Vocal and locomotor responses of piglets to social isolation and reunion.

Potentiation of infant isolation calls following a brief reunion with the mother is considered an index of filial bonding in altricial rodents. We investigated potentiation of isolation and reunion responses in 15-day-old unweaned domestic piglets (Sus scrofa domesticus). When piglets were re-isolated following a brief, comforting reunion with their mother and littermates in their home pen, they displayed a persistence (relative potentiation) of calling and jumping. In contrast, when re-isolated following a brief interaction with their mother or an unfamiliar sow in a familiar or unfamiliar location, or with littermates alone, calling rate and locomotion dropped. Subsequently, piglets spent more time near their mother's face if they had previously interacted with an unfamiliar sow rather than their mother, consistent with maternal recognition. Although we did not detect maternal potentiation as described in altricial rodents, filial attachment bonding was clearly evident in piglet responses, especially during reunions.