A guinea pig diet shouldn’t consist solely of pellets or seed mix. These cute pets also need roughage (fibers) in their diet and a well-known source of fibers is hay. But can guinea pigs also eat fresh grass, or should grass be avoided as a food source?

Guinea pigs can eat grass without a problem. You should give fresh or dried grass daily as much as they want. Grass helps the digestive systems of your guinea pig to function properly. Although most grass is safe for guinea pigs, preferred grass species are Timothy, orchard grass, and wheat grass.

Although grass is healthy and necessary for most guinea pigs, there are some precautions you’ll need to take to prevent your guinea pigs from getting sick. However, considering these precautions, grass’s benefits will keep your guinea pig healthy and happy.

Do Wild Guinea Pigs Eat Grass?

The guinea pigs we keep as pets don’t exist in the wild. Guinea pigs are likely a hybrid of different species of cavy that originate from South America. Their wild ancestors used to live in a grassland habitat. As such wild guinea pigs would eat grass. Grass was a large part of their diet and provided the necessary fibers.[1]https://en.wikipedia.org/wiki/Guinea_pig

Benefits of Eating Grass

Guinea pigs are strict herbivores, meaning they only consume plant matter. Their diet consists of vegetables, fruit, and also grasses. Grasses and hay should be the largest percentage of a guinea pig’s diet (between 80 and 90%).[2]https://www.pdsa.org.uk/pet-help-and-advice/looking-after-your-pet/small-pets/your-guinea-pig-s-diet

High fiber content

Guinea pigs need enough fibers in their diet. Hay and grass are excellent sources of fibers. In the table below, you can find the percentages of fiber in different grass species that can be found in pet stores or online. You can also find the percentages for common garden grass species.[3]See for these and other grasses: https://www.feedipedia.org

Grass speciesFiber percentage
Timothy grass31.8%
Bermuda grass31.3%
Orchard grass32.0%
Oat grass34.0%
Buffalo grass30.2%
Wheatgrass24.1%
Centipede grass34.2%
Ryegrass28.8%
Fiber percentage in grasses

Calcium

Calcium is a mineral that is essential for most animals. The mineral is necessary for several bodily functions and is needed to build strong bones and teeth. Since guinea pigs’ teeth never stop growing, it’s very important that your guinea pigs get enough calcium in their diet. However, you also don’t want to feed too much calcium because this can also be harmful.[4]https://www.petmd.com/exotic/conditions/endocrine/c_ex_gp_calcium_deficiency

Most grasses contain a lot of calcium and have a good calcium to phosphorus ratio. Grass adds a little calcium to your guinea pig’s diet. However, most guinea pigs will get enough calcium from their pellets and other vegetables and fruit you provide.

In the table below, you can find the ratio in different grass species.[5]See for these and other grasses: https://www.feedipedia.org

Grass speciesCa:P ratio
Timothy grass[1]:[1.42]
Bermuda grass[2.05]:[1]
Oat grass[2.35]:[1]
Buffalo grass[1.2]:[1]
Fiber percentage in grasses

Vitamin C

Guinea pigs are pet rodents that aren’t able to synthesize vitamin C themselves. They need to get this vitamin in their diets and they need plenty of it to stay healthy. Although multiple reputable resources cite different vitamin C needs, guinea pigs generally need between 10 and 50 mg of vitamin C per day (depending on your guinea pig’s condition).[6]https://vcahospitals.com/know-your-pet/guinea-pigs-feeding

Most guinea pig pellets contain enough vitamin C but you can supplement it by feeding fresh vegetables and fruit.[7]https://www.msdvetmanual.com/all-other-pets/guinea-pigs/providing-a-home-for-a-guinea-pig All grasses contain vitamin C but wheatgrass is very rich in vitamin C and other vitamins and minerals. Guinea pigs can eat wheatgrass (also known as cat grass) to add extra vitamin C to their diet.

Chewing material

A lack of chewing material can also cause the teeth not to wear out properly, which can cause malocclusions. When your guinea pigs have dental issues, they will have it more difficult to eat. It might even be impossible for them to eat properly.[8]Meredith, A., & Redrobe, S. (2002). BSAVA manual of exotic pets (No. Ed. 4). British Small Animal Veterinary Association.

Grass and grass hay is an excellent and cheap chewing material. Guinea pigs will need to chew thoroughly on the grass to be able to eat it. This will keep your guinea pigs busy for hours and help keep their teeth in perfect condition. 

Precautions When Feeding Grass

Pesticides and toxic chemicals (fertilizers)

A lot of gardens and backyards are treated with pesticides or fertilizers. These products contain many toxic chemicals and are hazardous for your guinea pigs. So if you let your guinea pigs graze in your backyard, ensure that you don’t use pesticides or fertilizers in the vicinity of the run. 

Urine and feces of other animals

Grass not grown indoors can contain urine or feces of animals such as dogs or cats. Urine and feces can be hazardous for your guinea pig. While it can be easy to check for feces, urine isn’t always easily detected in the grass. 

To reduce the risk that your guinea pigs eat grass that contains (traces) of urine or feces from animals, you should only feed grass from your backyard and never let them feed on grass from a sidewalk, park, or forest.

If you’ve got a dog or cat yourself and let them out in your backyard, you should ensure that you don’t let your guinea pigs graze in the area where they urinated or pooped. 

Insects and parasite eggs

Grass from outside (garden, park, or backyard) can contain insects and parasite eggs. You’ll have to deal with this hazard when letting your guinea pigs graze in your backyard. Unfortunately, it’s impossible to eliminate this risk 100%, but there are ways to reduce the chance that your guinea pigs get sick from eating grass with parasite eggs.

When you let your guinea pigs graze in your backyard or give grass that originates from it, you should regularly visit a vet to check for parasites. Your vet can also deworm your guinea pigs. Deworming will remove any nasty parasites that your guinea pig might ingest.

Wet or frozen grass

Guinea pigs should never eat wet or frozen grass. If guinea pigs eat wet or frozen grass, they will likely get health issues (especially when they consume large amounts). Therefore, always ensure that the guinea pig run is placed on dry grass or that the grass you give is dry.

Toxic weeds and plants

Guinea pigs don’t know the difference between safe and toxic plants. So when you let them in a run, you should ensure they aren’t in the vicinity of poisonous weeds or plants. This article contains a complete list of toxic weeds and plants.

Lawn clippings

Grass that is mown will begin to ferment within a few hours. When ingested, the grass will continue to ferment. As a result, most – if not all – animals will get sick. 

Guinea pigs have a sensitive digestive system, and grass that has started to ferment can cause digestive problems (disrupting the balance of bacteria in the intestines). For this reason, you should never give lawn or grass clippings.

Moldy grass

Moldy grass can be a severe health hazard for your guinea pigs. Mold is a fungus and it produces mycotoxins. These mycotoxins can cause respiratory or other health problems. Therefore, you should check that the grass you provide to your guinea pigs is mold-free.

Suitable Grasses for Guinea Pigs

According to the website Lawn Love the most common grasses in gardens in the United States are fescues, bluegrass, ryegrass, bermuda grass, St. Augustine, and zoysia.[9]https://lawnlove.com/types-of-grass The most common grasses in European gardens are fescues, ryegrass, and meadow grass.[10]https://gardens.theownerbuildernetwork.co/2021/05/13/what-lawn-grasses-do-people-grow-around-the-world/ All these grasses are safe and suitable for guinea pigs to eat.

Timothy grass, orchard grass, and wheatgrass are generally considered the best grass species for guinea pigs.[11]See for example https://kb.rspca.org.au/knowledge-base/what-should-i-feed-my-guinea-pigs/ and https://animals.mom.com/type-hay-should-give-guinea-pigs-10661.html Wheatgrass can be sold in stores and online and is also known as cat grass. Timothy grass and orchard grass are sold in their dried form as hay and are also one of the most common hays you can buy in stores.

Feeding Instructions

How much grass can guinea pigs eat?

Guinea pigs can eat as much grass as they like (ad libitum). So, you can give your guinea pigs as much grass as they can eat. However, when you first feed grass to your guinea pigs, you should only feed a small amount and increase the amount gradually. 

What kind of grass can guinea pigs eat?

Guinea pigs can both eat fresh grass and dried grass (hay). Different species of grass can be given to guinea pigs. The most popular grasses for guinea pigs are Timothy grass, Orchard grass, and Wheatgrass. Wheatgrass, for example, contains a high amount of vitamin C and many vitamins and minerals.

How many times can guinea pigs eat grass?

Guinea pigs can eat grass the entire day and each day of the week. So there is no limit to how many times you can give grass to guinea pigs. The same goes for hay, which is dried grass.

How to give grass to guinea pigs?

You can give grass to guinea pigs by giving hand-plucked grass blades, grass grown indoors, or by letting your guinea pigs graze in a run in your backyard or garden. 

If you’ve got a backyard, the cheapest and easiest option will be to buy a run and let your guinea pigs graze from the fresh grass. If you don’t have a backyard, you can still feed grass. You can buy Wheatgrass online or in pet stores or grow your grass indoors on a growth medium.

Related Questions

Can guinea pigs eat grass instead of hay?

Guinea pigs can eat grass instead of hay, although you might want to add hay to their diet for a bit of variation. If you cannot provide enough grass, hay will fulfill the needs of your guinea pigs.

Can guinea pigs eat too much grass?

A guinea pig can eat as much grass as it wants. However, it’s possible that your guinea pig is sensitive to grass and gets diarrhea from eating too much grass. If you notice this, you should limit the amount of grass you feed and replace it with hay.

Want to Learn More?

If you’re interested in learning more about guinea pigs as pets, please read the following articles:

If you’re interested in getting guinea pigs as pets you should also definitely read our beginner’s guide to keeping guinea pigs as pets and our guinea pig care guide.

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