Quick answer
Build a guinea pig’s diet in this order: unlimited grass hay first, then a measured daily portion of vitamin C fortified guinea pig pellets, then fresh vitamin C rich vegetables every single day. For adults, our top pellet is Oxbow Essentials Adult Guinea Pig Food, a timothy based formula with added stabilized vitamin C. Kaytee Forti-Diet Pro Health is the widely stocked value option, and Small Pet Select Guinea Pig Food Pellets is a clean three ingredient upgrade. Pair any of them with quality timothy hay such as Oxbow Western Timothy or Small Pet Select hay, plus daily veg like bell pepper.
Why vitamin C and hay matter
Guinea pigs cannot make their own vitamin C, so they must get it from food every day or they can develop scurvy, a painful deficiency that causes stiff joints, poor coat and bleeding gums. That single fact shapes the whole diet: you need a reliable daily vitamin C source. Hay is the other pillar. Unlimited grass hay makes up the bulk of the diet, keeps the gut moving and wears down teeth that grow continuously for life. Pellets and veg support hay, they never replace it.
What to look for
Choose a timothy or grass hay based pellet with timothy listed first, not alfalfa, for adult pigs. Confirm added stabilized vitamin C (often ascorbyl monophosphate), which holds potency longer than plain ascorbic acid. Pick plain, uniform pellets with no seeds, dried fruit or colored bits that invite selective eating. Check the bag date and buy fresh, because vitamin C degrades over the weeks after milling. Keep calcium moderate for adult males and older females to reduce bladder stone risk.
How we chose
We compared labels, ingredient decks and guaranteed analysis across widely available guinea pig pellets, checking the first ingredient, the vitamin C form, fiber level and calcium load. We favored timothy first formulas with a clearly stated stabilized vitamin C source, honest ingredient lists and reliable stock. We did not run feeding-data reviews or make health claims. Our picks reflect published specifications, ingredient quality and long term availability so you can rebuy the same food consistently. We also weighted bag sizes you can finish while the vitamin C is still fresh, since a smaller pack that stays potent beats a bulk bag that fades.
What to avoid
Do not feed rabbit food or generic rodent food to guinea pigs. These lack added vitamin C and can contain ingredients that are wrong for a pig, so a guinea pig eating rabbit pellets can slide toward deficiency. Skip muesli style mixes, sugary treats and yogurt drops. Do not rely on vitamin C drops in the water bottle, because the vitamin degrades fast in water and the altered taste can put a pig off drinking. Get most vitamin C from fresh dated pellets and daily veg instead. Also skip iceberg lettuce, which is mostly water and low in nutrients, and never make sudden diet swaps, since a guinea pig gut needs a slow transition of about a week to avoid soft stool.
