UNLIMITED Timothy Hay (or a grass hay) is required for guinea pigs. Hay is not just a treat! For young cavies under the age of 4 months and pregnant or lactating mothers, alfalfa hay is also recommended. For those cavies, you could mix half Timothy and alfalfa. Since alfalfa hay is a legume, not a grass hay, it's too high in calcium and should only be given to adult cavies as an occasional treat. Timothy and alfalfa are types of hays, not brands of hay. Other acceptable grass hays include orchard hay or meadow hay.

Hay should comprise 70-80% of their diet!

Lack of abundant hay can result in:

• DENTAL PROBLEMS
  This is no minor health warning. This is one of the most common, most expensive to treat, most painful conditions that a guinea pig can suffer. A rodent's teeth continue to grow (and fairly rapidly) over their lifetime. They need rough chewing action (hay with silica) to keep their teeth ground down. Misaligned teeth, and is almost always a result of diet. This can easily lead to premature death after extreme mouth pain and starvation.1
• Bloat (life-threatening) The long fibers of hay stimulate muscle contraction of the intestines to improve and maintain gut motility (to prevent gastrointestinal obstruction).
• Diarrhea (life-threatening)
• Anorexia (life-threatening)
• Obesity - can contribute to stones, UTI's, diabetes and a long list of other ailments.
• Alopecia (hair loss)
  In larger cages, it’s a good idea to have hay available in more than one location. It can help prevent alopecia in guinea pigs, especially pregnant guinea pigs.2
• Barbering - chewing the hair of other cage-mates
• Biting - cage walls or cage bars
• Boredom - general dissatisfaction that can contribute to the other issues.

Guinea pig droppings should be large and healthy looking. If they are not, look to the ratio of hay in their diet relative to their pellets and fresh food.

• Treats and chew sticks are not efficient at wearing the teeth. Most guinea pigs ignore chew sticks anyway. Save your money. It's all about the hay.
• Hay cubes and other compressed hay products are not acceptable alternatives to providing hay in the diet.

In the wild, guinea pigs will tunnel, burrow and hide in long grass. They'll eat the grass stems and shoots, providing much wear for their teeth and fiber for their gut. We need to provide a similar environment for our domesticated guinea pigs as well. If they potty or poo on their hay, that's okay. That doesn't mean the hay is wasted. They love it. Keep it fresh and refreshed daily. But, do not allow the hay to become bedding. It is not appropriate as bedding. It's okay if they soil it as long as you refresh it frequently.

Nothing says guinea pig popcorning like a boatload of clean, green, grassy-smelling fresh hay! They will delight, squeak and popcorn with new, fresh hay.

Sometimes there is concern about the possibility of getting mites or other bugs or parasites from hay. Hay does not harbor mites. Mites need a living host to survive.

But it messes up our pretty fleece!​

Deal with it! Guinea pig life is not about neat, pristine-looking cages. It's about providing them a stimulating, healthy environment. Hay in one small hay rack is NOT acceptable. Hay that is hard to get at is also not acceptable. If you have a Cavy Cafe or large litter area in your cage, consider putting big handfuls of hay on top of the bedding on the floor of it instead of or in addition to a traditional hay rack. However, do not close off a large section of the cage just so it can contain hay. They still need room to run around and do their zoomies and such.

Hay Play​

Paper bags are great for putting hay into. They recreate the tunnel that guinea pigs would naturally seek out in the wild. Presenting hay like this is more natural than when in hayracks etc.

Hay Quality Matters​

Depending on the season and the weather at the farm, sometimes the hay may be drier or less fresh than at other times. Don't give up on trying hay from a source if you get one shipment that may not seem up to snuff. Ask them about their season. Mother nature cannot be guaranteed to deliver!
If you notice any clumps of hay that seem "welded" together, that hay has likely been exposed to moisture and may be moldy. Any moldy or questionable hay should be discarded.

Damp hay can expose animals to potential respiratory problems and if the hay has become dusty (as damp hay does). Guinea pigs love to forage and it is false economy to use hay that is not up to standard. Damp hay also brings with it the risk of introducing fungal spores to the environment; these can affect a guinea pig's health.

There are a variety of hays available for guinea pig owners but the best and only hay that should be fed to guinea pigs is ‘good grass hay’. Good hay is clean, dry, smells of grass or similar and not musty or dusty, looks golden or green in color depending on origin. It is interesting to note that in the UK farmers need to heavily fertilize their fields before getting a second crop of Timothy Grass because it is significantly slower growing than the more common Rye. Although guinea pigs seem to prefer the leafier second cut it is worth bearing in mind that it is likely to be more heavily fertilized unless conditions have been particularly favorable which isn't typical.

Alfalfa Hay​

Alfalfa hay is rich in protein and calcium, but when combined with pellets it doesn’t have the proper ratio of calcium and phosphorus. This can lead to improper gastrointestinal motility, such as diarrhea. It also may predispose certain guinea pigs to calcium oxalate bladder or kidney stones. Timothy hay is a better choice. It’s important to keep your guinea pig sleek, so cut down on the amount of protein and calorie-rich pellets while feeding timothy hay.

Timothy hay -- 1st, 2nd or 3rd cut?​

As the name implies, the 1st cutting is the first crop taken off a field in any given year. The 2nd cutting is the second crop from that same field in that given year. Sometimes, some farmers will get a 3rd cutting out of a field if Mother Nature cooperates with good growing conditions. Unless your hay specifically states that it is 2nd cut, assume it is 1st cut -- which is the case with the majority of big retail hay brands available in the pet stores.

• 1st cutting: the 1st crop taken from a field in the year. Typically happens anywhere from the beginning of spring to mid-summer. The first cut may have left-over stalks and weeds from the wintertime. The 1st cut still has seed heads on the hay. The first cut is more mature, containing a higher stem-to-leaf ratio and is coarser in texture. It is actually healthier as it is higher in fiber and lower in protein than a second cutting timothy. But many small animals do not find it as appetizing. It's not as soft as the 2nd cut.
• 2nd cutting: the 2nd crop taken from a field in the year. It is an immature cutting of hay and therefore contains a higher leaf-to-stem ratio. It is harvested in the late fall (middle to end of season) and is very soft and palatable to small animals. The 2nd cut is taken after a good amount of growth from fertilization, watering and sunlight, yielding more protein and less fiber content. 2nd cut is softer than 1st cut.
• 3rd cutting: the 3rd crop taken from a field in the year. This cut is from the end of the season, after the grass has gone to seed, so it's pretty dry and not as nutritious, but depending on the seasonal factors (weather, temperature, and moisture) it can also be very soft and leafy. Not all farmers in all seasons produce a 3rd cut.

Where to get good hay​

Packaged Timothy hay found in stores is typically dry and stale and less nutritious compared to what you can order from a farm -- either locally or online.

If you must buy hay at a pet store, look for the greenest, freshest hay possible. Ordering direct will save you 50-75% or more, especially if you order larger quantities.

Buy Local​

Buy Online​

Buy in Bulk​

Buy the Bale! If you have a lot of guinea pigs and can store some extra hay, then finding a local source of good Timothy or grass hay by the bale is definitely the cheapest way to go. A bale of hay from a farm or hay distributor is around $25 to $40 and that's for approximately 200 pounds of hay! Some feed stores will let you buy partial bales (flakes) or in bulk. Feed store prices may be slightly higher. Some farm or hay sources will let you buy half bales.

Will it keep?​

Hay can be stored for many months, depending on how fresh it is and if kept in the proper conditions (see some of the links below). It should be opened to breathe when you get it. Keep it in a dry and well-ventilated place, not in plastic. A wooden or cardboard box is ideal. If you get a bale or a partial bale, it will stay fresher longer if you break up the bale as little as possible. If you get a whole bale, try standing it on end, pop the strings, and use a section (or flake) at a time off the top. Just be careful as some bales expand more than others. If you get a shipment that comes in a plastic bag, open the bag, leave the hay in the box, and cut and remove the plastic bag entirely.