What’s the deal with Hay?

What’s the deal with Hay?

Hay is a critically important part of the diet of pet rabbits, guinea pigs, chinchillas, prairie dogs, and other small herbivorous mammals.  The question is, why is it so important?  Why can’t hay be replaced by pellets and veggies?

History of Hay (Grasses)

Let’s go back to the very beginning, to set the stage for the importance of hay through the ages.  Grasses first evolved in the Early Cretaceous Period, 145-110.5 million years ago.  The earliest evidence we have of grasses in the fossil record are from microfossils of grass found in the teeth of a Hadrosaur dinosaur (commonly called “Duck Billed Dinosaur”) dating from 113-100 million years ago.  The first grasses appeared in a very different world than today – a warmer, wetter, jungle world, dominated by ferns and cycads (palm like trees).  Grasses lived in the shadows of these vast forests, waiting for their turn to take over.

Grasslands, like we know today, did not appear until much later in time, about 26 million years ago.  The global climate was cooling and drying, causing the forests to fragment and pull back to warmer and wetter zones closer to the equator.  This shift in climate and forest cover left vast spaces for the hardier grasses to take over and multiply, allowing them to create the first grasslands.

When grasslands developed, suddenly there was this huge opportunity for animal species to move into new biological niches.  Grasses were this amazing potential food source that grew in vast amounts, and grew even more the more you ate it.  Wow!  Amazing!  Sign me up!  However, grasses came with a significant catch – they contain silicates, which are essentially tiny bits of sand, which would wear down the teeth of any animal that tried to eat it.  Within a few years, their teeth would wear down to nubs, and they would then starve to death.  Big problem!  To overcome this, several different groups of mammals – rabbits, rodents, horses, ruminants (cows, sheep, goats, deer, antelopes, etc), and so on – all independently evolved teeth that could handle this challenge.  Rabbits and rodents developed teeth that were “Hypsodont” (long crowned and long bodied), “Elodont” (continuously growing), and “Lophodont” (had folds of enamel to make them stronger and keep them sharper).  These specialised teeth made them more able to handle this rough food item.  This adaptation allowed these species to flourish in a completely new ecosystem for millions of years, up until the present day.  Isn’t that neat?  But wait!  There’s more!

The importance of hay to prevent dental disease

Knowing the evolutionary history of grasses, rabbits, and rodents gives you the first clue as to why hay is so incredibly critical to our pet rabbits and rodents.  Rabbits and rodents evolved these amazing teeth that were incredibly strong and were designed to chew this very rough food source.  Rabbit upper incisors (the front teeth) grow at a rate of 2 mm per week and the lower incisors grow at a rate of 2.4 mm per week.  That means if they are not wearing down their teeth at all, within a month they would be about 1 cm longer.  Yikes!  When we do not feed them grasses orhay, their teeth are not worn down the way they are supposed to be, which leads to overgrowth of the teeth.  As such, while dental disease is a multifactorial process, one of the most common causes of dental disease in pet rabbits and rodents is insufficient hay intake.

Another common cause of dental disease is also related to insufficient hay intake: not enough time spent chewing per day.  In the wild, rabbits spend up to 70% of their time grazing.  When they are eating, they are exercising all the chewing muscles, and wearing down their teeth.  In captivity, especially when rabbits are fed primarily/exclusively pellets, they consume all of their daily calories in a very short period of time (minutes), and then are not chewing for most of the day.  This is both very boring for the rabbit, and leads to overgrowth of their teeth.

Finally, a subtler, and more insidious way that a low-hay and primarily pellet diet can lead to dental disease is in how pressure is applied to the teeth when chewing different food items.  When rabbits chew on hay, the pressure applied to the teeth is primarily side to side, across the top of the tooth.  This is what rabbit teeth evolved to do, so they are well designed to handle this pressure.  When rabbits eat pellets, (or even worse, “gourmet” diets that contain very hard things like seeds or dried peas), there is a crushing pressure that causing pressure to go down the body of the tooth to the apex (“root”) of the tooth.  If rabbits are eating mostly pellets, this pressure can become too much for the apex, and it gets pushed backwards through the jaw.  This can lead to deformity of the tooth as it is being formed, and lead to increased curvature orbending of the teeth in the jaw.  When these oddly bent teeth reach the mouth, they don’t meet their partners in the opposite jaw normally, and they don’t get worn down through the normal process of chewing.  This causes dental spikes that eventually run into the cheek or the tongue, causing ulceration, infection, and pain.  Once this shift of the apex of the tooth has happened, there is nothing we veterinarians can do to get it to move back into a normal position.  Given that rabbits have continuously growing teeth, this means that that rabbit will have dental problems for the rest of its life.

The importance of hay in digestion

Hay and grasses are also critically important in the function of the gut.  Rabbits and rodents have a beautifully developed system for digesting a diet that is rich in fibre.  They have a stomach and small intestine that is actually very similar to “monogastric” (single stomached) animals like us.  Then the small intestines reach a special part of the gut, called the cecum, and that is where the magic happens.  The gut contents are separated into short fermentable fibres, and long indigestible fibres in the upper part of the colon.  The long indigestible fibres are sent down the colon and made into the fecal pellets that small mammal owners are all too familiar with.  The short fermentable fibres enter the cecum, which contains a very special and interesting host of different bacteria, as well as some types of fungus, and some types of protozoa (single celled organisms).  This microflora ferments the fibres, producing and unlocking lots of nutrients, including volatile fatty acids (which are used as an energy source), vitamins, and electrolytes.  The cecum then contracts, pushing the contents into the colon, where it is packaged in mucus and rapidly passed to the anus, and the animal re-ingests this special material, called a “cecotroph”.

The microflora within the cecum shifts and changes according to what the animal is eating, age, health status, etc.  A recent study showed that rabbits that are fed a primarily hay-based diet have a much more diverse microflora in their gut than those that are fed exclusively pellets.  Just like in wild ecosystems on Earth, diversity is important, because it helps maintain balance and is more resilient to change and stress.  If a rabbit or rodent has a healthy microflora in their gut, they are able to handle minor changes that happen, such as when a new food item is introduced.

When rabbits and rodents are fed diets that are high in sugars and starches (fruit, sugary treats like yogurt drops and honey seed sticks, human foods like bread and cookies, “gourmet” diets, grains, etc), this can lead to significant problems.  When sugars and starches reach the cecum, this allows some very bad bacteria to take over, including Clostridium species and E. coli.  Just like in humans, these bacteria can be very problematic.  They cause the cecum to become very acidic, which is unfriendly for the rest of the microflora living in the cecum.  They also can release toxins that can lead to significant damage to the gut, increase the production of gas, cause diarrhea, and even result in death.  This is especially true in young animals that don’t have a properly established microflora in their cecums.  As such, these kinds of foods should be avoided.

Hopefully we have established that fermentable fibres from hays and grasses are very important, but what about all that indigestible fibre?  Turns out that that is very important too.  Indigestible fibre has a critical role in stimulating gut motility.  Gut motility helps move food and water through the gut to the cecum and colon, and it also helps move indigestible material, like hair, through the gut.  If there isn’t enough indigestible fibre in the diet, the gut motility slows down, increasing the risk gastro-intestinal stasis and even obstruction of the gut.  Indigestible fibre is also important in stimulating appetite, cecotroph ingestion, etc.

How do I find good hay?

Now that we know how important hay is for the teeth and the gastro-intestinal tract, how do we choose what hay to feed to our pet rabbits and our rodents?  The quality of hay is very important – we want very good quality hay to keep our pets healthy.

First off, fresh grass is a wonderful option for our pet small mammals.  It is truly what they evolved eating.  However, that is provided that the grass has not been treated with anything (pesticides, fertilizers, etc), and provided that when your pet is outside eating that fresh grass that they are protected from predators, excessive heat, excessive cold, excessive moisture, and diseases from wild or feral animals (such as parasites, or in some areas of Canada, Rabbit Hemorrhagic Disease Virus).  Being outside eating fresh grass also comes with the added bonus of natural UVB exposure, which is important for the production of vitamin D and the health of bones and teeth, just like in people.  However, in Canada, it is not feasible to allow our pets to graze year round, as we have this unfortunate thing called “winter”.  As such, we have to rely on the dried version of fresh grass (hay) for most of the year.

For our pet species there are two main “categories” of hay that are available to us.  We have “legume” hay, which is alfalfa hay, and we have “grass” hay, like timothy, oat, meadow grass, etc.

Alfalfa hay is high in calcium and protein.  This is an excellent thing for young growing animals and pregnant animals, but not such a great thing for non-breeding adult animals.  In non-breeding adult animals, all of that extra protein is converted to energy, which ultimately can lead to them becoming overweight.  There is also a theory that high calcium foods like alfalfa may increase the risk of bladder sludge and the formation of bladder stones.  As such, we only recommend feeding alfalfa to young growing animals and pregnant animals.

Grass hays, as you can probably guess from the rest of this article, should be the primary part of the diet of our rabbits, guinea pigs, and chinchillas.  The most common and popular grass hay fed to exotic mammals is timothy hay.

When you are choosing hay for your pet, there are a number of factors that you want to evaluate.  Good hay should be dry.  Good hay should be free of dust – dusty hay is often moldy hay, and should never be fed to your pet.  It should be sweet smelling, and should be green.  If it doesn’t look and smell pleasant, I would not recommend feeding that to your pet.

Grass hay should be fed in unlimited amounts every day.  Hay that becomes soiled or trampled should be removed and replaced with fresh hay.  While timothy is the staple hay that most people feed, it can be enriching to mix things up and offer other types of hay as well, such as oat hay and meadow grass hay.  Sometimes if you have a pet that is reluctant to eat hay, including some of these “alternative” hays can be the gateway to getting them to eat hay.  Different pets will have different preferences.  Hay can also be incorporated into various enrichment devices, like toys.  We like offering my pets compressed hay cakes (like the Oxbow Harvest Stacks) so that they must work at them and unravel them, giving them something to do during the day.  We prefer to avoid over-head hay bags (like what is used for horses), as these can cause hay to fall into your pet’s eyes as they are pulling hay out of them – this is especially a concern in guinea pigs, as they have very low corneal sensitivity, and tend not to blink when this happens.  These kinds of hay bags may also increase the risk of your pet inhaling tiny bits of hay material, which can increase the risk of respiratory disease.

Behavioral note

We often have owners tell us that their rabbit or rodent doesn’t like hay, because they never eat it all.  In cases like that, we have unfortunate news – they will never, ever eat it all.  That’s normal and natural and part of their ingrained behavior.  In the wild, rabbits and rodents evaluate the food they are eating, and eat the best, choicest bits first.  The reason they do this is so that if a predator comes around the corner and they have to run for their lives, they ate the best, most nutritious bits, maximizing their chances that they ate enough to survive another day.  Even though most of our pets will never have to face these kinds of dangers, the instincts remain.  As such, they evaluate all of the bits of hay we offer them, and based on factors that are not always evident to us humans, decide that they will eat this piece of hay, but not that piece of hay.  This is normal behavior.  This is why it is so important to give more, fresh hay every single day.  Even though there is hay still in the enclosure, they may have decided that that hay is not worth eating, and therefore will never eat it.

What should I do if my pet is not eating hay?

Our advice is to have your pet examined by a veterinarian and discuss this with your veterinarian.  Sometimes the first sign we see of some diseases, like dental disease, is a change in food preference.  As such, your pet’s reluctance to eat hay could be a sign of illness.  If there is no medical reason for your pet not to eat hay, PHEW!  That’s great!  Now we can give you advice on ways to get your pet to eat hay.

In summary – hay is critically important to the health of our rabbits, guinea pigs, and chinchillas, both for their digestive health and their dental health.  Hay should be the biggest part of their diets, and when hay intake is insufficient it can lead to very serious issues.  We hope this has been helpful and interesting.  If you would like more information on exotic animal care and health, please reach out to Harvest Pointe Animal Hospital.

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