Plan for Feedout: Why Is Structural Fiber Important for the Rumen?

Structural fiber is made up of lignin, cellulose, hemicellulose and cutin, and it’s referred to as “structural” because it’s firm and visible, says Peter Robinson, Ph.D. and Extension specialist at the University of California-Davis. Structural fiber is involved in several important processes in the rumen.

Rumination or cud chewing — It is important in stabilizing the rumen environment and driven by dietary structural fiber. Cud chewing breaks open particles that have been eaten, but not significantly broken up, to facilitate bacterial attachment to particle surfaces. In addition, cud chewing stimulates salivation, which buffers the rumen to prevent
its pH from dropping to cause rumen acidosis.

Nutrient provider — Fiber digestion leads to the creation of volatile fatty acids in the rumen which, once absorbed from the rumen, are a major energy source to support milk production.

Digestibility — Because of the physical nature of structural fiber, it takes up space in the rumen. One of two things can happen:

It’s digested in the rumen — broken down into chemical compounds, such as volatile fatty acids, that are absorbed
It passes out of the rumen — broken down into smaller particles that pass on to the abomasum (true stomach)
Fiber that digests very slowly remains in the rumen and occupies space, which is limited in a rumen, so it results in reduced feed intake. Thus, the rate at which fiber is digested in the rumen is very important. For example, if fiber is 100% digested, but it takes 50 hours in the rumen to get there, then intake will be restricted by rumen space. A more valuable structural fiber is one that is only 50% digested but only needs 14 hours in the rumen to get there because this fiber stimulates cud chewing and salivation and is partly digested, but then passes out of the rumen to allow new fiber to enter in as new DM intake.

When fiber digests faster, it still expresses its structural characteristics, but the particles get smaller and pass out of the rumen and the animal can eat feed. Thus, more nutrients are available to the animal from absorption from the rumen.

Want to Make Silage More Digestible?

Fermentation duration — wait 90 to 120 days before pulling back the plastic
Fermentation efficiency — uniformly apply an inoculant to create a more efficient fermentation process
Maturity at harvest — adequate levels of 33-38% DM offer high starch digestibility, and it’s very easy to break up/process the kernels

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Plan for Feedout: Why Is Structural Fiber Important for the Rumen?

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