Guinea Pig Hay 101: Why Do We Feed Our Mates Dead Grass?

Hay has become so much a part of our common language and culture, that it can be easy to forget to step back and consider where it came from in the first place – and why we use it to feed our pets.

This is particularly relevant to guinea pigs… we feed them approximately 25kg of the stuff (each) every year.

I guess that’s not surprising when you consider that hay is the single most recommended guinea pig food.

Well… that is if you listen to the vets, pet stores and other ‘experts’ (all of whom are in the pockets of the guinea pig pellet manufacturers).

What’s that? Your ears perked up?

They should. Read on for a short history and science lesson that will explain why the truth about guinea pig hay isn’t as straight forward as you thought.

What is Hay Anyway?

First of all, let’s start at the very beginning.

Hay is simply grass (quite possibly the same grass that grows in your Aussie backyard – perennial ryegrass – except you keep yours trimmed before the seed head grows). But more specifically: hay is dead, dried grass.

With me so far?

In which case, you’re probably now wondering how the nutrient content of something that is dead and dried (hay) stacks up against something that is alive and fresh (grass).

Luckily there is a fair amount of scientific research available on this subject.

Technically, hay is considered as preserved pasture plants that have been dried to less than 20% moisture content. As a general rule, fresh plants in the pasture are around 80-86% moisture.

As water dries out from the dead grass, it’s weight drops. Thus, hay is considered to have a higher ‘dry matter’ value than fresh grass. Of course, this means that a guinea pig has to eat around 4x as much (in weight terms) fresh grass than hay, to achieve the same level of calories. This may give the false impression that hay is somehow more nutritionally dense than grass.

However, what happens when we adjust for ‘dry matter’ values?

Not only does grass contain higher levels of calories and protein than hay, but grass provides much higher levels of vitamins too. Live grass contains the full range of vitamins except vitamin D (for which sun exposure is necessary).

When cut, dried and baled for hay, the vitamin C and E and B vitamins in grass quickly drop.  Vitamin A is also lost, but more slowly and some remains in most hays with a good green color.

Vitamin C is well known as a vitally important vitamin for guinea pigs. Let’s take a look at what this 1933 study found in alfalfa hay:

Green alfalfa has an abundance of vitamin C as evidenced by the continued good health of the guinea pigs in this study, but vitamin C is lost when the alfalfa is cut and cured. The guinea pigs would eat the cured alfalfa until scurvy had developed, to such an extent that they were unable to eat the hay. There is practically no vitamin C in alfalfa hay, which confirms other investigations in this field.

Alarm bells ringing yet? They should be.

Why Do We Feed Guinea Pigs Hay?

This is where we need to start our history lesson folks.

The reason that we have so much research on the nutritional value of hay, is because of one thing: a little something called agriculture. Or more specifically, the $5 Trillion dollar global agriculture industry.

Agriculture basically refers to the domestication of plants and animals for human purposes… and it hasn’t been going on all that long. Cattle were first domesticated from the wild aurochs in the areas of modern Turkey and India around 8,500 BC – the blink of an eye in evolutionary terms.

Our ancestors figured out that if they could keep animals year round, they would have a constant supply of fresh meat and dairy. Great. But this presented a new dilemma… how to keep these animals alive during the winter.

In nature, just as other undomesticated ruminants do to this day, cows migrate with the weather. In other words – when winter comes and the grass dies – they bugger off to fresher pastures where they can find fresh greens.

The solution of course, was to store and preserve feed for the animals – harvested during the summer – to provide a source of nourishment for them during winter. Hence the invention of hay!

As you can tell then, hay is certainly not new. If you’re interested, Columella (d. 70 AD) mentions hay 54 times in his epic work concerning Roman agriculture, De Re Rustica. Sadly, he doesn’t mention guinea pigs.

But the hay and forage used in these most ancient of times would have been a far throw from the sort we’re used to today.

The felling of grasses used to be a manual process (sickle and sythe anyone?) and was stored manually, fork load by fork load, in barns. Hay was a precious community, used sparingly to keep every last animal alive, after every last hint of fresher fodder was consumed. It was not until the Agricultural revolution of the 1750s and the following advent of hay baling machines, enabling truly intensive farming, that ‘bales of hay’ as we know them today began to appear in such overwhelming surplus.

Allow all this to sink in for a moment.

Nobody in the livestock industry is saying now that it is (or ever has been) ideal to feed cattle, horses or any other animal (such as guinea pigs) a diet based mainly on hay.

Hay has historically been fed to animals simply – and only – when enough fresh pasture is not available.

It is widely recognized in the equine and dairy industry that fresh grass is nutritionally superior to hay and produces healthier animals. Even the horse supplement makers say that their products are only needed when unlimited fresh grass is not available. However, agriculture is huge business – and at the end of the day the cost of fresh pasture can be prohibitive (compared to cheap hay plus a bunch of vitamin powders).

Read that again guys… in animal health terms, the accepted preference is for horses and cattle to eat fresh grass.

So why on Earth do we so often hear the line that guinea pigs must eat a diet mostly based on hay?

Further investigation and digging is needed to find out exactly what is going on here…

A Short History Of The Guinea Pig Hay Industry

Our story takes us to the very first civilization to domesticate wild guinea pigs.

Guinea pigs are thought to have been domesticated in traditional Andean households for around 5000-7000 years. They were (and still are) kept indoors, but not always in cages – a high stone sill at the entrance of a room is used to keep cavies from escaping. Some households build special rooms or cubby holes for their animals, or more typically keep them in the kitchens.

Guinea pigs were (and still are in South America) fed barley, kitchen scraps of vegetables, and the residue from making chicha (corn beer).

So for most of their history, domestic guinea pigs were fed barley, corn and vege scraps. Not exactly great for them… but not exactly hay based either.

Moving forward a few thousand years, guinea pigs became popular pets in medieval Europe. I wonder what they were fed?

As luck would have it, we have a recent research study to tell us just that.

What’s more, analysis of the chemical elements in the guinea pig’s bones revealed the animal had eaten mostly human refuse – without any trace of corn, the typical diet of domestic guinea pigs in South America.

Still no mention of the H word. The plot thickens. However, what of the United States in the 1800s? Surely they were feeding their guinea pigs hay by that time…

The 1851 book Domestic pets: their habits and management, has the following to say:

Guinea pigs should be fed in the same way as rabbits – and are exceedingly fond of tea leaves – which however should not be given too abundantly. Probably the best food for them is parsley or carrots.

OK, then. So what of rabbits?

Rabbits may be fed with almost any kind of vegetable matter, but the best food for them consists of celery parsley and carrots. They are very fond of cabbage stumps and lettuce but they should be given sparingly. They will also eat turnips parsnips and even potatoes in a raw state. They ill also eat dandelions sow thistles and other kinds of weeds.

Hmmm, no mention of the dry stuff whatsoever.

So, it would seem that for the bulk of their several thousands years of domestication, guinea pigs have gotten by on human scraps, primarily corn (in South America) and greens (in North America and Europe). This is a grisly story in itself. Guinea pigs are truly adaptable creatures, able to survive (although certainly not thrive) on a wide variety of domesticated diets, just as they survive in a wide variety of habitats in the wild, from dry grasslands to marshes.

That said, at least that kind of relatively fresh food would have contained some vitamins.

Anyway, the big question is still nagging me. When exactly did hay first start getting mentioned as the de facto food for guinea pigs?

To answer this question let’s take a quick look into the first unscrupulous guinea pig breeders of the 1920s and the first seeds of mass commercialization in the pet industry.

Finally, in 1922, we get a mention of hay.

It really isn’t very promising though I’m afraid. The book “Profit In Cavies” by J. A. Roberts is a rather depressing read. It tells the story of an entrepreneur in an era when widespread interest in guinea pigs as pets, show animals and the development of different guinea pig breeds was rapidly accelerating.

He presents a rather morbid business model of how the average man on the street can become rich off the back of cavies. Funnily enough, it’s based on minimizing costs and maximizing outputs.

Although… to J.A’s credit, even he acknowledges that hay can be substituted for fresh grass:

The feeding of guinea pigs is a very simple matter. Their main food is good, dry hay or grass, and their green food consists of any kind of food that is not harmful, such as alfalfa, barley, carrots, lettuce and cauliflower, etc.

Phew, we got there.

But what does this all mean?

When adding all of this up, I come to two conclusions:

1) Hay has become the defacto diet of guinea pigs primarily out of sheer historical happenstance (it just happened to be widely available and cheap in the time when guinea pigs were first commercialized)

2) The narrative that guinea pigs need hay (which is particularly low in vitamins) as the bulk of their diet supports the guinea pig pellet manufacturer’s argument for the need of a fortified food product (pellets).

After all… since there’s no Vitamin C in hay, they’ll need to get it from pellets, right?

It would be much less profitable to suggest that a guinea pig’s natural food is grass (rich in Vitamin C) and that they can get all the Vitamin C they need simply from grazing on your lawn.

Where Does Modern Guinea Pig Hay Come From?

To fully understand modern guinea pig hay products, we need to understand the hay making process and how nutrients are lost along the way.

First, bear in mind that the shelf life of hay is generally said to be 3 years. While hay can theoretically be kept indefinitely (under perfect storage circumstances), it won’t be worth much to your guinea pig by then.

See, the calorific and protein value of hay is relatively stable over time. This is great news for livestock farmers, who are primarily concerned with keeping their cows alive through winter – but less good news for you as guinea parent… who just wants to give the most fulfilling and nourishing meal to your pet.

A 2012 study using the latest HPLC analysis techniques found fresh fescue pasture contained approximately 10 times more vitamin A equivalents than cured hay. What’s more, there was a further 11% loss per month whilst in storage.

In other words, after about 10 months there’s barely any Vitamin A content left in hay for your guinea pig to enjoy.

With this in mind, next time you go into the pet store and pick up a bag of hay for your guinea pig, check out the “Freshest By” date (if you can find one).

Food for thought, isn’t it?

What this doesn’t give you a picture of though, is how long the hay you buy for your guinea pig has been hanging around various anonymous warehouses in different parts of the world, before you even see it. Let’s take a look at a typical guinea pig hay supply chain.

As you can, if you were imagining your pet shop was selling farm fresh hay straight from the field, it might be time to take a second look. There’s no telling how long the hay you buy has been hanging around in any one of these stages.

In reality, allowing for warehousing, receipt and transport between these 4 different storage locations (which may well be at different ends of the country), it wouldn’t surprise me if it’s at minimum 4-6 months from the time the hay is cut to the time you buy it – during which time the vitamin content is slowly leaching out day-by-day.

That’s if you buy commercial guinea pig hay from the big pet chains of course.

How To Tell Good Hay From Bad

Look, it’s not all doom and gloom.

While the odds of getting decent, fresh hay in Australia seem to be stacked against you – it is totally possible. You just need to know where and what to look for.

The graph on Vitamin A loss above isn’t just theory either, the color of your hay is a good indicator of current beta-carotene levels. Greener hay will have higher levels than hay that has yellowed. It all makes sense.

• Bright Green: higher vitamin and protein content
• Dark Brown: indicates heat damage
• Lighter Yellow: sun bleached, lower vitamin content
• White to Gray: indicates mold; do not feed to guinea pigs

You want strongly green colored hay with a strong, fresh sweet smell. It should smell delicious, as if it has come straight from the field. If it doesn’t… then it hasn’t.

Types Of Hay For Guinea Pigs (in Australia)

So, despite the fact that for much of their domestic history guinea pigs have not eaten hay, hay is not inherently bad for them. It is still grass after all – their natural diet. While a fresh grass based diet would be preferable to a hay based one for most guinea pigs, this is not a viable option for many city dwelling Aussies.

The main issue you face as a guinea parent is making sure your guinea pig’s hay is truly fresh, so that at least it has some vitamin content.

So let’s take a look at the main types of hay that are available for your guinea pig in Australia:

• Timothy Hay
• Orchard Hay
• Meadow Hay
• Pasture Hay (a.k.a. Ryegrass Hay)
• Oaten Hay

All these hays are ‘grass hays’. There is another type of hays called ‘legume hays’, that funnily enough are from dried legumes. Since guinea pigs are graminivores (grass eaters), legume hays are not suitable for them.

Which type of hay should you pick for your guinea pig… that’s a great question. There are various nutritional tables available for different types of hay that list protein, fibre, calcium, phosphorus and vitamin levels. But the fact is that multiple research studies have shown all these factors vary wildly between different batches of hay, depending on growing conditions, soil quality, storage, age, sunlight exposure and many other – probably unknown – variables.

Think about it, it is much more likely that the soil quality has a more profound effect on the end nutrient value of a grass grown, than the seed species itself.

The only way to truly know the nutrient profile of a particular bag of hay is to send it away for lab analysis (at a cost of about $160).

Therefore, we recommend simply picking the freshest, greenest and best smelling hay available for your guinea pig – regardless of the specific type (as long as it’s from the above list of 5 suitable types).

For example, we are currently feeding our piggies Oaten hay direct from the farm. Which, if you listen to the charts and tables isn’t the most ideal type – however it’s far fresher, far greener and smells far better than even the most expensive Timothy hay that we could lay our hands on.

Problems With Modern Hay – Mould, Dust,

I’ll never forget the experience of coming home from one of the biggest pet shop chains with my new bag of hay under arm, pumped and excited to rip it open for my piggies. I thought I’d gotten a good deal. Little did I realise, that upon closer inspection, the whole bag was littered with pieces of pale, mouldy hay!

Believe it or not when I returned this hay to the pet store, the assistant’s first response was “Oh – that’s normal in hay”. Errrr, excuse me?

The sad thing is, when it comes to the small pet industry, she’s probably right.

The other common problem in these commercial hays is ‘dust’. You’ll know it when you see it. It’s essentially the tiny ‘scraps’ and ‘off cuttings’ that are a byproduct of the manufacturing process  -but haven’t been sufficiently caught by the brand’s quality assurance process.

Hay dust is terrible for your guinea pig’s health! It can cause them all manner of respiratory system issues.

Where To Get Good Fresh Hay in Australia

We’ve been experimenting with a few different options since the above mentioned ‘mould’ and ‘dust’ experiences.

We’ve given up on the big pet stores and guinea pig hay brands (you know who they are). Even their most premium products are more expensive and lesser quality than local stuff you can get virtually direct from the farm, via eBay or Gumtree. Look what we got on eBay recently:

We’d suggest taking a look on Ebay, Craigslist, Gumtree, etc and seeing what you can find. If you have farms locally, pop in and have a chat with them! You’ll be doing your piggies a favor.

It’s worth mentioning there is a cool company called GuineaDad in the US (no affiliate, just looks like a good product) providing good quality, dust extracted hay – without the supply chain issues. Sadly they don’t ship to Australia.

So Do Guinea Pigs Really Need Hay To Survive?

This is an emotional topic, as guinea parents we just want to do the best for our little guinea babies! Any suggestion that what we’ve come to accept as fact could be fallacy is difficult to swallow.

But we’ve all be fed the same narrative by the $87 Billion dollar pet food industry… and it all has an hidden underlying commercial agenda. We believed it all too, until we started to question things and look deeper.

There are many myths surrounding guinea pigs… and many of them are not in our (or their) best interests. While many guinea parents do feed their pets a healthy, rich diet based on fresh hay, herbs and veges – widespread education regarding the benefits of a grass based-diet has not been sufficient to date – and has been intentionally hampered for commercial reasons.

If your interest is piqued at this point, make sure to check out our full page on guinea pig grass.

To finish off, let’s take a look at a few of these common myths.

The reason guinea pigs need hay is because of the fibre

Umm, a blade of fresh grass that has been dried into hay has literally the exact same fibre content. It’s the same blade of grass! Since piggies would need to consume around 4x the volume of grass to get the same calories as a hay based diet (hay is more calorifically dense, but almost devoid of vitamins), they will actually get 4x more fibre from a mainly grass based diet.

The reason guinea pigs need hay is to wear down their teeth

It’s the silica in grass that wears down the guinea pig’s teeth – and again there is the exact same amount of silica in a blade of grass whether it’s fresh or dried into hay.

Even though grass is softer than hay, a 2018 study looked at this exact question and found tooth volume was the same in guinea pigs fed a diet of grass grass vs fresh hay over 3 weeks.

The reason guinea pigs need hay is because of their digestive system

Guinea pigs are gramnivores (grass eaters, like horses, cattle, capybara, etc), their digestive system is specially made to eat grass. That’s why we offer them hay, as a substitute for grass. Wild guinea pigs live in varied habitats including marshes – where dry grass is virtually non-existent.

Final Thoughts

Hay is just a product of humans – and wild guinea pigs were doing just fine before we came along.

If your guinea pig is used to a hay and pellet based diet, you would need to think carefully and slowly about how to potentially transition them to a grass-based diet, over an extended period of time – monitoring their health along the way.

We have been transitioning our 2 piggies to a grass based diet over the last 2 months and they now eat approximately 60% fresh grass, 30% fresh hay and 10% veges/herbs.

We are slowly increasing the amount of fresh grass we offer them each week – and noticing that as we increase this, they naturally eat less hay. Their eyes are brighter, their coats are shinier, they have abundant energy and most importantly of all – their poos are extremely healthy!

I’ll be updating this post in a few months, when we fully complete the transition (with hay still available ad libitum, as it is now – they just prefer to eat real grass when it’s there)