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Social Structure and Group Dynamics
Pigs are highly social animals. Under free‑ranging conditions, they live in small groups of around eight, typically composed of:
- Three sows
- Their offspring
Adult boars are solitary and do not live in these family groups.
A social hierarchy forms once pigs reach maturity. Sows within the same group tend to synchronize their estrous cycles and share maternal responsibilities. Communal nesting is common: while some sows forage, one remains with the piglets.
In confinement, hierarchy forms extremely early—by one week of age. Piglets fight when new individuals are introduced, establishing dominance quickly.
Teat Order and Early Dominance
Piglets establish a teat rank within the first week of life:
- Dominant piglets secure the front teats, which produce more milk.
- These piglets grow faster and maintain higher status.
Once teat order is set, the hierarchy remains stable as long as the group composition does not change.
Dominance is influenced by:
- Body weight (heavier piglets are usually dominant)
- Genetics and experience (dominant sows tend to produce dominant offspring)
After hierarchy stabilizes, fighting decreases and is replaced by threats.
Weaning naturally occurs at 3–4 months, but in commercial systems it may occur as early as 3–4 weeks.
Reproductive Behavior
Sows normally have two estrous cycles per year and farrow twice.
Key reproductive influences:
- Pheromones and visual cues from boars stimulate estrus in gilts.
- After farrowing, weaning induces estrus in sows.
- Boars are used to detect females in heat.
Boar Courtship Behavior
Boars:
- Are highly vocal (produce a “courting song”)
- Show flehmen
- Nuzzle the sow’s head, shoulders, flank, and anogenital region
- Urinate repeatedly
- Produce thick, pheromone‑rich saliva
Boars raised without other pigs show poor sexual performance, highlighting the importance of social experience.
Communication
Pigs rely heavily on vocal and olfactory communication.
Vocal Communication:
Pigs produce around 20 distinct sounds:
- Grunts: common; used during rooting or in response to familiar stimuli
- Short grunt → excitement
- Long grunt → contact call, often linked to pleasure
- Squeals: arousal
- Screams: pain
- Barks: threat from dominant pigs
Visual Signals:
Visual communication is limited.
Tail position is a key indicator:
- Tightly curled tail → healthy, content pig
- Twitching tail → skin irritation
In commercial systems, tails are often docked to prevent tail biting.
Olfactory Communication:
Highly developed sense of smell:
- Sows detect lower concentrations of odors than boars.
- When a new pig is introduced, residents investigate by nosing.
- Pigs can establish social rank even when blindfolded, showing the importance of smell and sound.
Socialization and Development
Piglet socialization begins at:
- ~5 weeks with other pigs
- ~14 weeks with other species
Pigs aged 14–17 weeks are particularly sensitive; negative experiences during this period can delay sexual maturity and postpone first farrowing.
Under free‑range conditions, group living supports:
- Foraging
- Nursing
- Predator protection
- Establishment of a designated defecation area
In commercial systems, the most notable group behavior in newborns is huddling when cold.
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