The guinea pig plays an important role in the folk culture of many Indigenous South American groups, especially as a food source, but also in folk medicine and in community religious ceremonies. See Guinea Pigs as Food in Wikipedia.
They make great compost with pellets which - like other herbivore faeces - are enjoyed by chickens, so their wastes can be further cycled in a chicken tractor setting. Good page here about basic needs.
See some more resources about this in the spanish page of this e-book, also of larger-scale breeding programmes - not permacultural but easily adaptable to be a lot more sustainable.