How to Feed a Guinea Pig
To feed a guinea pig, give it unlimited access to hay, which is important for digestive and dental health. Incorporate a cup of fresh veggies like celery, kale, or broccoli every day to ensure a balanced diet, and feed your guinea pig pellets sparingly, since eating too many can lead to obesity and dental problems. Serve the food on a durable ceramic tray and don't forget to provide access to fresh, clean water!
Feed your guinea pig hay. Guinea pigs love hay! They need it for digestive and dental health. Guinea pigs should have unlimited access to hay, which often means refilling a good-sized dish 3 to 5 times daily. Timothy hay is the best hay for all guinea pigs in general. They will happily eat it and play with it, and it's healthy for pigs of all ages. Meadow hay, bluegrass, and orchard grass are also good choices, but not all guinea pigs like them. Alfalfa hay contains a lot of calcium, so is inappropriate for older pigs except as an occasional treat. Even if your guinea pig loves alfalfa hay, use it as a treat, not part of the normal diet. However, pregnant and nursing sows and guinea pigs under six months can eat more of it (in addition to Timothy). Look for hay that is green and soft, as yellow and hard hay means it's straw. Hay can be purchased from pet stores, but it's usually very expensive and has sat a long time. You can often order hay directly from a local farm, online, or through your exotics veterinarian, which is often cheaper and higher quality. Feed your guinea pig about a cup of fresh vegetables daily. The key is to provide it with a lot of variety so that it gets a balanced diet. Veggies that are good for guinea pigs include celery, off-the-vine tomatoes, cucumber, corn (and corn husks), and bell pepper.. Other vegetables such as beetroot, parsley, and forages such as clover or dandelion leaves (wash them first), should be given on occasion. Do not give your guinea pigs spoiled or wilted vegetables. Remember, don't feed them any vegetables in poor enough shape that you wouldn't eat them. Be careful of calcium intake. Too much calcium can result in bladder stones, so feed high-calcium foods like kale, spinach, and parsley sparingly. Acidic vegetables, such as tomatoes, can cause sores, therefore these should also be limited to only 1-2 times a week. Feed your guinea pig pellets. Be aware pellets are high energy, and eating too many can lead to obesity and dental problems. Feed only a 1/8 cup per day to supplement the other parts of its diet. Look for pellets that are supplemented with vitamin C. This is an important nutrient that guinea pigs need in their diet. Avoid providing feeds with sugar, seeds, or colorful pieces ("muesli feed") as these are unhealthy and your guinea pig may start eating only them. Also, make sure the pellets are Timothy, not alfalfa-based unless they're for nursing/pregnant sows or guinea pigs under 6 months. Only use pellets designed for guinea pigs. Pellets for rabbits or other rodents aren't suitable for guinea pigs as they contain different quantities of essential vitamins and nutrients. Make sure your guinea pig is getting enough vitamin-C. Guinea pigs are one of the very few mammals (along with humans) who can't make their own vitamin C, so they need to get it from their food. They need 10 - 30 mg of Vitamin C daily. Bell peppers are an excellent source of it. Guinea Pigs are highly prone to getting scurvy, which is a disease caused by low levels of Vitamin C. You can supplement your guinea pig's vitamin-c intake if necessary, but as long as you're feeding good pellets and fresh bell pepper, your guinea pig(s) will probably get enough. Putting vitamin-c into your guinea pig's water is not recommended. Adding vitamin C to the water can cause a guinea pig to stop drinking water if they don't like the taste and most of the vitamin C breaks down within half an hour, anyway. Avoid giving guinea pigs foods that are bad for them. This includes large amounts of fruits with high sugar contents (they should only be given in moderation) and any starchy vegetables, such as potatoes. High-calcium foods can be fed in small quantities. Vegetables to avoid feeding your guinea pigs include iceberg lettuce, potatoes, avocado, and cabbage. Feed fruit in small quantities. Not only does fruit have high sugar content, but it may also have low calcium to phosphorus ratio, which could lead to bladder problems and possible diarrhea. This is true in fruits such as raisins. Avoid giving your guinea pig citrus fruits altogether; the acid can irritate their mouths. Guinea pigs are herbivores. This means that they should not be fed any meat or dairy products. Avoid commercial guinea pig treats. These are a waste of money and are not good for your pet. Your guinea pig would like a treat of a piece of apple or carrot as much as a processed treat. Feed a balanced diet, instead of supplementing with multivitamins or salt wheels. These kind of additions to your pet's diet are not necessary if you take the time to feed your guinea pig well. If you do need to feed your guinea pig supplements, consider giving it vet-approved supplements that are high in fiber. Control the number of veggies you give your guinea pig. Guinea pigs chew instinctively and will eat as much as you feed them throughout the day. Watch how much you give them and stick to a balanced diet. Explain this gently to small kids who own guinea pigs so that they do not overfeed their pets. This only applies to vegetables. Hay must be available at all times Serve food in ceramic dishes. Guinea pigs will chew on anything they can get their teeth on, including their food dishes. Opt for a heavy ceramic dish that can't be easily be overturned and won't be easily destroyed. Keep food fresh. Uneaten food should be removed promptly, within one day. Guinea pigs can be picky eaters, so keeping food in their cage longer will probably not make it any more appealing to them. If they have avoided it for a whole day, they are probably never going to eat it and it will just simply become a mess in their cage. Adjust food quantities if the guinea pig becomes underweight or overweight. The amount of food a guinea pig will need depends on its age, its lifestyle, and its general health. This means that the amount of food you feed your guinea pig may need to change over time to keep them in good health. Provide fresh water at all times. Place a water bottle in your guinea pig's cage, so that it can access clean water at any time. Don't allow the water bottle to become empty. If a guinea pig doesn't have access to water it can become very ill. The best water bottles are designed for guinea pigs or rabbits and have a metal ball in the spout. Do not buy ones with springs; guinea pigs aren't strong enough to get the water from these. If your guinea pigs live in a pen outside, make sure that the water doesn't freeze during the winter. If it does, it is much too cold for your guinea pigs to be outside, anyway! Clean the water bottle nozzle frequently with a Q-tip to keep it free of obstructions and food residue. Clean the water bottle itself by placing uncooked rice and a little water in the bottle, and then shaking it vigorously. The rice will dislodge any greenish (algae) build-up. If algae is growing in it (even if it was removed by the rice), fill the bottle with white vinegar to kill it. Make sure to rinse it well before putting it back in the cage. Let your guinea pig graze occasionally. If you have a lawn that you know does not have chemicals on it and is not used by other pets for urinating and defecating, you can let your guinea pig graze on it. Get a fully enclosed outdoor run and let your guinea pig roam around in it during warm weather. Just make sure there is no breeze and the temperatures are between 60 and 75 degrees Fahrenheit (15-24 degrees Celsius). Only allow them outdoors in a run when supervised. While some guinea pigs do live in pens outdoors, they should not be left in an open-air pen without supervision. This could leave them exposed to predators or allow them to escape. Predatory birds may be more common than you realize and won't hesitate to attack a guinea pig. Make sure they have a dark place for them to hide in from the sun, or if something scares them. Move the run around from day-to-day. Guinea pigs will keep your lawn nice and short, and they fertilize it too. 
Feed your guinea pig hay. Feed your guinea pig about a cup of fresh vegetables daily. Feed your guinea pig pellets. Make sure your guinea pig is getting enough vitamin-C. Avoid giving guinea pigs foods that are bad for them. Avoid commercial guinea pig treats. Feed a balanced diet, instead of supplementing with multivitamins or salt wheels. Control the number of veggies you give your guinea pig. Serve food in ceramic dishes. Keep food fresh. Adjust food quantities if the guinea pig becomes underweight or overweight. Provide fresh water at all times. Let your guinea pig graze occasionally. 