Q: Sometimes we like to let our two-year-old guinea pig run around the backyard (supervised). Is it OK for him to eat grass? How cold is too cold to let him out?
– Bradley Wu, Vancouver

A: Domestic guinea pigs came from South America, where their ancestors roamed the (presumably chilly) slopes of the Andes. If you are comfortable outside without a coat, it's warm enough for him. Keep him off wet grass and provide some shade.

Guinea pigs' digestive tracts are designed for lots of forage, so not only is it OK for him to eat grass, but you can also let him eat as much as he likes. A good source of nutrition, fresh grass does come at a price: he may need regular deworming since soil and grass can contain parasite eggs.

Feeding him concentrated rations, such as pellets, can lead to health problems, so – even in winter – most of his food should be roughage, such as good-quality timothy hay and vegetables. And remember that guinea pigs are one of the few species (besides us) that require daily vitamin C, so they do need supplements.

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