Cannibalism, or savaging, occurs in pigs under specific conditions, often driven by intense stress or a misdirection of natural behavior. This behavior is a significant concern in swine management because it signals a breakdown in welfare or environmental stability. Understanding it requires distinguishing between different types of aggression and the circumstances that cause a pig to consume a conspecific. The phenomenon is caused by a combination of biological, nutritional, and environmental factors.
Categorizing the Behavior in Swine
Cannibalism in swine covers two distinct behavioral patterns: maternal aggression and aggressive group consumption. The most common form is maternal cannibalism, or “savaging,” where a sow or gilt attacks and consumes her own newborn piglets, usually within 48 hours after farrowing. This behavior is most frequently seen in first-time mothers (gilts) and accounts for a significant portion of early piglet mortality.
The second category is aggressive cannibalism, which escalates from redirected exploratory behaviors like tail, ear, or flank biting. This often begins as mild oral manipulation of a pen mate’s tail, a way for the pig to explore when it lacks proper stimulation. Once the skin is broken and blood is drawn, the situation escalates rapidly. The taste and smell of blood, which contains appealing components like salt and protein, attract other pigs to continue biting.
It is important to distinguish between true cannibalism (killing a conspecific for consumption) and necrophagy (consuming an animal that is already dead). Much of the consumption observed in group-housed pigs is technically necrophagy, where pigs consume a group member that died from injury, illness, or crushing. However, aggressive behaviors leading to severe injury, such as tail-biting, can quickly transition into a fatal attack and consumption, blurring this distinction.
Underlying Biological and Environmental Stressors
The causes of cannibalistic behavior are multifactorial, stemming from nutritional deficits and psychological stress. A major driver is the pig’s strong, natural motivation to forage and explore using its snout and mouth. When this behavior cannot be performed on suitable materials, the pig redirects its oral manipulation toward the tails and ears of its pen mates, which can escalate to a damaging level.
Nutritional Deficiencies
Imbalances in the diet contribute to abnormal feeding behaviors. Deficiencies in minerals, such as sodium or iron, intensify the pig’s attraction to the taste of blood, which is rich in these compounds. A lack of crude fiber is another factor, as fiber promotes gut health and provides satiety, reducing the motivation for abnormal chewing. Furthermore, the sudden drop in feed intake imposed on sows before farrowing can induce hunger and agitation, triggering maternal savaging.
Environmental Stress and Density
The physical environment powerfully influences porcine aggression. High stocking density, which restricts space, increases social friction and competition for resources like feed and water, raising stress levels. Barren housing conditions, lacking materials for rooting and chewing, lead to boredom and frustration. This compels pigs to seek alternative outlets for their exploratory drive, often resulting in tail-biting. Housing systems using fully slatted floors, which prevent bedding provision, show a higher frequency of aggressive behavior compared to straw-bedded areas.
Physiological Drivers
Maternal savaging is linked to hormonal shifts occurring during and after farrowing. Research suggests that an imbalance in steroid hormones, specifically high levels of estradiol relative to progesterone near birth, may contribute to aggressive maternal behavior. Stress hormones, such as cortisol, are also implicated in aggression, as chronic stress lowers the threshold for aggressive responses. While no single gene has been identified, some commercial swine lines are considered more prone to aggression, suggesting a genetic predisposition interacting with environmental factors.
Scientific Approaches to Prevention
Strategies for mitigating cannibalism focus on addressing the underlying environmental and nutritional deficiencies that trigger the behavior. Since the problem is multifactorial, prevention requires a comprehensive approach managing the animals’ mental state and physical needs. Recognizing that aggression is a symptom of an unmet need allows managers to implement changes that redirect the pig’s natural motivations into acceptable outlets.
Dietary Adjustments
Feed formulation is a primary tool for prevention, ensuring the diet is complete and balanced to eliminate nutritional cravings. Supplementing the diet with sodium chloride helps satisfy mineral deficits and reduces the attraction to the salty taste of blood. Increasing the fiber content provides a feeling of fullness and encourages healthy gut activity, which helps calm the animals. For acute outbreaks, including amino acids like tryptophan and highly digestible magnesium sources has been shown to reduce aggressive episodes.
Environmental Enrichment
Providing appropriate environmental enrichment is an effective preventative measure designed to satisfy the pigs’ natural exploratory and foraging instincts. Optimal enrichment materials are chewable, destructible, and ideally ingestible, such as straw, hay, or wood blocks. Providing at least 200 grams of straw per pig per day is recommended to fully engage their manipulative behaviors. Consistent enrichment successfully diverts the pig’s attention away from pen mates, reducing the initial exploratory biting that leads to escalation.
Early Detection and Segregation
Careful observation allows for intervention before an outbreak becomes a cannibalistic event. Managers look for early warning signs, such as pigs with tucked down or reddened tails, which signals the beginning of a problem. The immediate removal and segregation of the initial aggressor or the victim is a common technique to stop the cycle of attraction and escalation. For maternal savaging, careful management of gilts, including providing nesting material and a sufficient period to settle into the farrowing environment before birth, is a preventive step.