, and the surgical castration of male piglets, often performed without anesthesia. Producers cite injury prevention, disease control, and labor efficiency as rationales. These practices, along with close confinement of sows, have drawn sustained criticism from animal welfare researchers and advocacy groups. The European Union restricts the use of gestation crates to the first four weeks of pregnancy, and several U.S. states, including California and Massachusetts, have passed laws limiting confinement of breeding sows. Most other states of the United States permit broader use of crates, as do other major producers including China, Brazil, and Mexico.
Because intensive operations concentrate large numbers of animals and their manure in small areas, they are associated with more acute environmental impacts from pig farming than traditional pig farming, including water pollution from nutrient runoff and air pollution from ammonia released by manure storage. The routine use of antibiotics in intensive systems has also been linked to the spread of antibiotic-resistant bacteria that can infect humans. The high density of genetically similar animals raises concerns about the potential amplification of zoonotic diseases such as swine influenza ("swine flu").
Description
Intensive piggeries are generally large warehouse-like buildings or barns with little exposure to sunlight or the outdoors. Most pigs are officially entitled to less than one square meter of space each. Indoor pig systems allow many more pigs to be monitored than historical methods, ensuring lowered cost, and increased productivity. Buildings are ventilated and their temperature regulated.
Most domestic pig varieties are susceptible to sunburn and heat stress, and all pigs lack sweat glands and cannot cool themselves. Pigs have a limited tolerance to high temperatures and heat stress can lead to death. Maintaining a more specific temperature within the pig-tolerance range also maximizes growth and growth-to-feed ratio. Indoor piggeries have allowed pig farming to be undertaken in countries or areas with unsuitable climate or soil for outdoor pig raising. In an intensive operation, pigs no longer need access to a wallow (mud), which is their natural cooling mechanism. Intensive piggeries control temperature through ventilation or drip water systems.
The way animals are housed in intensive systems varies, and depending on economic viability, dry or open time for sows can sometimes be spent in indoor pens or outdoor pens or pastures.
The pigs begin life in a farrowing or gestation crate, a small pen with a central cage, designed to allow the piglets to feed from their mother, the sow, while preventing her from moving around, crushing her children, and reducing aggression. The crates are so small that the pigs cannot turn around.
The Vegetarian Society has stated that artificial insemination is much more common than natural mating, as it allows up to 30–40 female pigs to be impregnated from a single boar. Workers collect the semen by masturbating the boars, then insert it into the sows via a raised catheter known as a pork stork. Boars are still physically used to excite the females prior to insemination, but are prevented from actually mating.
When confirmed pregnant, sows are moved to farrowing crates, with litter, and will spend their time in gestation crates from before farrowing until weaning. Injections with a high availability iron solution often are given, as sow's milk is low in iron. Vitamin D supplements are also given to compensate for the lack of sunlight. As the sows' bodies become less capable of handling the large litter sizes encouraged by the industry, the frequency of stillborn piglets generally increases with each litter. These high litter sizes have doubled the death rates of sows, and as many as 25%–50% of sow deaths have been caused by prolapse, the collapse of the sow's rectum, vagina, or uterus, which can lead to other health problems, including a miscarriage. Pig breeders repeat the cycle of impregnation and confinement for about 3 to 5 years or until the sow succumbs to her injuries, at which point she is then slaughtered for low-grade meat such as pies, pasties and sausage meat.
Of the piglets born alive, 10% to 18% will not make it to weaning age, succumbing to disease, starvation, dehydration, or being accidentally crushed by their trapped mothers. This death toll includes the runts, unusually small piglets who are considered economically unviable and killed by staff, typically by thumping meaning blunt trauma to the head.
Piglets often have the following performed: castration, earmarking, tattooing for litter identification, tail docking, teeth clipping to prevent cannibalism, instability, aggression, and tail biting that is induced by the cramped environment. Because anesthetic is not legally mandated and often economically unviable, these invasive procedures are usually done without any pain killers. While wild piglets remain with their mothers for around 12 to 14 weeks, farmed piglets are weaned and removed from their mothers at between two and five weeks old. They are then placed in sheds, nursery barns or directly to growout barns. While capable of living 10–12 years, most pigs are slaughtered when they are 5–6 months old.
Indoor systems allow for the easy collection of waste. In an indoor intensive pig farm, manure can be managed through a lagoon system or other waste-management system. However, waste smell remains a problem which is difficult to manage. Pigs in the wild or on open farmland are naturally clean animals.
Statistics
In the UK there are around 11,000 pig farms. Approximately 1,400 of these units house more than 1,000 pigs and contain about 85% of the total UK pig population. Because of this, it was reported in 2016 that the vast majority of the pork products sold in the UK come from intensive farms.
In Australia, there were around 50,000 pig farms in Australia in the 1960s. Today, there are fewer than 1,400, and yet the total number of pigs bred and slaughtered for food has increased. As of 2015, 49 farms housed 60% of the country's total pig population.
In the United States, three-quarters of pork comes from large operations with 5,000 or more pigs. The animals are most often kept in crowded confinement buildings without fresh air or sunshine.
Environmental impacts
Intensive pig farming adversely affects the surrounding environment, mainly driven by the spread of feces and waste to surrounding neighborhoods, polluting air and water with toxic waste particles.
Regulation Many countries have introduced laws to regulate treatment of intensively farmed pigs. However, there is no legal definition for free-range pigs, so retailers can label pork products as free-range without having to adhere to any standards or guidelines. Only 3% of UK pigs spend their entire lives outdoors.
European Union As of 2016, The European Union legislation has required that pigs be given environmental enrichment, specifically they must have permanent access to a sufficient quantity of material to enable proper investigation and manipulation activities.
Under the legislation tail docking may only be used as a last resort. The law provides that farmers must first take measures to improve the pigs' conditions and, only where these have failed to prevent tail biting, may they tail dock.
United States As of 2023, ten states have banned the use of gestation crates: Arizona, California, Colorado, Florida, Maine, Massachusetts, Michigan, Ohio, Oregon, and Rhode Island. Proposition 12, a California ballot measure passed in 2018, also bans the sale of whole, uncooked pork cuts throughout the state if the producers are noncompliant with the ban, affecting both in-state and out-of-state pig farmers.
Discharge from concentrated animal feeding operations (CAFOs) is regulated by the federal Environmental Protection Agency (EPA). In 2003, EPA revised the Clean Water Act to include permitting requirements and discharge limitations for CAFOs. , EPA revised the National Pollutant Discharge Elimination System (NPDES) by requiring CAFOs to apply for permits before they can discharge manure.
The federal Humane Slaughter Act requires pigs to be stunned before slaughter, although compliance and enforcement is questioned. There is concern from animal liberation and welfare groups that the laws have not resulted in a prevention of animal suffering and that there are "repeated violations of the Humane Slaughter Act at dozens of slaughterhouses".
Criticism
Dispute regarding farming methods Intensive piggeries have been negatively contrasted with free range systems. Such systems usually refer not to a group-pen or shedding system, but to outdoor farming systems. Those that support outdoor systems usually do so on the grounds that they are more animal friendly and allow pigs to experience natural activities (e.g., wallowing in mud, relating to young, rooting soil). Outdoor systems are usually less economically productive due to increased space requirements and higher morbidity, (though, when dealing with the killing of piglets and other groups of swine, the methods are the same.) They also have a range of environmental impacts, such as denitrification of soil and erosion. Outdoor pig farming may also have welfare implications, for example, pigs kept outside may get sunburnt and are more susceptible to heat stress than in indoor systems, where air conditioning or similar can be used. Outdoor pig farming may also increase the incidence of worms and parasites in pigs. Management of these problems depends on local conditions, such as geography, climate, and the availability of skilled staff.