Pigs — cognition and industry

A pig is not a simplified version of a larger animal. Sows raise their young in elaborate nest structures when given the space. Piglets learn from watching other piglets. Adult pigs remember the locations of food for weeks, track which conspecifics have seen what, and respond to their own names. The scientific picture of who they are has sharpened considerably over the last two decades, even as the industrial systems that raise roughly 1.4 billion of them each year have largely hardened in place (FAOSTAT).

This article pulls the two halves together: what is known about pig minds, and what is done to pig bodies.

What modern science says about pig cognition

The most comprehensive review is Marino and Colvin’s “Thinking pigs” (Marino and Colvin, 2015), published in the International Journal of Comparative Psychology. Drawing on decades of experimental and ethological work, the paper documents long-term memory, discrimination learning, use of simple symbolic cues, spatial and temporal reasoning, responsiveness to joysticks and computer-based tasks, behavioral signatures of emotion, distinctive individual personalities, and complex social lives. Pigs, the authors conclude, “share a number of cognitive capacities with other highly intelligent species.”

Mendl, Held, and Byrne (2010), in a Philosophical Transactions of the Royal Society B synthesis on pig cognition, emphasize the social cognitive side — how pigs form relationships, track dominance, and coordinate with or exploit one another. Their earlier empirical work showed that subordinate pigs, when following a dominant to hidden food, adjust their behavior to avoid being followed and displaced in turn (Held et al., 2002). The setup is a form of tactical social cognition: pigs change what they do based on what another pig knows.

Related work on negative welfare states has found that tail biting — one of the chronic behavioral pathologies of intensive systems — is linked to individual fearfulness and serotonergic profiles (Ursinus et al., 2014), suggesting that the “vice” is a signal of psychological state rather than mere mechanical irritation.

The upshot, repeated across the literature: pigs are cognitively substantial animals with emotional lives that respond, measurably, to the environments we put them in.

The environments we put them in

Industrial pig production takes an animal evolved for rooting, wallowing, nest-building, and long-distance foraging, and compresses it into a life of concrete, metal, and slatted floors. The European Food Safety Authority’s 2007 Scientific Opinion on fattening pigs (EFSA, 2007) and its updated 2022 opinion on the welfare of pigs on farm (EFSA, 2022) document the practices in detail. Several recurring features define the system.

Gestation crates (sow stalls). Breeding sows are confined in metal-barred stalls roughly the size of their bodies for most or all of their pregnancy — unable to turn around, take more than a step, or build a nest. EFSA (2022) concludes that individual stalls cause serious welfare problems and recommends group housing with loose farrowing systems.

Farrowing crates. Around birth and during lactation, sows are moved to a second type of crate designed to reduce piglet crushing. The sow lies on her side; piglets nurse through bars. The confinement suppresses nest-building — a motivationally powerful behavior in sows — and EFSA (2022) again calls for transition to free-farrowing and pen systems.

Tail docking. Piglets’ tails are routinely cut off, usually without anaesthesia, to reduce tail biting in crowded pens. EFSA (2007, 2022) is explicit that tail docking should not be performed routinely and that the underlying cause is barren, overstocked housing. In the EU, routine docking has been formally prohibited since Council Directive 2008/120/EC, yet the practice persists on the great majority of commercial farms across member states.

Castration. Male piglets are commonly castrated — traditionally without anaesthesia — to prevent “boar taint” in meat. Alternatives (immunocastration, raising entire males, surgical castration with pain relief) exist and are used in some markets but not universally.

Slaughter. At the end of the line, pigs in large plants are typically stunned with carbon dioxide or electrical current before exsanguination. High-concentration CO2 stunning is aversive — pigs show strong avoidance, gasping, and escape attempts during induction — and EFSA has repeatedly flagged it as a welfare concern while noting the absence of scaled alternatives.

Layered onto these specific practices are the baseline conditions of intensive systems: barren pens, slatted floors, weaning at two to four weeks (versus a natural weaning age of several months), genetic lines selected for rapid growth and large litters, and lifespans truncated to roughly six months for a species that can live well over a decade.

Scale

FAOSTAT records approximately 1.4 billion pigs slaughtered each year globally, with China, the European Union, the United States, Brazil, and Vietnam as the largest producers. The great majority are raised in intensive, indoor, confinement-based systems. Outdoor, pasture-raised, and small-scale husbandry together account for a small fraction of global production.

Pig production is also concentrated by firm. In the United States, a handful of integrators contract with thousands of grower farms; in the EU and China, similar consolidation has unfolded over the last two decades. The system that EFSA describes is not a collection of local practices — it is a single global industrial pattern with regional variants.

EU bans versus US status

The regulatory picture diverges sharply between jurisdictions.

In the European Union, Council Directive 2008/120/EC prohibits the use of individual gestation stalls after the first four weeks of pregnancy and forbids routine tail docking and teeth clipping. Enforcement is uneven, and the European Commission’s own audits have repeatedly found widespread non-compliance on docking in particular. The EFSA 2022 opinion explicitly calls for further reforms: loose farrowing, group housing for the whole gestation period, more space, and enrichment sufficient to satisfy rooting and exploration.

In the United States, there is no federal law governing the on-farm welfare of pigs. The Humane Methods of Slaughter Act applies at the slaughterhouse door but excludes poultry and does not regulate raising conditions. Gestation crates remain standard in most of the country.

State-level reform has been the main lever. California’s Proposition 12 (2018) prohibits the sale in California of pork produced using gestation crates, regardless of where the pigs were raised. The pork industry challenged the law under the dormant Commerce Clause, arguing that a large-market state could not impose production standards on out-of-state producers. In National Pork Producers Council v. Ross, 598 U.S. 356 (2023), the Supreme Court upheld Proposition 12. The decision is the most consequential U.S. farm-animal welfare ruling of the last generation: it confirms that states may condition market access on humane production standards, opening the door to broader reform.

Massachusetts’s Question 3 (2016, updated 2021), several retailer pledges, and the accelerating McDonald’s, Smithfield, and Tyson commitments to phase out gestation crates are part of the same wave — partial, slow, and heavily contested, but moving.

What the reform picture leaves unfinished

Even a fully Prop-12-compliant, EU-directive-compliant pig farm still confines highly cognitive animals for roughly six months of their lives, in spaces orders of magnitude smaller than their natural range, with tail docking continuing in practice, routine early weaning, CO2 stunning at slaughter, and genetics selected for production rather than welfare. The welfare reforms of the last twenty years are meaningful for individual animals and still leave the central fact intact: an animal whose cognitive and emotional life the scientific literature (Marino and Colvin, 2015; Mendl, Held, and Byrne, 2010) treats as substantial is produced, at industrial scale, for a single terminal use.

That gap — between what the science says pigs are, and what the system does to them — is the specific weight that the animals pillar, and factory farming as a concept, are meant to carry.