Guinea Pig Nutrition

When we rolled out our food list, we sought feedback from the major guinea pig forums. One critique we heard is that there was not enough information about the overall planning of your guinea pig's diet. We included the feeding frequencies recommended by the diet expert at guineapigcages.com on our list, but those are just rough guidelines for that particular food. For instance, apples are a 1-2 times per week food, so you know that if you're feeding your guinea pigs apples every day, that's way too much. However, beyond not exceeding these feeding frequencies per food, how do you figure out exactly what to feed your guinea pig each day, and in what quantities?

Sources for Information
As it turns out, planning your guinea pigs' diet is a pretty complicated subject. For humans, there are calorie tables and nutrient tables, which spell how much food, and how much of each nutrient, a human should eat. We didn't find anything exactly like this for guinea pigs, although our research came across two academic/scientific sources that came closest:

• Juan M. Navia and Charles E. Hunt (1976), "Chapter 17: Nutrition, Nutritional Diseases, and Nutrition Research Applicatins," in Joseph E. Wagner & Patrick J. Manning, eds., The Biology of the Guinea Pig, Academic Press.
• Note that while there is a lot of good information in this source, it's rather old at this point. There may be newer studies than what they have cited. 
• National Research Council (1995), Nutrient Requirements of Laboratory Animals, Fourth Revised Edition.
• Regarding this source, Guinea Lynx points out the following:
• "Cons: some data is over 50 years old, other data is extrapolated from rat studies (the authors of this article encourage more research). Some of the specific diets recommended are only suitable for laboratory animals. The authors note the high protein, low fiber diet typical of a laboratory animal and mention that a cavy's diet in the wild consists of much more fiber and green vegetation."
• "A complete list of requirements is printed on page 104. Keep in mind, these are not daily requirements but instead the amounts of vitamins and minerals they recommend adding to a kilogram of food to provide proper nutrition. Your pig will only eat a fraction of a kilo per day."
• We would also call attention to the fact the table is called "Estimated Nutrient Requirements for Growth for Guinea Pigs," and their disclaimer on page 105: "The data are not sufficient to differentiate between adult maintenance requirements and growth, pregnancy, or lactation requirements; hence, estimates are provided for growth only." In other words, if you look at the humans tables for calories and nutrition, it differentiates based on children and adults, but this guinea pig food table can't do this.

We also looked at what other information we could find online, looking primarily at guineapigcages.com and Guinea Lynx. Using these sources of information, we want to share what we've found so far. Please note that this is just the best information we were able to find and understand, and should not be regarded as indisputable fact about what guinea pigs should eat! We may post on this topic again to revise these guidelines as we learn more. In addition, we recommend talking to your vet about your guinea pig's diet before making any major changes.

Keeping all this in mind, here is what we think you should know about planning your guinea pig's diet:

Diet Overview

• Water: Guinea pigs need 100 ml water per kilogram of body weight. (Give them unlimited access, of course. Don't just measure out this amount. However, do be concerned if they seem to be drinking significantly less than this amount.)
• Food: The diet expert at guineapigcages.com recommends: "50% hay, 40% veggies and 10% high quality pellets."
• Hay: Guinea pigs need unlimited access to quality grass hay. (If you need to know how much to buy, one person estimated that their guinea pigs "will eat/waste/use about 1/4-1/2 a pound of hay per day.") (That is, about 113-227 grams.)
• Veggies: about 1 cup of vegetables per day (including 2 servings of leafy greens and 1 serving of non-leafy green veggies daily, and fruits no more than 1-2 times per week in moderation). However, keep in mind that a cup is a measure of volume, and grams are a measure of weight. Since most of the nutritional requirement information we've found is by weight, it's probably a good idea to have a rough concept of what this converts to.
• According to Livestrong.com, for raw veggies, 1 cup converts to about 8 ounces, or about 227 grams. This seemed a bit high to us, however, so we decided to do an experiment to test this for ourselves. We put a measuring cup on a scale, and then filled it with various produce from the fridge (lettuce, zucchini, and gooseberries) to see how much it weighed when it reached the top. It weighed 100 grams, just to give you a rough idea of how much a cup of mixed fruits and veggies might weigh. 
• Note that the actual weight in a cup will vary by food. If you look at our food list, you'll see that most of the foods have a link to the USDA's National Nutrient Database for Standard Reference. This will let you know how many grams are in a cup of each food. It can be as low as 36 grams for a cup of collard greens and as high as 236 grams for a cup of passion fruit, but in general, the numbers mostly seemed to cluster around about 75 - 150 grams per cup. The juicy fruits and veggies tended to weigh more, while the leafy ones tended to weigh less. 
• Pellets: Oxbow Cavy Cuisine pellets are recommended. They recommend 1/8 of a cup of pellets daily. According to our humans' scale, this is about 20 grams. (This is also how much Guinea Lynx estimated a couple tablespoons of pellets to weigh.)

Key Nutritional Needs:

• Vitamin C: Adult guinea pigs need 10-30 mg of Vitamin C per kilogram of body weight per day. Remember, 1,000 grams = 1 kilogram, so unless you have an unusually large or small guinea pig, you'll probably want to feed your guinea pig around 25 mg per day. 
• Low vitamin C can cause a condition called scurvy. This is a very serious condition that can affect bones, blood vessels, adrenal glands, and more. If your guinea pig has scurvy, you'll want to increase their vitamin C intake to 50 mg/day.
• It's also possible to cause a condition called pseudo-scurvy if you give large doses of vitamin C (around 100+ mg per day), and then suddenly cut back to a smaller dose. This is a temporary condition, and nowhere near as serious of a concern as scurvy is. 
• Vitamin A: There is limited information currently available on guinea pig Vitamin A requirements. Some older studies suggested that 6.6 - 9.9 mg of vitamin A per kilogram of body weight per day is best. (Navia & Hunt, p. 241). However, the diet expert at guineapigcages.com starts warning about vitamin A being high on foods that have 316 mcg per 100 grams (equivalent to 0.316 mg, much lower than the Navia & Hunt information), so we're going to recommend avoiding feeding more than 300 mcg per day.
• Sugar: We haven't been able to find studies on how much sugar guinea pigs can have per day. However, on our favorite food chart, the diet expert at guineapigcages.com starts warning about high sugar levels for food with 3.8 grams per 100 gram servings. The highest sugar amount in an "almost daily" food is 2.4 grams per 100 gram servings. Therefore, until better information is available, we're going to recommend avoiding feeding more than about 3.8 grams of sugar per day on average, and try to aim for 2.4 grams or less. It might be okay to go a little over by feeding fruit as treats occasionally, but try not to go too far over, and not too frequently. 
• Calcium & Phosphorous: It is recommended that you keep the ratio of calcium to phosphorous to be between 1.5:1 and 2:1. Guinea Lynx has an Excel Spreadsheet you can use to calculator calcium-phosphorous ratios more easily. 
• Younger guinea pigs need calcium for bone growth. After six months, however, calcium intake should be lowered; keep to about a 0.3% level of calcium to prevent health issues.
• Based on a Guinea Lynx sample diet for avoiding stones, calcium from fruits and vegetables (not counting pellets) can range from 64 mg - 107 mg per pig per day, and phosphorous from fruits and vegetables (again, not counting pellets) can range from 39 mg - 71 mg per pig per day. 
• Magnesium: "the magnesium requirement is 1 to 3 g/kg diet, 1 g/kg diet being the minimum requirement" (National Research Council, p. 113)
• The National Research Council notes that: "Requirements for calcium, phosphorus, magnesium and potassium seem to reflect interactions among them." We have seen recommendations for the calcium-phosphorous ratio, but it's probably even more complicated when magnesium and potassium are taken into account.
• Oxalic Acid: Guinea pigs should eat no more than 50 mg per day.
• Too much oxalic acid can cause renal failure.

Other Nutritional Needs:

• Vitamin D: Some research suggests 500-750 IU of vitamin D per kilogram of body weight per day. (Navia & Hunt, p. 242)
• Vitamin E: The little evidence available on vitamin E suggests 1.5-6.0 mg per day (Navia & Hunt, p. 243).
• Thiamine: 2 mg per kilogram of body weight per day (Navia & Hunt, p. 244).
• Riboflavin: not determined (Navia & Hunt, p. 244).
• Niacin: about 10 mg per kilogram; also depends on quantity and quality of dietary protein (Navia & Hunt, p. 245).
• Pyridoxine (Vitamin B6): about 2-3 mg per kilogram of body weight per day (Navia & Hunt, p. 245).
• Folic Acid: young guinea pigs: 3-6 mg per kilogram of body weight per day, less for adults (Navia & Hunt, p. 245-6).
• Pantothenic acid: 20 mg per kilogram of body weight per day (source: Navia & Hunt, p. 246).
• Choline: 1.0-1.5 grams per kilogram of body weight per day (source: Navia & Hunt, p. 247).
• Other nutrients mentioned as important by the National Research Council, but difficult to convert into a daily requirement since they are expressed in amounts needed to be added to a kilogram of food, include (but are not limited to):
• Protein
• Essential fatty acids (n-6)
• Fiber
• Arginine
• Histidine
• Isoleucine
• Leucine
• Lysine
• Methionine
• Phenylalanine
• Threonine
• Tryptophan
• Valine

Planning Your Guinea Pig's Diet:

• Although a wide variety of nutritional requirements are mentioned above, in order to make your planning more manageable, we recommend focusing in on just a few of the key aspects that were identified by the guineapigcages.com diet expert: Sugar, Calcium, Phosphorous, Vitamin C, Vitamin A, Oxalic Acid, and the Calcium-Phosphorous Ratio. (It's probably safe to assume that if you feed a quality pellet and a varied diet, the rest will take care of itself.)
• Also keep in mind that cruciferous vegetables contain a substance called raffinose, which can make guinea pigs gassy and bloated if overfed. So try to limit the amount of these these, even if the numbers look good in these key indicators.
• Our food list provides links to sites with nutritional information; the USDA website is the preferred source for nutritional information since they are authoritative and relatively comprehensive.
• Oxalic acid information is missing from the USDA website, however. Sources where you can find oxalic acid information include the guineapigcages.com food chart, the Guinea Lynx oxalic acid chart, the USDA's Agriculture Handbook, LithoLink Corporation, and oxalicacidinfo.com.
• Trying to calculate the nutritional aspects of guinea pig pellets is very complicated. The standards for nutritional labeling are set by an organization called the AAFCO. Pet food labels use these standards, presenting information as "Guaranteed Analysis," which is very difficult to convert to the actual amount of nutrients in a given amount of pet food. For simplicity's sake, we just used the Guinea Lynx food chart generic guinea pig pellet numbers. We would have liked to have the actual numbers for the pellets we use, though.
• Using the guidelines suggested by our research, we decided to analyze an entry from a sample veggie menu from the diet expert at guineapigcages.com for nutritional content to see how well our draft guidelines matched up:

Our notes: 1. The gram amounts fall within our suggested range. 2. The vitamin C amounts are above our suggested minimum range, but is nowhere near the amount where pseudo-scurvy could be a problem. 3. The vitamin A amounts are under the suggested 300 mcg limit before pellets. 4. The sugar amounts are under our suggested maximum. 5. The calcium and phosphorous amounts are below our ranges for the fruit and vegetables portion of the diet.  However, being too high seems to be more of a concern than being too low, and the pellets will certainly add to this. Unfortunately, we only have generic pellet numbers. 6. The calcium-phosphorous ratio was off until pellets were factored in, which then put them within the ideal range. 7. The oxalic acid was a little high. The green beans were the biggest contributor to this. We think substituting one of the two green beans for another food that's lower in oxalic acid would have been a good idea. 8. Sources used in making this table included the USDA site, guineapigcages.com chart, and the Guinea Lynx chart (for pellet information).

• Once you've found a diet that's has sufficient amount of the good stuff and not too much of the bad stuff, don't just keep feeding your guinea pigs the same stuff over and over again. You'll want to maintain variety in your guinea pig's diet.
• It is better to have two meals a day for your guinea pigs rather than just one big meal. 

Final Thoughts
We want to emphasize again that we are not veterinarians, and this is by no means the last word on the subject. We are just presenting the best information we were able to find so far on how to plan your guinea pig's diet. Going forward, we would love to hear from veterinarians and other experts on guinea pig nutrition for feedback on these guidelines.

We would also like to see nutritional information on specific pellet products and types of hay presented in the same easy-to-read format as the food charts. It was sometimes unclear whether particular guidelines were applicable just to the veggies portion of our diets, or to the entire diet including hay and pellets. 

Once we feel more confident in our guidelines, perhaps we can do some posts with sample diets based on the guidelines, similar to the ones guineapigcages.com and Guinea Lynx made. Let us know in the comments section if you'd be interested in seeing this!

*Note: We did ask the humans for help with this post, since one of them has a Ph.D. and is a professional researcher, in case you were wondering. He didn't seem to mind, though. We rewarded him in snuggles.