Part of our goal and vision for our rescue is not only to re home and save unwanted pets, but to educate the public on proper care, housing and veterinary requirements for small animals.
Guinea pigs should only be fed Young Guinea Pig Food until they are about 6 months old. Around 5.5 months old, you can start transitioning them to an adult food by mixing in a little bit each day, and slowly increasing the amount of adult food, and decreasing the amount of young food that they get. By the 6 month mark, they can be taken off of the Young Guinea Pig food. Young guinea pig food tends to be high in alfalfa content, which growing guinea pigs need, but only until a certain point in their lives (much like human babies need mom's milk and/or formula).
Which leads me to the next point - kibble. As with all small animals, a high quality kibble is always recommended. We prefer and advocate Oxbow, however we realize that that's not always an option for people. If you are unable to go with Oxbow, you will want to go to an adult TIMOTHY based kibble. Martin Little Friends brand is good, just ensure you are buying the Timothy based kibbles. They are a few dollars more per bag, but will save you potentially thousands of dollars in vet bills. Calcium can (and will) build up in the piggies, including in their organs, which can lead to bladder stones, infections, or much worse.
Kibble Amounts: no more than 1/8 of a cup of kibble per pig - twice a day (so 1/4 cup total per pig, split over 2 feedings). Only a mere 5% of their diet should be kibble and treats.
Hay: Fresh timothy hay should be fed at ALL times. This is critical to their overall health, as well as the health of their teeth. 80% of their diet should consist of a good quality timothy hay. Alfalfa hay should rarely be given past 6 months old, for the same reasons you don't give them alfalfa based kibbles past that point. They don't need it - and it can do more harm than good.
The remaining 15% of a guinea pig's diet should be fresh, piggie safe veggies. These include dark leafy greens (romaine and leaf lettuce - NEVER feed a guinea pig iceberg lettuce!), herbs, green peppers, and a wide variety of other things. We have a list of ones that we recommend that we are happy to hand out to everyone for educational purposes. Things like Carrots and fruits should be fed VERY sparingly, as they are extremely high in sugar, which is not great for the piggies.
This is just the basic information regarding proper diet. There is LOTS to learn, and we understand that it can be a bit overwhelming! If you have any questions about your piggies (even if you didn't adopt them from us!), please don't hesitate to get in touch with us - and we will be happy to help!