Guinea pigs are obligately social animals — solitary keeping causes genuine welfare harm that Switzerland has addressed through legal minimum social housing requirements.
Guinea pig solitary housing is a welfare failure that is both common and preventable. These are animals evolved to live in groups of 5-10, maintain constant social contact, and rely on companions for threat assessment and reassurance. A single guinea pig calling repeatedly in an empty hutch is expressing social need as clearly as any social mammal. The Swiss legal requirement for companion housing reflects the scientific consensus that solitary guinea pig keeping constitutes welfare harm. In the UK and most other jurisdictions, this remains a welfare recommendation rather than legal requirement — but one with strong scientific backing.