What is crude fiber and why does it matter for rabbits?

Crude fiber, crude protein, crude fat, moisture, and calcium. You may have noticed these attributes in our Guaranteed Analysis section of each of our hay or feed pellet products. Or you may have seen them printed on the boxes you received. In either case, we’d thought do a mini-deep-dive on crude fiber as it relates to your beautiful furry friend.

But first, we’d like to clear one thing up: is it spelled fiber or fibre?

The answer is: Both, because they mean the same thing. Fibre is considered a British English variation of the American English, fiber. They both mean “a strand of something”. That’s an official definition. So, feel free to spell it crude fiber or crude fibre; whatever suits your fancy, but when you say “fibre” out loud, you should probably use an accent.

For this post, we’ll stick with fiber.

But what IS crude fiber?

In the simplest terms, crude fiber is a measurement of fiber content. Sometimes referred to as Weende cellulose, crude fiber is the insoluble residue of an acid hydrolysis followed by an alkaline one. This residue contains true cellulose and insoluble lignin.  (source)

Hmm. That doesn’t feel very simple, does it?

Let’s try it again, but with this definition from Pelican Equipment:

 “Crude fibre refers to the residue of a feed that is insoluble after successive, boiling with dilute acid and alkali. This method was originally proposed at the weende experiment station. Hence this method on determination of crude fibre is known as Weende s method of determination of crude fibre.”

 And, in case you were wondering, Wikipedia says “Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants”. In our case, Timothy and Alfalfa Hay.

You know what, just to be safe, let’s ask the internet's newest superstar, ChatGPT to help us out:

ChatGPT Example Response to Crude Fiber in Hay Question
Us: Explain to a 10th grader what crude fiber is in hay for rabbits.

ChatGPT: Crude fiber is the indigestible part of hay that is made up of things like cellulose, lignin, and hemicellulose. It helps to keep a rabbit's digestive system healthy by providing bulk and promoting regular bowel movements. It also helps to wear down a rabbit's continuously growing teeth. Overall, crude fiber is an important component of a healthy diet for rabbits.
 
We're not sure why we chose 10th grader as the audience, but that is a pretty good answer regardless. Well done, ChatGPT. Well done.

While crude fiber is less of a focus for horses, it is incredibly important for rabbits.

Why is crude fiber for rabbits so important?

For one very simple reason: GI motility.  Rabbits are not able to process fiber as effectively as other animals partly because of their ability to excrete quickly.  It is because of this poo efficiency that crude fiber is necessary to facilitate that transaction.  Our friends who authored the Merck Veterinary Manual said it quite well:

Rabbits digest fiber poorly because of the selective separation and rapid excretion of large particles in the hindgut. A generous amount of dietary fiber (~15% crude fiber) is needed to promote intestinal motility and minimize intestinal disease. High-fiber intake can be provided by use of ad lib timothy hay (~30%–35% fiber). Fiber may also absorb bacterial toxins and eliminate them via the hard feces. Diets low in fiber promote an increased incidence of intestinal problems, eg, enterotoxemia.”

The additional benefit of crude fiber for rabbits is it helps with their teeth, which never stop growing. See this post for more info on caring for rabbit teeth.

How does Andy analyze crude fiber?

We are fortunate that our lab partner, AgTest Lab, is located just a few miles down or up the road, depending on how you like to use that phrase. We wanted to get their take on this question, so here is what Nick, the chemist over at the lab, had to say:

Here at the lab we analyze Crude Fiber by NIR. It is a directly analyzed value like Crude Protein or ADF and NDF, and not a calculated value such as RFV or TDN. For the wet chem procedures at Dairy One where our calibrations were created, it is an acid/alkali digestion and an ashing. This allows for the digestion to remove proteins and other non-fiber components, leaving behind only fiber components, that can then be incinerated and the weight lost to combustion is equal to the crude fiber in the sample.

There are a lot of acronyms in there.  We won’t get into their full meanings, but here is what they stand for, so you at least know what words they represent.

NIR – Near Infrared 
ADF - Acid Detergent Fiber
NDF - Neutral Detergent Fiber
RFV – Relative Feed Value
TDN – Total Digestible Nutrient

How much crude fiber should there be in hay for rabbits?

The amount of crude fiber of hay needed for rabbits depends on the overall diet of your funny bunny. (We assume they make you laugh).  Please consult your bun’s dietician for specifics.

Generally speaking, crude fiber in hay for rabbits should be in the mid 20% to mid 30% range. If crude fiber is too low, then there is almost no benefit (from a GI motility need) to your bun; if crude fiber is too high, then the nutrients from digestible fiber decreases.

We also know that percentage of crude fiber will vary by type and season, which is why a range is better than a fixed number.

How much crude fiber is in Andy's Timothy Hay, Alfalfa Hay and feed pellets?

Great question. You might have noticed a lower-than-normal percentage of crude fiber on some of the printed boxes you received. This is a typographical error. A special thanks to one of our first and most informed customers for bringing this to our attention. Because they did, we have re-verified the information with our hay analysis company, updated the information on those boxes - which will take a little while for those changes to hit the market -, and ensured our website has the most current and accurate analysis information.

Crude Fiber in Timothy Hay 1st  Cutting = 34% (max)
Crude Fiber in Timothy Hay 2nd Cutting = 30% (max)
Crude Fiber in Alfalfa Hay = 28% (max)
Crude Fiber in USDA Certified Organic Timothy Hay 1st Cutting = 34% (max)

Call us crazy, but we kinda find the science and biology behind this stuff pretty fascinating. Stay tuned for a breakdown on crude protein and moisture!

Jared is a curious creature seeking to curate creative collections through crafty language without the use of awful alliteration.