Pigs do eat each other under certain conditions, though the behavior ranges from chronic low-level biting of tails and ears in farm settings to outright scavenging of dead conspecifics in the wild. True cannibalism, where a pig consumes the flesh of another pig, has been documented in wild boar populations visiting carcasses, and the gnawing and tissue consumption that follows severe tail-biting outbreaks on farms can cross into the same territory. The science behind it involves a tangle of nutritional deficiency, chronic stress, genetics, and environment, and the problem has resisted simple solutions for decades.
Tail Biting as the Entry Point
When people ask whether pigs eat each other, the answer usually starts with tail biting. This is the most common and most studied form of harmful pig-on-pig behavior on farms. It begins with one pig mouthing or chewing another’s tail, and it can escalate into tissue loss, open wounds, and, in severe cases, consumption of the tail itself. In one study of 89 pre-finishing piglets observed closely over a research period, tail-biting events were recorded 420 times. The overwhelming majority of those interactions were gentle enough that the receiving pig did not visibly react, but about 8% provoked a pain response.1Frontiers in Veterinary Science. Individual behavioral correlates of tail biting in pre-finishing piglets What stands out is how widespread the behavior was: roughly 83% of pigs in that study performed tail biting at some point, and about 80% received it. Only 2% of pigs were completely uninvolved.
Tail biting sits on a spectrum. At the mild end, it looks like idle mouthing, barely distinguishable from the exploratory rooting behavior pigs direct at everything around them. At the severe end, it produces deep wounds, partial or total tail loss, and secondary infections that can kill the animal. The transition from mild to severe can be abrupt: a barn that seems stable one week can erupt into an outbreak the next, often triggered by something environmental. The behavior is not neatly divided into aggressors and victims, either. In that same study, 72% of observed pigs were both biters and victims, swapping roles depending on the circumstances.1Frontiers in Veterinary Science. Individual behavioral correlates of tail biting in pre-finishing piglets
Tail biting is not the only target. Pigs also bite ears, flanks, and other body parts. Flank biting produces characteristic skin lesions on the ribs, upper legs, and shoulders of pigs as young as ten to twelve weeks. Ear-tip lesions, sometimes called porcine necrotic ear syndrome, can appear in weaners and persist through the growing period. Histological examination of both flank and ear-tip lesions reveals the same progression of tissue damage, from thickened skin with inflammatory cell infiltration to full ulceration.2PubMed Central. Lesions of so-called flank biting and necrotic ear syndrome in pigs
Nutritional Deficiency and the Attraction to Blood
One of the more unsettling findings in pig behavior research is that dietary inadequacy makes pigs measurably more attracted to blood. In controlled experiments, pigs fed a diet lacking protein supplement for four weeks showed a dramatic increase in attraction to blood-covered surfaces, along with reduced weight gain.3Canadian Journal of Animal Science. Enhanced attraction to blood by pigs with inadequate dietary protein supplementation When synthetic amino acids were added back to the deficient diet, the results were mixed: pigs that regained normal growth rates showed lower blood attraction, while those still growing slowly tended to remain drawn to blood. The researchers proposed that the growth depression itself, not just the missing nutrients, predisposed pigs to seek out blood, possibly as a way of compensating for whatever the body was lacking.
Mineral deficiency tells a similar story with a more specific culprit. Pigs receiving a diet stripped of all mineral supplements showed a pronounced increase in chewing a blood-covered model. When the researchers tested individual minerals, the biggest driver turned out to be salt. Removing only iodized salt from the diet produced nearly the same heightened blood attraction as removing all minerals, while removing everything except salt caused a much smaller and statistically insignificant change.4Canadian Journal of Animal Science. Mineral-deficient diets and the pig’s attraction to blood: implications for tail-biting This makes biological sense: blood is salty, and a pig craving salt would find a wounded tail especially interesting. The implication for farms is clear. Even a temporary lapse in feed quality can set the stage for an outbreak of biting, and once a tail wound opens and bleeds, the salt in the blood can draw more attention from penmates.
Stress, Cortisol, and the Biter’s Brain
Stress is deeply intertwined with biting behavior, though the relationship is not as simple as “stressed pigs bite more.” Research on saliva biomarkers found that pigs who were active tail biters had higher cortisol levels than control pigs, supporting the intuitive link between stress and aggression. Meanwhile, pigs with tail-biting lesions (the victims) showed elevated markers of infection and inflammation, including higher levels of haptoglobin, confirming that tail wounds serve as entry points for bacteria.5PubMed. Novel saliva biomarkers for stress and infection in pigs: Changes in oxytocin and procalcitonin in pigs with tail-biting lesions
An interesting wrinkle comes from work examining how different pig “phenotypes” respond to a standard stress test. Victim pigs, those habitually on the receiving end of biting, showed a blunted cortisol response to a novel-object test compared to biters and neutral pigs.6bioRxiv. A trait or a state – how consistent are tail biting phenotypes in pigs? Biters and neutral pigs both had higher cortisol spikes after the stressor. This suggests that victims are not simply the weakest or most passive animals in a pen; they may differ physiologically in how they process and respond to stress, which could make them less reactive and therefore easier targets.
When the Barn Itself Is the Problem
Pigs are intensely curious animals with a strong drive to root, forage, and explore. In barren housing with concrete floors and nothing to manipulate, that drive has nowhere to go. The prevailing theory is that tail biting represents a redirection of natural rooting behavior toward penmates in the absence of suitable substrates.7PubMed Central. A Review of the Effects of Non-Straw Enrichment on Tail Biting in Pigs This is likely only one of many contributing causes, but it explains why enrichment materials, things pigs can chew, root, and tear apart, consistently reduce biting.
Air quality and climate control matter as much as enrichment. In a study that provided straw through a foraging tower, the researchers tracked tail lesions across nursery and fattening periods. The most severe outbreak of tail biting was triggered not by a lack of enrichment but by a failure in the ventilation system. The resulting changes in air quality, including higher ammonia concentrations and sudden temperature swings, were strongly associated with tail lesions. In the nursery period, increased air velocity raised the chance of tail lesions; during fattening, ammonia concentration was the key environmental predictor.8PubMed Central. Provision of straw by a foraging tower -effect on tail biting in weaners and fattening pigs The takeaway is that even farms doing the right things on enrichment can still see outbreaks if the air in the barn goes bad.
A Genetic Component to Biting
Whether a pig bites or gets bitten is not purely a product of its environment. Genome-wide analyses have identified specific chromosomal regions associated with being a tail biter and separate regions associated with being a victim, suggesting that both tendencies have a heritable component.9PubMed. Identification of chromosomal locations associated with tail biting and being a victim of tail-biting behaviour in the domestic pig (Sus scrofa domesticus) Specific genes, such as PDK4, have been found to be expressed differently in biters, victims, and neutral pigs, opening the door to the idea that breeding programs could one day select against the behavior.10PubMed Central. Tail-Biting in Pigs: A Scoping Review
This is not just theoretical. Researchers have shown that selecting pigs for high “indirect genetic effects” on growth, essentially breeding for pigs whose presence helps their penmates grow better, produces animals that bite substantially less. Pigs from high-indirect-genetic-effect lines showed about 40% less aggressive biting, 27% less ear biting, and lower tail-damage scores compared to pigs from low lines. These genetic effects were additive to the benefits of straw bedding, meaning the two interventions stacked rather than overlapping.11PubMed Central. Indirect genetic effects for growth rate in domestic pigs alter aggressive and manipulative biting behaviour There is a troubling flip side, though: commercially desirable production traits like low backfat thickness have been negatively correlated with tail biting, suggesting that decades of selecting for lean, fast-growing pigs may have inadvertently bred animals more prone to harmful behavior.10PubMed Central. Tail-Biting in Pigs: A Scoping Review
What Happens to Bitten Pigs
The consequences of tail biting extend well beyond the tail itself. Once a wound opens, bacteria enter and can spread systemically, primarily through the veins to the lungs. Bitten pigs show higher rates of lung lesions, abscesses, joint infections, and bone infections.12PubMed Central. The Evidence for a Causal Link Between Disease and Damaging Behavior in Pigs These secondary infections are not just a welfare problem; they hit the farmer’s bottom line. Victimized pigs are more frequently sold at a discount and yield a lower dressing percentage at slaughter. Blood tests taken five days after tail injuries show elevated total serum protein and immunoglobulin concentrations, markers of active inflammation that foreshadow the carcass abscesses and trim losses that reduce market value.13PubMed Central. Effects of tail docking and tail biting on performance and welfare of growing-finishing pigs in a confinement housing system
True Cannibalism in Wild Boar
Farm-based tail biting is damaging and sometimes grisly, but the question of whether pigs literally eat each other finds its clearest answer in wild boar behavior around carcasses. A camera-trap study across multiple sites found that cannibalism, defined as wild boar feeding on dead conspecifics, was observed in about 10% of all recorded visits to carcass sites. The first direct contact with a carcass occurred on average 30 days after placement, and actual cannibalistic feeding began around 70 days later.14PubMed. Confirmed cannibalism in wild boar and its possible role in African swine fever transmission This has major implications for the spread of African swine fever, a devastating viral disease that can persist in carcasses for months.
The picture is not uniform across environments, however. A separate study in a hot, semiarid climate found no evidence of cannibalism among wild pigs visiting carcasses, with live pigs visiting only about a third of carcass sites before advanced decomposition set in.15PubMed Central. Behavior of Wild Pigs toward Conspecific Carcasses: Implications for Disease Transmission in a Hot, Semiarid Climate A third study, conducted in a European temperate setting, also found no intra-species scavenging of fresh carcasses, though piglets were observed chewing on bare bones once skeletonization was complete.16PubMed Central. Behaviour of free ranging wild boar towards their dead fellows: potential implications for the transmission of African swine fever These conflicting findings suggest that climate, habitat, food availability, and population density all influence whether wild pigs resort to eating their dead. In cooler climates where carcasses decompose slowly and virus persists longer, the window for cannibalistic contact may be wider.
The Tail Docking Dilemma
The most common industry response to tail biting has been to dock piglets’ tails shortly after birth, removing part of the target. In the European Union, routine tail docking is technically prohibited; legislation requires that farms first address housing and management conditions before resorting to docking. In practice, the vast majority of EU pigs are still docked because the steps producers must take before docking are not specified in detail, making enforcement difficult.17PubMed. Why are most EU pigs tail docked? Economic and ethical analysis of four pig housing and management scenarios in the light of EU legislation and animal welfare outcomes Producers, acting in their own economic interest, choose docking because the costs of an outbreak far exceed the cost of the procedure.
Raising pigs with intact tails is genuinely difficult even with best management practices. A Brazilian commercial trial comparing docked and undocked piglets found that tail biting was more common in undocked pigs across both nursery and finishing stages, with undocked pigs showing more severe lesions. By the finishing phase, tail biting was observed only in the undocked group. A contingency plan, enriching pens with sisal rope, successfully halted new cases after implementation, and overall productivity was not affected. But the study also revealed a behavioral cost: undocked piglets that needed the contingency plan showed higher fear responses during human interaction.18PubMed Central. Implications of No Tail Docking on Performance, Health, and Behavior of Pigs Raised Under Commercial Conditions in Brazil The researchers concluded that managing intact tails on commercial farms remains a significant welfare challenge, even when best practices are applied.
Docking itself carries welfare costs. Histopathological work on docked piglet tails found that traumatic neuromas, painful tangles of regenerating nerve fibers, begin forming within a month of the procedure and are still developing four months later.19PubMed Central. Histopathological Characterization of Tail Injury and Traumatic Neuroma Development after Tail Docking in Piglets The implication is that docked tail stumps may remain sensitive for an extended period, possibly throughout the pig’s life. This creates a painful irony: the procedure meant to protect pigs from biting pain may itself cause chronic discomfort.
Using Technology to Catch Outbreaks Early
One of the most promising developments in managing tail biting is automated monitoring. Pigs that are about to become victims of a biting outbreak tend to lower their tails before visible wounds appear, and researchers have been working to exploit this early warning sign with camera systems. A 3D machine-vision system designed to detect lowered tail posture achieved about 74% accuracy in distinguishing low tails from normal tails, with nearly 90% sensitivity in catching the low-tail signal.20PLOS ONE. Automatic early warning of tail biting in pigs: 3D cameras can detect lowered tail posture before an outbreak Commercial farm validation confirmed that increases in the proportion of low tails and reductions in high tails were associated with worsening tail injury severity and tail-length loss.21PLoS ONE. Changes in tail posture detected by a 3D machine vision system are associated with injury from damaging behaviours and ill health on commercial pig farms
Video-based deep learning is also being applied directly to detecting biting events. A system using a combined neural network architecture achieved about 71% accuracy in identifying tail-biting behavior from video footage, with improved performance when dimensionality reduction techniques were applied to the data.22PubMed Central. Automatic monitoring and detection of tail-biting behavior in groups of pigs using video-based deep learning methods These accuracies are not high enough to replace human observation entirely, but they could alert stockpeople to check specific pens before an outbreak spirals. On farms housing thousands of pigs, where daily visual inspection of every animal is impractical, even an imperfect automated alarm could prevent the kind of cascading damage that starts with one wounded tail and ends with dozens of infected carcasses at slaughter.