Guinea pigs are highly social animals that suffer significantly when kept alone, and many countries now require that they are kept in pairs or groups as a welfare standard.
The social nature of guinea pigs is fundamental to their wellbeing. In the wild they live in groups with complex social relationships; in captivity a solitary guinea pig has no outlet for affiliation, play, and social communication. Research clearly shows that isolated guinea pigs show higher cortisol levels and fewer positive social behaviours. The Swiss ban on solitary keeping reflects the strength of this evidence. Owners who lose one guinea pig to old age face the immediate welfare obligation to find a compatible companion, or to house their surviving animal with another guinea pig at a rescue centre.