Guinea pigs share the essentials with rabbits: they're herbivores with continuous digestion and teeth that never stop growing, so hay is also the base of their diet. But they have one particular trait worth knowing from the start.
Why hay comes first for guinea pigs too
Just as with rabbits, hay gives guinea pigs the long fiber that keeps their digestive transit running and the wear their continuously growing teeth need. It should be available at all times throughout the day, and make up most of what they eat.
Vitamin C, the important detail
The key difference is that guinea pigs can't make their own vitamin C, so they have to get it from their diet. Hay isn't a significant source of this vitamin, so it mainly comes from suitable vegetables rich in vitamin C and, when a vet recommends it, a supplement. Hay remains the base; vitamin C is the one extra a guinea pig can't do without.
How much and what hay
For an adult guinea pig, the right choice is a grass meadow hay, available at all times, such as mountain meadow hay. Alfalfa, richer in calcium and protein, is reserved for specific cases such as pups or pregnancy, and always best under veterinary guidance.
Mountain meadow hay for guinea pigs
A high-mountain meadow hay, with many different species, gives a guinea pig variety and fiber in the same format as a rabbit. It's the same hay; only the animal eating it changes.
