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Cayla Iske, PhD
We have all heard that fiber is a very important dietary component for our furry little exotic mammals. But why? And what exactly is fiber anyhow? If you have ever pondered these questions during sleepless nights, you have come to the right place.
What is Fiber?
Fiber is commonly defined as indigestible dietary material. Because it is “indigestible,” it’s easy to assume it’s not important. Don’t we want our animals to be able to digest their food? On the contrary, fiber is hugely important; it’s just digested differently than most macronutrients.
How is Fiber Digested?
When protein, fat, or simple carbohydrates are consumed, they are broken down by digestive enzymes that the body produces and mostly absorbed in the small intestine. Fiber, on the other hand, cannot be broken down by these enzymes and passes through the small intestine relatively unchanged and into the large intestine or caecum. Within these sections of the distal gastrointestinal (GI) tract lives part of the microbiome. This massive biodiversity of organisms (predominately bacteria) flourish and “digest” fiber through a process called fermentation.
The Facts about Fermentation
During fermentation, the enzymes produced by microbes break down fiber into simpler substances (short-chain fatty acids also known as volatile fatty acids) which are then used to fuel the microbes and maintain a healthy population. Some of those short-chain fatty acids are absorbed directly across the intestinal wall and provide the animal itself with energy. So, while fiber isn’t digestible in the typical sense, most herbivores and omnivores can yield energy from fiber.
Not All Fiber is Created Equal
Fiber can be classified in many ways, one of the more common being soluble versus insoluble. Soluble fibers such as pectin, oats, and barley dissolve in water to form a gel and are more fermentable. This slows movement through the digestive tract and makes you feel fuller longer which can lead to reducing food intake. Insoluble fiber, on the other hand, moves through the digestive tract, promotes GI motility, and adds bulk to stools. Hay and bran are examples of insoluble fibers.
Fiber for Our Herbivorous Friends
Rabbits, guinea pigs, and chinchillas are made to utilize fiber. They need large amounts of fiber, particularly insoluble fiber, to stimulate proper GI tract movement (peristalsis) which supports proper function and a healthy environment for the microbiome. As dietary levels of fiber decrease, these species are at higher risks for obesity as low fiber diets often also contain elevated levels of more digestible carbohydrates (easy energy). These extra calories can lead to weight gain which can lead to many secondary issues.
The other issue common with a diet lacking enough fiber is the increased potential for the animal to develop GI stasis or ileus (lack of proper movement of the GI tract). Very commonly, GI stasis is a multifactorial syndrome, but the single biggest potential contributor is lack of adequate fiber intake to stimulate proper peristalsis. Without this constant GI movement, the gut pH can change which leads to shifts in microbial populations and potentially increased gas production all of which contribute to a to a reduced appetite. The reduced feed intake only exacerbates these conditions and can even negatively impact microbe populations in the large intestine and caecum, reducing fermentation capacity.
What About Omnivores?
Fiber is also important for omnivorous species such as rats, mice, hamsters, and gerbils, but isn’t needed in as high of quantities. Fiber quality is also different in these diets, as more soluble fiber may be of particular benefit. Most omnivores do have fermentation capacity, so they can and do derive energy from insoluble fiber, but soluble fiber also hugely benefits these species by helping control feed intake and obesity as well as reducing spikes in glucose after eating which can help reduce insulin related issues (e.g. hyperglycemia, diabetes). Additionally, the fermentation of soluble fibers can help maintain a healthy microbiome and healthy colon.
The Micro-What?
By now, you’ve seen multiple references to the microbiome. So, what is it? The microbiome refers most basically to billions and billions of microscopic living things (e.g. bacteria, protozoa, fungi, etc.) which largely reside in the cecum. As mentioned, these microbes are responsible for fiber digestion but also have a myriad of other functions which are still being explored. Most recently, the microbiome has been found to contribute to immune system and central nervous control and much research is still needed to fully understand the breadth and depth of microbiome functions. This is particularly true for our exotic companion mammals such as rabbits and guinea pigs as we don’t fully understand “normal” microbial populations. This is sure to be an interesting topic in future research and highlights another role of dietary fiber.
