Why neutral ground does the heavy lifting
Guinea pigs are social animals who usually want company, but an established pig regards its cage as territory, and dropping a stranger into it invites a fight. Bonding therefore happens somewhere neither pig has lived: a large pen on a bathroom or kitchen floor, or a sectioned-off area of a room neither uses. Space matters as much as neutrality — the pair need room to retreat, circle and avoid each other while they work out who is who, so a pen several feet across is a better start than a carrier or a lap.
Setting the scene so there is nothing to fight over
Scatter the pen generously before the pigs go in: several piles of hay rather than one, vegetables spread in multiple spots, two water sources and hideys with two entrances each, so no pig can be cornered inside one. Single-entrance houses are the classic bonding trap, because a frightened pig backs into one and the other follows. Some hay or bedding carrying both pigs' scents can be mixed in. Put both pigs in at the same time, ideally at a calm point in the day, and settle in to supervise for hours, not minutes.
Reading the behaviour: noise is normal, blood is not
Expect a soundtrack: rumbling, teeth chattering, nose-offs, chasing, mounting and scent marking are all normal negotiation, and interrupting them just restarts the process later. Watch body language rather than noise — pigs who break off to eat, wander apart and come back are doing fine. Intervene calmly, with a towel or dustpan between them rather than bare hands, only for lunging bites that draw blood, a ball of locked fighting, or one pig trapped and screaming. If blood is drawn, separate and retry another day; repeated failures with boar pairs may mean a different pairing works better.
Pairing choices that stack the odds
Some combinations bond more smoothly than others. Two young sows usually settle quickly, a neutered boar with a sow is often straightforward, and two adult boars with established habits need the most space and patience. Age helps too: a calm adult can steady a nervous youngster, provided the size difference is not so great that the smaller pig gets bowled over in every chase. If you are choosing a companion from a rescue, ask whether the pigs can meet on neutral ground there first — a pair that has already eaten peacefully side by side once is a promising start to build on at home.
Moving in together and the days after
A pair that has eaten side by side, rested in the open and moved calmly around each other for a long session is ready for a shared cage — cleaned thoroughly, rearranged, and stocked with duplicate bowls, bottles and hideys so the old owner's scent claims are gone. Keep watching across the first week, since cage space is smaller than the pen and tensions can resurface at feeding time. Any pig with a bite wound that looks deep, or one who stops eating after a fight, should see a vet. Assigning each bonding session and the first week's checks to named people in KinsLe's Care Teams keeps supervision continuous, with completed sessions marked so everyone knows how far the pair has got.