lecture 12 - effective fiber

How does a high-forage diet compare to a high-concentrate diet?

High forage means more fiber, more acetate, slower fermentation, and higher rumen pH. High concentrate means more starch, more propionate, faster fermentation, and lower rumen pH.

How does forage-to-concentrate ratio affect dietary energy?

More concentrate increases energy density; more forage decreases it

What happens if dietary energy is too low?

Growth and production decrease

What happens if dietary energy is too high?

Animals may become overconditioned

Why do high-producing animals need enough fiber?

To maintain rumen health while meeting high energy requirements

What happens if high-producing animals consume too much fiber?

Intake and production can decrease

What is physically effective fiber?

Fiber’s ability to stimulate chewing and rumination, based on NDF content and particle size

What two factors determine physically effective fiber?

NDF content and particle size

Why is physically effective fiber important?

It stimulates chewing and saliva production, helping buffer rumen pH

How does forage NDF compare with byproduct NDF?

Forage NDF generally has greater physical effectiveness

Why is byproduct fiber often less effective than forage fiber?

It typically has smaller particle sizes and stimulates less chewing

What is the effective NDF value of alfalfa?

Approximately 95%

What is the effective NDF value of corn silage?

Approximately 95%

What is the effective NDF value of oat hulls?

Approximately 80%

What is the effective NDF value of wheat middlings?

Approximately 50%

What is the effective NDF value of soybean hulls?

Approximately 20%

What can happen if a diet contains too little effective fiber?

Reduced chewing and saliva, lower rumen pH, and increased risk of ruminal acidosis

What can happen if forage particles are too small?

Reduced chewing and rumination, increasing the risk of subacute ruminal acidosis

What can happen if forage particles are too long?

Sorting, reduced intake, and slower passage through the rumen

Why is sorting against long particles a problem?

Animals may consume less effective fiber than the amount offered in the diet

What is the purpose of the Penn State Particle Separator?

To evaluate the particle-size distribution of a feed or total mixed ration

What are the screen sizes of the Penn State Particle Separator?

19 mm, 8 mm, and 4 mm, plus a bottom pan

What does the top screen measure?

The proportion of the largest particles

What does the bottom pan collect?

The smallest particles

Why is particle size important when evaluating a ration?

It helps determine whether the ration provides enough effective fiber without excessive long particles or sorting

What is the overall goal when balancing fiber for high-producing animals?

Provide enough digestible energy and effective fiber to support production and rumen health