Pigs sometimes kill their own newborns, a behavior known in farming as “savaging.” It happens most often in first-time mothers, with 5% to 15% of sows giving birth for the first time attacking or killing their piglets. The behavior has roots in hormonal shifts, pain, stress, and in wild populations, evolutionary pressures that once gave infanticidal animals a survival advantage.
What Savaging Looks Like
Savaging ranges from a sow snapping at her piglets to actively biting and killing them shortly after birth. It typically happens within the first hours or days of life, often during or immediately after delivery. The behavior is distinct from the far more common cause of piglet death: accidental crushing. In free-farrowing systems, crushing accounts for about 83% of liveborn piglet deaths in the first five days, with rates around 11.8%. Savaging is rarer but more deliberate, and understanding the difference matters because the causes and solutions are entirely different.
Hormones and the Pain of Birth
The most consistent trigger for savaging is the hormonal storm surrounding birth. Estrogen, progesterone, and stress hormones shift dramatically as a sow goes into labor, and these changes are supposed to activate maternal bonding. In some sows, particularly first-time mothers whose bodies have never navigated this process, the hormonal cascade goes wrong. Instead of triggering nurturing behavior, it produces fear or aggression toward the piglets.
Pain plays a major role. Farrowing is physically demanding, and sows experiencing difficult or prolonged deliveries are more likely to lash out. The combination of pain, unfamiliar sensations, and the sudden appearance of squealing piglets can overwhelm a sow that has no prior experience with motherhood. By the second or third litter, most sows have adjusted, which is why savaging rates drop sharply after the first birth.
Stress and Confinement
The environment a sow gives birth in has a powerful effect on her behavior. Farrowing crates, the narrow metal enclosures used on many commercial farms, restrict a sow’s movement so severely that she can’t turn around. Research comparing farrowing systems found that crated sows showed significantly more abnormal behaviors like repetitive chewing motions and biting at the bars of their enclosures. These are signs of chronic stress.
Sows are naturally driven to build nests before giving birth. In the wild or in open pens, a pregnant sow will spend hours gathering material, pawing at the ground, and arranging bedding. Farrowing crates make this impossible. When a sow can’t perform nesting behavior, her stress hormones stay elevated through delivery, and that stress can translate into aggression toward her newborns. Studies found that sows housed in more spacious, enriched environments with nesting materials showed fewer abnormal behaviors, and their piglets were less aggressive too.
Noise, unfamiliar handlers, and proximity to other stressed animals all compound the problem. A sow that might have been a perfectly calm mother in a quiet, spacious setting can become dangerous in a loud, cramped farrowing house.
Hunger and Nutritional Stress
Breeding sows are often fed restricted diets during pregnancy to optimize reproductive performance, which can leave them chronically hungry. That hunger drives aggression. Hungry sows confined in gestation stalls develop repetitive stress behaviors like bar biting and sham chewing, and in group housing, underfed sows fight more and sustain more injuries. A sow that enters the farrowing period already stressed and aggressive from months of hunger is at higher risk of turning that aggression on her piglets.
Why Wild Boars Do It Too
Savaging isn’t purely a product of modern farming. Wild boars also kill piglets, though the dynamics are different. Research on enclosed European wild boar populations documented extensive infanticide and identified four evolutionary explanations for why it may persist as a behavior.
The first is simple exploitation: a piglet is a food source, and a hungry or competing sow may treat it as one. The second is resource competition. Killing another sow’s offspring means more food, space, and nest sites for the killer’s own young. Third, a mother may sometimes improve her surviving piglets’ chances by reducing the litter to a size she can actually feed, a strategy called parental manipulation. Fourth, males occasionally kill piglets to bring a female back into heat sooner, creating a new mating opportunity.
Wild sows have developed counter-strategies over time. They tend to synchronize their birthing so that many litters arrive at once, making it harder for any single infanticidal animal to target them all. They also isolate themselves in carefully chosen nest sites before giving birth, putting distance between themselves and potential threats. These instincts persist in domestic pigs, which is part of why denying a sow the ability to nest and isolate herself causes so much behavioral disruption.
Genetics and Breed Differences
Some sows are genetically more prone to aggression than others. Studies in Large White sows estimated that aggressive traits have a moderate heritability, ranging from about 11% to 28%. That means a meaningful portion of the variation in aggression between individual sows comes down to genetics rather than environment alone. Researchers have found that it’s theoretically possible to breed for calmer maternal behavior, selecting sows that show less aggression and better piglet-rearing performance to produce future generations of more reliable mothers.
Interestingly, sows that were more aggressive toward other sows during pregnancy were actually less likely to be aggressive toward their piglets. The relationship between social dominance and maternal aggression appears to be inversely linked, suggesting these are separate behavioral systems rather than a single “aggressive personality.”
How Farmers Reduce the Risk
Prevention starts with recognizing which sows are at highest risk. First-time mothers get the closest monitoring, especially during and immediately after delivery. Many farmers stay present for the entire farrowing process with gilts (young sows giving birth for the first time) so they can intervene quickly if aggression starts. Removing piglets temporarily and reintroducing them gradually sometimes allows the sow’s maternal instincts to catch up.
Environmental changes make a significant difference. Providing nesting materials like straw, keeping the farrowing area quiet, minimizing handling by unfamiliar people, and giving sows more space all reduce stress. Some operations have moved toward free-farrowing pens that give sows room to move and nest while still providing a protected area where piglets can retreat away from the mother.
Feeding strategies also help. Ensuring sows aren’t chronically hungry during gestation, either through higher-fiber diets that increase satiety or through more generous feeding programs, reduces baseline aggression going into the farrowing period. On the genetic side, breeding programs increasingly track maternal behavior traits alongside growth and litter size, gradually shifting herds toward calmer, more attentive mothers.