Pigs can exhibit behaviors resulting in the consumption of their own kind, known as cannibalism in animal husbandry. This behavior is usually not a predatory act driven by hunger, but rather a behavioral disorder starting with aggression or redirected vices. In swine, cannibalism often follows a breakdown of social order or an escalation of aggressive habits, such as biting pen mates. The consumption of tissue occurs because pigs are naturally attracted to the sight and smell of blood from an initial injury. This problem is driven by a combination of environmental, physiological, and management stressors.
Forms of Aggression and Cannibalism in Swine
The most recognized form of this disorder in growing and finishing pigs is tail biting, which begins as exploratory behavior and escalates into a destructive vice. Pigs are curious animals that use their mouths to investigate, and in barren environments, this oral activity is redirected toward pen mates’ tails. Once blood is drawn, the scent and taste trigger a chain reaction, leading to obsessive biting and tissue consumption. Other localized forms of aggression that can evolve into cannibalism include ear biting and flank biting, where the initial minor injury attracts further attention from the group.
Another distinct form of aggression is “savaging,” where a mother attacks and kills her newborn piglets, sometimes including consumption. This infanticide is most common in young, first-time mothers (gilts) and typically happens within the first two days after farrowing. Savaging is often linked to the sow’s nervousness, pain during birth, or an inability to establish a proper maternal bond. While aggression is the primary concern, the consumption of the deceased piglet can occur in extreme cases, representing a severe breakdown of maternal behavior.
Environmental and Management Stressors
Aggressive behavior is significantly driven by the physical environment and management practices. Overcrowding, or high stocking density, increases competition for limited resources like feeder space and water access, elevating stress and frustration. When pigs constantly compete or walk over one another, the potential for conflict rises substantially. Also, mixing unfamiliar animals to form new social groups disrupts the natural hierarchy and can provoke “sudden-forceful” biting as pigs establish dominance.
The physical climate of the housing facility also plays a large part in the overall stress experienced by the animals. Inadequate ventilation leads to poor air quality, including high levels of noxious gases like ammonia, dust, and excessive humidity, which act as chronic stressors. Temperature fluctuations, especially heat stress, increase irritability because pigs cannot sweat effectively and are sensitive to uncomfortable thermal conditions. These poor conditions increase the group’s general activity and anxiety, lowering the threshold for aggressive outbursts.
A lack of environmental enrichment is a major stressor, causing boredom and frustrated foraging instincts in intelligent pigs. Pigs are naturally motivated to root, chew, and explore. When housed in barren pens without materials like straw, chains, or other manipulable objects, they redirect this behavior toward pen mates. This frustrated motivation is a precursor to the obsessive form of tail biting, as the animal seeks an outlet for its innate behavioral needs.
Dietary and Physiological Factors
The composition of a pig’s diet and its physiological state are closely linked to aggressive vices. Deficiencies in protein or specific amino acids can trigger behavioral issues as animals search for alternative protein sources. For example, a diet low in the amino acid tryptophan has been linked to increased aggression and tail biting. Tryptophan is a precursor to the neurotransmitter serotonin, which regulates mood and stress response; thus, a deficiency increases irritability and anxiety.
Specific mineral imbalances are also known contributors, with a lack of salt (sodium chloride) being a common trigger for oral vices. Sodium deficiency increases the pig’s motivation to lick or chew objects and increases the preference for the taste of blood, accelerating the progression to consumption. Also, insufficient dietary fiber reduces gut fill and satiety, leaving pigs hungry and increasing their motivation to chew.
Low fiber and finely ground feed particles can contribute to gastrointestinal discomfort, such as stomach ulcers, which are a source of chronic stress. This internal discomfort increases the pig’s motivation to chew and forage excessively, which may be redirected toward the tails or ears of other pigs. Unpredictable or irregular feeding schedules, including running out of feed, also generate high levels of frustration and anxiety, making the herd more prone to aggressive outbreaks.
Mitigation and Behavioral Management
Addressing the problem requires a comprehensive approach targeting the root causes identified in the environment and diet. The primary management strategy is to satisfy the pig’s innate need for exploration and chewing by providing environmental enrichment. Supplying manipulable materials such as straw, hay, chains, or wooden blocks allows pigs to redirect their oral fixations away from pen mates. To be effective, enrichment must be continually available, edible, and destructible.
Optimizing the physical environment is another important step, involving adjustments to stocking density to reduce competition and stress. Ensuring all pigs have ample space to rest and easy access to feed and water minimizes the potential for resource-based aggression. Maintaining consistent air quality and stable temperatures within the pig’s thermal comfort zone reduces physiological stress and overall irritability.
Dietary interventions involve ensuring that feed is balanced and meets the pig’s nutritional requirements for protein, amino acids, and minerals, especially sodium. Increasing the fiber content in the feed enhances satiety and reduces the motivation to forage destructively. As a prophylactic measure, some farms still employ tail docking, which reduces the target for biting and the economic impact of injuries, though this practice is increasingly regulated and viewed as a last-resort management tool.