Roughages and Their Essential Role in Rumen Function

black cows on pasture

One of the hardest ideas to get across to people about ruminant nutrition is that ruminants need roughage in their diet to aid the rumen function.  People understand better the need for protein, energy, minerals as such in the diet, but they think that an ingredient containing coarse fiber is useless.  However, a minimum level of roughage is necessary to keep the rumen functioning as it should.

A ruminant’s key niche in the ecosystem is the ability to degrade the complex structural fibers in plants, and metabolize them to make meat and milk that can be consumed by humans, or other animals in the food chain.  Of course, they produce better with plants that have lower fiber levels and are more digestible.

But the fact remains that the rumen works best when the animals have some “long, coarse fiber” in their diet because it stimulates the “roughage effect”.  The roughage effect occurs when this coarse material rubs against the walls of the rumen.  This rubbing action stimulates the muscles in the wall of the rumen to contract and expand, which kind of stirs up the material in the rumen.

This agitation in the rumen helps the slurry inside to mix and become more available for action by the microorganisms.  The more contact the microorganisms make with the slurry in the rumen, the more completely they can break it down.

Another benefit of roughage in a ruminant’s diet is that the coarse materials have to be regurgitated and chewed before it can be metabolized by the microorganisms.  You have probably observed this as an animal “chewing its cud”.

As this material is chewed, saliva is mixed in with it for a better consistency.  A ruminant’s saliva contains buffers that help to keep the acidity down in the rumen.  The fiber digesting microorganisms in the rumen work best in a neutral to slightly acid environment.  Sugars, starches, and other more rapidly metabolized particles in the feed tend to make the rumen more acidic.  So the extended chewing of the fibrous material helps to keep the acidity in the rumen in a range that benefits the fiber digesting microbes.

So you can begin go see why roughage is so important to a ruminant.  But what constitutes roughage?  And how much roughage does a ruminant need?

A general definition of roughage is a feed ingredient that has a high concentration of slowly degradable fiber.  The list of feeds that this definition includes as far as feed tags are concerned includes cottonseed hulls, oat hulls, and soybean hulls.  Another feed tag term that includes high fiber ingredients is “forage products”.  Forage products include any type of hay, silage, or fresh forage that is fed.

However, for a ruminant animal, the term “roughage” is any feed ingredient that has “long roughage”.  By long roughage I mean that the particles are at from 3/8 inch to 1 1/2 inch long or longer.  The importance of the length is that the longer fibrous material will have to be re-chewed by the animal and will remain in the rumen for a greater time period than shorter material.

In fact, when roughage material is ground up into small particles, as some do when mixing or pelleting feeds, it loses some if its roughage effect.  So when choosing what to include as roughage, ground and pelleted items, such as dehydrated alfalfa pellets, should not be counted as roughage.  They contribute fiber to the diet, but not roughage.

Just how much roughage does a ruminant need?  That will vary for each species of ruminant that you deal with.  Cattle, with their large volume rumen and slow passage rate, need more roughage than a deer, with a smaller volume rumen and faster passage rate.  The best way we have of measuring roughage is with the Acid Detergent Fiber (ADF) or Neutral Detergent Fiber (NDF) values we get from forage laboratory analyses.

The acid detergent fiber analysis measures the cellulose and lignin content of a feed.  Cellulose is a digestible form of fiber, while lignin is an indigestible form.  While ADF is a good measure for calculating the energy value of forages, NDF is superior in valuing a feed’s roughage effect because it measures the cellulose, hemi-cellulose (a poorly digestible material), and lignin content of the feed.

Minimal NDF values have been studied on cattle, especially dairy cows, very extensively.  With feeds that have plenty of long roughage, the minimum recommended NDF level is 25%.  Below this, the rumen environment becomes very volatile and potentially dangerous to the animal’s health.

For sheep, goats, and deer, I can only speculate the minimum NDF.  However, with their faster passage rates, and native forage diets that are normally much higher than cattle, I suspect that they could tolerate somewhere around 20% NDF as a minimum level.  However, it is probably safer for the rumen function if their NDF level is around 30%.

Remember, there is a difference between a ruminant selecting a diet that is 25% NDF and you feeding them one that is of the same value.  When animals in a native pasture select forages each day, they have the ability to manipulate their diet.  If they eat something that tends to make their rumen more acidic, they can then search for another forage higher in fiber content to balance out the diet.  And most of what they eat will be of the long roughage category.

In a feedlot, or penned, situation, the difference is that the animals’ selection is limited, if any.  And most of the prepared feeds are ground to some extent to either increase digestibility, or to prevent the stock from picking out just what they like in the ration.

So, when feeding your ruminants in the pen, be aware of the fiber levels.  Unfortunately, the only fiber value printed on feed tags is a Crude Fiber level that doesn’t represent the either ADF or the NDF.  However, you can use it to determine if the feed has enough fiber in it.

The higher the crude fiber value, the more roughage should be in the ration.  Animals on feedlot type of rations, and that are not fed hay along with the feed, should have a feed that contains at least 16% crude fiber for cattle, and 14% crude fiber for smaller ruminants.  However, be sure this fiber is coming from roughage sources such as cottonseed hulls.

In Texas, the percent of the roughage products must be listed on the label in the “Ingredient” section.  Check to see how much roughage is in the feed.  If the roughage level is low and the crude fiber level is high, then the fiber is from a source that probably won’t be giving the animal much of a roughage effect.  Be wary of feeds like that.  You could have some digestive problems arise.

Always be aware that the fiber content of your livestock’s diets.  When moving them from pasture to a penned feeding situation, be sure you introduce grain based feeds gradually, giving the rumen time to adapt to the changing environment.

Roughage is a critical part of a ruminant’s diet and function.  Be aware of what they are eating and you can anticipate, and prevent, digestive problems that can reduce the productivity of your animals.

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