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Best Hay for Guinea Pigs: Timothy and How Much to Feed
Timothy hay is the hay both the PDSA and VCA Animal Hospitals name for guinea pigs, and guinea pigs need a lot of it. The RSPCA says good-quality hay should make up the majority of a guinea pig’s diet and should be available at all times. This guide covers which hay the vet sources name, how much a guinea pig should have, how fresh grass fits in, and what to do when a guinea pig stops eating.
Which Hay Is Best for Guinea Pigs
VCA Animal Hospitals tells guinea pig parents to “offer unlimited timothy or other low-calcium hay throughout the day.” The PDSA, a UK veterinary charity, says “Timothy hay is a great option.” Timothy is the one hay type both sources name. The Merck Veterinary Manual says to “Offer good-quality grass hay (such as timothy or orchard grass) as the main food in your guinea pig’s diet.”
Timothy hay is widely regarded as the best hay for guinea pigs because it supports their overall health in multiple critical ways.
VCA’s phrase “other low-calcium hay” matters when a guinea pig parent wants a change from timothy. A different hay should be a low-calcium one, and a vet can say which hay fits a particular guinea pig. In its answer about calcium in vegetables, the PDSA adds that guinea pigs with a medical condition affected by calcium, “such as a urinary or bladder problem,” should get a vet’s advice.
Why Guinea Pigs Need Hay Every Day
Hay does two jobs, and the PDSA names both. First, “Their teeth grow constantly so need to be continuously worn down by chewing on fibrous foods.” Second, hay “keeps their guts moving, as lacking fibre can lead to a life-threatening condition called ‘gut stasis,’ where the digestive system slows down or stops working.”
The RSPCA gives the same two reasons: “guinea pigs need hay and/or grass for their digestive systems to function properly,” and “eating hay helps wear them down to keep them at the correct length and shape.” It adds that “The wrong diet can cause serious dental disease.”
VCA puts hay first among all foods: “Hay is the most important part of a guinea pig’s diet.” It says hay “provides the fiber guinea pigs need to keep the bacteria in their intestinal tract healthy and functional.”
How Much Hay a Guinea Pig Needs
The PDSA says guinea pigs should always have plenty of fresh feeding hay and grass, and that “It should make up 85-90% of their diet; unlike pellets, you can’t overfeed it.” VCA says to offer hay “throughout the day.” The RSPCA says it should be “available at all times.”
Guinea pigs are grazers. The PDSA says “you should expect to see them eating hay and/or grass day and night.”
The PDSA also gives a way to set hay out: “The best way to encourage natural foraging behaviour is to scatter large piles of hay and grass throughout your guinea pigs’ living space.”
Fresh Grass Next to Hay
The RSPCA says “Fresh grass should also be provided as often as possible, ideally every day.” For guinea pigs kept indoors, it suggests “pots of fresh, growing grass” to encourage natural grazing behaviour. The PDSA says fresh grass can be eaten straight from the lawn, or picked and brought in for guinea pigs that cannot go outside.
Both sources warn against one kind of grass. The RSPCA says “Never feed your guinea pigs lawnmower clippings, which will upset their digestive systems and make them ill.” The PDSA says mown grass clippings ferment quickly and “can make guinea pigs very unwell.”
Hay, Pellets, and Vitamin C
VCA says “Vitamin C should be provided through their pelleted food and vegetables,” because guinea pigs cannot make their own and can develop scurvy without enough. It gives a daily range: “Guinea pigs need 10 mg to 50 mg of vitamin C per day,” and the amount “depends on factors such as age, overall health, stress, and pregnancy.”
The RSPCA says a fresh portion of grass-based pellets should be available daily, and that these provide essential vitamin C. The PDSA says pellets should be “grass-based and specifically made for guinea pigs.” VCA says pellet vitamin C breaks down quickly, so pellets should be used or replaced within 90 days of the date of manufacture. Fresh vegetables are the other source of vitamin C, and they are part of providing the right diet.
The RSPCA explains why pellets are given fresh each day: “Vitamin C is destroyed over time and more quickly with exposure to the air so a fresh portion of pellets must be given each day.” It says not to top up the bowl. The PDSA says to scatter pellets throughout the cage instead of putting them in a bowl, to store them “in a dry, cool and dark place,” and to avoid a muesli-style mix: “never feed a muesli-style mix.”
Where Hay Fits in a Day’s Food
The PDSA lists a day’s food for each guinea pig in this order: hay and grass in unlimited amounts, then “one tablespoon of pellets per adult guinea pig each day,” then “one cup of fresh vegetables, greens and foraged foods daily.” It tells pet parents to give “a variety of at least five to six different types each day.” Fresh drinking water is on the same list, with constant access.
VCA lists the same three foods in the same order: unlimited timothy or other low-calcium hay, a smaller amount of commercial, high-fiber, timothy-based pellets, and a variety of fresh leafy greens and vegetables. It says to supplement hay and pellets with the vegetables.
Young, Pregnant, and Nursing Guinea Pigs
The RSPCA says guinea pigs “may need a larger portion of pellets if they’re growing, pregnant, nursing or underweight,” and to “Ask your vet for advice on portion sizes if you’re not sure.” The RSPCA also says hay should be available at all times. VCA says a guinea pig’s vitamin C needs depend on age and pregnancy, and that a vet can say how much a particular guinea pig needs.
Alfalfa and Timothy
The Merck Veterinary Manual mentions alfalfa in its section on pellets: “Alfalfa-based pellets are higher in calcium and are suitable for young, growing, or pregnant guinea pigs. For adult guinea pigs, timothy-based pellets with less calcium are preferable.” It adds “Ask your veterinarian for pellet recommendations.” For hay, it names timothy and orchard grass.
VCA’s hay advice for every guinea pig is “unlimited timothy or other low-calcium hay,” and the RSPCA says hay should be available at all times.
What a Hay Supplier Says About Fresh Hay
Speaking to the experts at HayDay, who comment, "Fresh, green, and fragrant hay encourages activity, while dust-free varieties help prevent respiratory irritation.
A steady supply of clean hay also provides mental stimulation, preventing boredom and unhealthy chewing habits."
When a Guinea Pig Stops Eating Hay
The PDSA warns that “If a guinea pig stops eating, they are at risk of developing a life-threatening health problem, called gut stasis.” It says weight loss can be a sign of illness, and that weighing guinea pigs regularly is the best way to check they are eating properly. Its advice is direct: “It’s essential to contact your vet if you’re worried that your guinea pigs are eating less, or if you notice a significant change in their weight.”
VCA says guinea pigs do not adapt easily to changes in food, and that “Sudden changes can result in a refusal to eat.” It says to make any change to a guinea pig’s diet gradually. The PDSA says to change a diet slowly over two to four weeks, mixing a small amount of the new food into the current food and increasing it a little each day.
Setting Up Hay in the Home
Hay goes in the living space, which is part of setting up the right habitat. Bedding covers the floor of the same space, and a bedding guide for guinea pigs helps with that choice. VCA also says fresh, clean water should be available 24 hours a day, and that a vet should examine a guinea pig once a year, one more part of proper care practices.
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