Guinea pigs are highly social animals that suffer significantly when housed alone, and appropriate pair or group housing is one of the most important welfare requirements for this species.
The welfare impact of solitary guinea pig housing is one of the most clearly documented cases of social deprivation in companion animal species. Guinea pigs in isolation show clear signs of distress including increased vocalization, reduced activity, and higher stress hormones. Switzerland's legal requirement for companionship reflects the scientific consensus. Yet solitary guinea pig housing remains common in the UK and elsewhere. Successful pair introductions require appropriate housing space, neutral territory for introduction, and monitoring of social dynamics. Same-sex pairs are straightforward when both animals are neutered; mixed-sex pairs require responsible reproductive management.