Guinea pigs are highly social animals that suffer from isolation. In Switzerland it is illegal to keep a single guinea pig, recognizing their social needs as a welfare essential.
Guinea pig welfare depends fundamentally on social companionship. These prey animals evolved in social groups and use contact, vocalization, and group vigilance for security. Keeping guinea pigs alone causes chronic stress that affects both behavior and physiology. Providing compatible social companions is the single most important welfare improvement for guinea pig owners.