In Switzerland, it's illegal to own just one of what?

In Switzerland, it is illegal to keep just one guinea pig because guinea pigs are social animals that need companionship from their own kind.

The rule comes from Switzerland’s animal-welfare regulations, which require social species to be housed in ways that support their behavioural needs. Guinea pigs naturally live in groups, communicate through sounds and body language, and can become stressed or isolated when kept alone. The law is therefore about keeping one guinea pig in social isolation, not about banning ownership of guinea pigs altogether.

A common mix-up is that Switzerland has a special “guinea-pig law.” In reality, the principle is part of a broader animal-welfare approach affecting other social species as well. Owners may keep more than one guinea pig, or arrange suitable contact with other guinea pigs; the important issue is that the animal should not be left socially alone.

The rule is also sometimes exaggerated online as meaning every Swiss household must permanently own two guinea pigs. The practical point is companionship and welfare, not a quirky required number of pets.